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Yoshinori Dobashi
Faculty of Information Science and Technology　Media and Network Technologies　Information Media Science and Technology
Professor
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Last Updated :2024/05/09

Researcher Profile and Settings

Affiliation

  • Faculty of Information Science and Technology　Media and Network Technologies　Information Media Science and Technology

Job Title

  • Professor

Degree

  • Ph.D(Engineering)（1997/03 Hiroshima University）

URL

J-Global ID

Research Interests

  • Computer Graphics   Visual Simulation   Sound Simulation   Photorealistic Rendering   Fluid Simulation   Lighting Simulation   Real-time Rendering   Efficient Rendering   Atmospheric Scattering   Light Scattering   User Interfaces   

Research Areas

  • Informatics / High-performance computing / computer graphics

Educational Organization

Academic & Professional Experience

  • 2020/10 - Today 北海道大学大学院情報科学研究院
  • 2008 - 2020/09 北海道大学 大学院・情報科学研究科 大学院・情報科学研究科 准教授

Research Activities

Published Papers

  • Yoshinori Dobashi, Naoto Ishikawa, Kei Iwasaki
    ACM Transactions on Graphics 42 (6) 1 - 11 0730-0301 2023/12/05 
    Artificial light sources make our daily life convenient, but cause a severe problem called light pollution. We propose a novel system for efficient visualization of light pollution in the night sky. Numerous methods have been proposed for rendering the sky, but most of these focus on rendering of the daytime or the sunset sky where the sun is the only, or dominant light source. For the visualization of the light pollution, however, we must consider many city light sources on the ground, resulting in excessive computational cost. We address this problem by precomputing a set of intensity distributions for the sky illuminated by city light at various locations and with different atmospheric conditions. We apply a principal component analysis and fast Fourier transform to the precomputed distributions, allowing us to efficiently visualize the extent of the light pollution. Using this method, we can achieve one to two orders of magnitudes faster computation compared to a naive approach that simply accumulates the scattered intensity for each viewing ray. Furthermore, the fast computation allows us to interactively solve the inverse problem that determines the city light intensity needed to reduce light pollution. Our system provides the user with both a forward and inverse investigation tool for the study and minimization of light pollution.
  • Shogo Umeyama, Yoshinori Dobashi
    IEICE Transactions on Information & Systems 106 (2) 267 - 270 2023/02
  • Masataka Sawayama, Yoshinori Dobashi, Makoto Okabe, Kenchi Hosokawa, Takuya Koumura, Toni P Saarela, Maria Olkkonen, Shin'ya Nishida
    Journal of vision 22 (2) 17 - 17 2022/02/01 
    Complex visual processing involved in perceiving the object materials can be better elucidated by taking a variety of research approaches. Sharing stimulus and response data is an effective strategy to make the results of different studies directly comparable and can assist researchers with different backgrounds to jump into the field. Here, we constructed a database containing several sets of material images annotated with visual discrimination performance. We created the material images using physically based computer graphics techniques and conducted psychophysical experiments with them in both laboratory and crowdsourcing settings. The observer's task was to discriminate materials on one of six dimensions (gloss contrast, gloss distinctness of image, translucent vs. opaque, metal vs. plastic, metal vs. glass, and glossy vs. painted). The illumination consistency and object geometry were also varied. We used a nonverbal procedure (an oddity task) applicable for diverse use cases, such as cross-cultural, cross-species, clinical, or developmental studies. Results showed that the material discrimination depended on the illuminations and geometries and that the ability to discriminate the spatial consistency of specular highlights in glossiness perception showed larger individual differences than in other tasks. In addition, analysis of visual features showed that the parameters of higher order color texture statistics can partially, but not completely, explain task performance. The results obtained through crowdsourcing were highly correlated with those obtained in the laboratory, suggesting that our database can be used even when the experimental conditions are not strictly controlled in the laboratory. Several projects using our dataset are underway.
  • Ryoma Hashimoto, Yoshinori Dobashi
    SIGGRAPH Asia 2022 Posters 18 - 2 2022
  • Shogo Umeyama, Yoshinori Dobashi
    The 30th Pacific Conference on Computer Graphics and Applications, PG 2022, Short Papers, Posters, and Work-in-Progress Papers 15 - 16 2022
  • Kento Mannen, Yoshinori Dobashi
    SN Computer Science 3 (1) 86 - 86 2022
  • Shintaro Fuji, Syuhei Sato, Kei Iwasaki, Yoshinori Dobashi, Shangce Gao, Zheng Tang
    SIGGRAPH Posters 42 - 2 2022
  • Hyuga Saito, Syuhei Sato, Yoshinori Dobashi
    SIGGRAPH Asia 2021 Posters 31 - 2 2021
  • 大場誉幸, 土橋宜典
    映像情報メディア学会誌(Web) 75 (3) 1881-6908 2021 [Refereed]
  • Yuto Matsunaga, Naofumi Aoki, Yoshinori Dobashi, Tetsuya Kojima
    International Conference on Artificial Intelligence in Information and Communication(ICAIIC) 31 - 35 2021 [Refereed]
  • Syuhei Sato, Yoshinori Dobashi, Theodore Kim
    ACM Trans. Graph. 40 (4) 161 - 7 2021 [Refereed]
  • Namo Podee, Nelson Max, Kei Iwasaki, Yoshinori Dobashi
    Comput. Vis. Media 7 (2) 201 - 215 2021 [Refereed]
  • Resampling-aware Weighting Functions for Bidirectional Path Tracing Using Multiple Light Sub-Paths
    Kosuke Nabata, Kei Iwasaki, Yoshinori Dobashi
    ACM Transactions on Graphics 39 (2) 15:1 - 15:11 2020/03 [Refereed][Not invited]
  • Naoto Ishikawa, Yoshinori Dobashi
    Comput. Vis. Media 6 (4) 445 - 454 2020 [Refereed]
  • Kosuke Nabata, Kei Iwasaki, Yoshinori Dobashi
    Comput. Graph. Forum 39 (7) 219 - 230 2020 [Refereed]
  • Makoto Okabe, Keita Noda, Yoshinori Dobashi, Ken Anjyo
    IEEE Computer Graphics and Applications 40 (1) 127 - 139 2020 [Refereed]
  • Namo Podee, Nelson Max, Kei Iwasaki, Yoshinori Dobashi
    Special Interest Group on Computer Graphics and Interactive Techniques Conference, SIGGRAPH 2019, Posters, Los Angeles, California, USA, July 28 - August 1, 2019. ACM 50:1-50:2  2019 [Refereed][Not invited]
  • Atsuhito Udo, Naofumi Aoki, Yoshinori Dobashi, Tsuyoshi Yamamoto
    International Conference on Artificial Intelligence in Information and Communication, ICAIIC 2019, Okinawa, Japan, February 11-13, 2019 IEEE 128 - 131 2019 [Refereed][Not invited]
  • Masayuki Tamiya, Yoshinori Dobashi
    2019 International Conference on Cyberworlds, CW 2019, Kyoto, Japan, October 2-4, 2019 IEEE 395 - 398 2019 [Refereed][Not invited]
  • Naho Sakao, Yoshinori Dobashi
    2019 International Conference on Cyberworlds, CW 2019, Kyoto, Japan, October 2-4, 2019 IEEE 391 - 394 2019 [Refereed][Not invited]
  • Yu Murata, Yoshinori Dobashi
    2019 International Conference on Cyberworlds, CW 2019, Kyoto, Japan, October 2-4, 2019 IEEE 374 - 377 2019 [Refereed][Not invited]
  • Hideki Todo, Array, Masataka Sawayama, Yoshinori Dobashi, Masanori Kakimoto
    The Visual Computer 35 (6-8) 811 - 822 2019 [Refereed][Not invited]
  • Yuto Matsunaga, Tetsuya Kojima, Naofumi Aoki, Yoshinori Dobashi, Tsuyoshi Yamamoto
    IEICE Transactions 102-D (6) 1119 - 1125 2019 [Refereed][Not invited]
  • Takashi Ijiri, Hideki Todo, Akira Hirabayashi, Kenji Kohiyama, Yoshinori Dobashi
    PLoS ONE 13 (4) 1932-6203 2018/04/01 [Refereed][Not invited]
     
    In this paper, we present a three-dimensional (3D) digitization technique for natural objects, such as insects and plants. The key idea is to combine X-ray computed tomography (CT) and photographs to obtain both complicated 3D shapes and surface textures of target specimens. We measure a specimen by using an X-ray CT device and a digital camera to obtain a CT volumetric image (volume) and multiple photographs. We then reconstruct a 3D model by segmenting the CT volume and generate a texture by projecting the photographs onto the model. To achieve this reconstruction, we introduce a technique for estimating a camera position for each photograph. We also present techniques for merging multiple textures generated from multiple photographs and recovering missing texture areas caused by occlusion. We illustrate the feasibility of our 3D digitization technique by digitizing 3D textured models of insects and flowers. The combination of X-ray CT and a digital camera makes it possible to successfully digitize specimens with complicated 3D structures accurately and allows us to browse both surface colors and internal structures.
  • Makoto Okabe, Yoshinori Dobashi, Ken Anjyo
    Visual Computer 34 (3) 347 - 358 0178-2789 2018/03/01 [Refereed][Not invited]
     
    We present a system to quickly and easily create an animation of water scenes in a single image. Our method relies on a database of videos of water scenes and video retrieval technique. Given an input image, alpha masks specifying regions of interest, and sketches specifying flow directions, our system first retrieves appropriate video candidates from the database and create the candidate animations for each region of interest as the composite of the input image and the retrieved videos: this process spends less than one minute by taking advantage of parallel distributed processing. Our system then allows the user to interactively control the speed of the desired animation and select the appropriate animation. After selecting the animation for all the regions, the resulting animation is completed. Finally, the user optionally applies a texture synthesis algorithm to recover the appearance of the input image. We demonstrate that our system allows the user to create a variety of animations of water scenes.
  • Yuto Matsunaga, Tetsuya Kojima, Naofumi Aoki, Yoshinori Dobashi, Tsuyoshi Yamamoto
    Acoustical Science and Technology 39 (1) 37 - 39 1347-5177 2018 [Refereed][Not invited]
  • Kaisei Sakurai, Yoshinori Dobashi, Kei Iwasaki, Tomoyuki Nishita
    ACM Trans. Graph. 37 (4) 158:1-158:10  0730-0301 2018 [Refereed][Not invited]
     
    A great deal of attention has been devoted to the fabrication of reflectors that can display different color images when viewed from different directions not only in industry but also for the arts. Although such reflectors have previously been successfully fabricated, the number of images displayed has been limited to two or they suffer from ghosting artifacts where mixed images appear. Furthermore, the previous methods need special hardware and/or materials to fabricate the reflectors. Thus, those techniques are not suitable for printing reflectors on everyday personal objects made of different materials, such as name cards, letter sheets, envelopes, and plastic cases. To overcome these limitations, we propose a method for fabricating reflectors using a standard ultraviolet printer (UV printer). UV printer can render a specified 2D color pattern on an arbitrary material and by overprinting the printed pattern can be raised, that is, the printed pattern becomes a microstructure having color and height. We propose using these microstructures to formulate a method for designing spatially varying reflections that can display different target images when viewed from different directions. The microstructure is calculated by minimizing an objective function that measures the differences between the intensities of the light reflected from the reflector and that of the target image. We show several fabricated reflectors to demonstrate the usefulness of the proposed method.
  • Syuhei Sato, Yoshinori Dobashi, Theodore Kim, Tomoyuki Nishita
    ACM Trans. Graph. 37 (4) 84:1-84:9  0730-0301 2018 [Refereed][Not invited]
     
    Generating realistic fluid simulations remains computationally expensive, and animators can expend enormous effort trying to achieve a desired motion. To reduce such costs, several methods have been developed in which high-resolution turbulence is synthesized as a post process. Since global motion can then be obtained using a fast, low-resolution simulation, less effort is needed to create a realistic animation with the desired behavior. While much research has focused on accelerating the low-resolution simulation, the problem controlling the behavior of the turbulent, high-resolution motion has received little attention. In this paper, we show that style transfer methods from image editing can be adapted to transfer the turbulent style of an existing fluid simulation onto a new one. We do this by extending example-based image synthesis methods to handle velocity fields using a combination of patch-based and optimization-based texture synthesis. This approach allows us to take into account the incompressibility condition, which we have found to be a important factor during synthesis. Using our method, a user can easily and intuitively create high-resolution fluid animations that have a desired turbulent motion.
  • Tetsuya Takahashi, Yoshinori Dobashi, Tomoyuki Nishita, Ming C. Lin
    Comput. Graph. Forum 37 (1) 313 - 324 2018 [Refereed][Not invited]
  • Syuhei Sato, Yoshinori Dobashi, Tomoyuki Nishita
    ACM Trans. Graph. 37 (5) 173:1-173:12  0730-0301 2018 [Refereed][Not invited]
     
    The computational cost for creating realistic fluid animations by numerical simulation is generally expensive. In digital production environments, existing precomputed fluid animations are often reused for different scenes in order to reduce the cost of creating scenes containing fluids. However, applying the same animation to different scenes often produces unacceptable results, so the animation needs to be edited. In order to help animators with the editing process, we develop a novel method for synthesizing the desired fluid animations by combining existing flow data. Our system allows the user to place flows at desired positions and combine them. We do this by interpolating velocities at the boundaries between the flows. The interpolation is formulated as a minimization problem of an energy function, which is designed to take into account the inviscid, incompressible Navier-Stokes equations. Our method focuses on smoke simulations defined on a uniform grid. We demonstrate the potential of our method by showing a set of examples, including a large-scale sandstorm created from a few flow data simulated in a small-scale space.
  • Yoshinori Dobashi, Kei Iwasaki, Makoto Okabe, Takashi Ijiri, Hideki Todo
    Visual Computer 35 (2) 1 - 16 0178-2789 2017/12/04 [Refereed][Not invited]
     
    This paper proposes an inverse approach for modeling the appearance of interwoven cloth. Creating the desired appearance in cloth is difficult because many factors, such as the type of thread and the weaving pattern, have to be considered. Design tools that enable the desired visual appearance of the cloth to be replicated are therefore beneficial for many computer graphics applications. In this paper, we focus on the design of the appearance of interwoven cloth whose reflectance properties are significantly affected by the weaving patterns. Although there are several systems that support editing of weaving patterns, they lack an inverse design tool that automatically determines the spatially varying bidirectional reflectance distribution function (BRDF) from the weaving patterns required to make the cloth display the desired appearance. We propose a method for computing the cloth BRDFs that can be used to display the desired image provided by the user. We formulate this problem as a cost minimization and solve it by computing the shortest path of a graph. We demonstrate the effectiveness of the method with several examples.
  • Yuto Matsunaga, Tetsuya Kojima, Naofumi Aoki, Yoshinori Dobashi, Tsuyoshi Yamamoto
    2017 8th International Workshop on Signal Design and Its Applications in Communications, IWSDA 2017 131 - 134 2017/11/03 [Refereed][Not invited]
     
    In this paper, we propose a novel concept of a digital watermark for music data that focuses on the use of sound effect techniques. This paper describes our proposed technique, which utilizes the distortion effect, frequently employed especially for guitar and bass instruments. In addition, this paper describes the experimental results of evaluating the robustness of the proposed technique against some basic attacks including MP3 coding, tempo alteration, and pitch alteration. It is demonstrated that the proposed technique potentially has good performance against such attacks.
  • Takuya Yamakawa, Yoshinori Dobashi, Makoto Okabe, Kei Iwasaki, Tsuyoshi Yamamoto
    Proceedings - SCCG 2017: 33rd Spring Conference on Computer Graphics 2017- 4:1-4:8  2017/05/15 [Refereed][Not invited]
     
    We present a system that automatically suggests the furniture layout when one moves into a new house, taking into account the furniture layout in the previous house. In our method, the input to our system comprises the floor plans of the previous and new houses, and the furniture layout in the previous house. The furniture layout for the whole house is suggested. This method builds on a previous furniture layout method with which the furniture layout for a single room only is computed. In this paper, we propose a new method that can suggest the furniture layout for multiple rooms in the new house. To deal with this problem, we took a heuristic approach in developing a cost function by adding some new cost functions to the previous method. We show various layouts computed using our method, which demonstrates the effectiveness of it.
  • Syuhei Sato, Keisuke Mizutani, Yoshinori Dobashi, Tomoyuki Nishita, Tsuyoshi Yamamoto
    COMPUTER ANIMATION AND VIRTUAL WORLDS 28 (3-4) 1546-4261 2017/05 [Refereed][Not invited]
     
    Visual simulation of fire plays an important role in many applications, such as movies and computer games. In these applications, artists are often requested to synthesize realistic fire with a particular behavior. To meet such requirement, we present a feedback control method for fire simulations. The user can design the shape of fire by placing a set of control points. Our method generates a force field and automatically adjusts a temperature at a fire source, based on user specified control points. Experimental results show that our method can control the fire shape.
  • Syuhei Sato, Yoshinori Dobashi, Tomoyuki Nishita
    IGGRAPH ASIA 2017 TECHNICAL BRIEFS (SA'17) 2017 
    The computational cost of physically-based fluid simulation for generating realistic animations is expensive. Therefore, it takes a long time for an animator to create the desired animation. To reduce such costs, several methods have been developed that employ an approach in which turbulence is synthesized as a post process. Since, with this approach, global motion can be obtained using low-resolution fluid simulation, realistic animations with the desired behavior can be created at low cost. In the field of image editing, style transfer methods, which can efficiently achieve the desired stylization by transferring features of an example image to a user-specified image, have been proposed. We combine these concepts and present a novel style transfer method for turbulence by reusing the existing fluid animations. Our system allows the user to transfer turbulent motion from one flow field to other flow fields. We do this by extending example-based image synthesis methods to the flow field: a patch-based synthesis and an optimization-based texture synthesis. Our method is designed such that the resulting flow fields satisfy the incompressibility condition. Our method can intuitively and easily create high-resolution fluid animations with the desired turbulent motion.
  • Sawayama Masataka, Okabe Makoto, Nishida Shin'ya, Dobashi Yoshinori
    The Japanese Journal of Psychonomic Science 日本基礎心理学会 36 (1) 56 - 65 2017 

    This research note reviews experimental methods to elucidate the visual processing underlying material perception, and considers how to generate experimental stimuli of three-dimensional shapes for the experiments. For generation of a computer graphics image of a three-dimensional object, it has been widely known that its shape features can affect the material appearance of the object. However, it is not established how to systematically control the shape features to investigate the effect. Here we suggest to utilize texture synthesis algorithms. Specifically, we used a height map of a three-dimensional object as a source image, and synthesized a novel height map by using a texture synthesis algorithm. We tested three algorithms to generate the height maps; i) synthesis based on image statistics, ii) example-based synthesis, and iii) synthesis using a convolutional neural network. We discuss how effective the texture synthesis algorithms are to investigate the effect of the shape features on the material perception.

  • Kei Iwasaki, Yoshinori Dobashi, Makoto Okabe
    Proceedings of the Computer Graphics International Conference, CGI 2017, Yokohama, Japan, June 27 - 30, 2017 ACM 28:1-28:6  2017 [Refereed][Not invited]
  • Yoshinori Dobashi, Kei Iwasaki, Yonghao Yue, Tomoyuki Nishita
    Visual Informatics 1 (1) 1 - 8 2017 [Refereed][Not invited]
  • Syuhei Sato, Yoshinori Dobashi, Tomoyuki Nishita
    SA 2016 - SIGGRAPH ASIA 2016 Technical Briefs 4:1 - 4:4 2016/11/28 [Refereed][Not invited]
     
    The computational cost for creating realistic fluid animations by simulation is generally very expensive. In digital production environment, existing precomputed fluid animations are often reused for different scenes in order to reduce the cost for creating scenes containing fluids. However, applying same animations to different scenes produces unacceptable results, so the animation needs to be edited. In order to do this, we develop a method for synthesizing desired flow fields by combining existing flow fields. Our system allows the user to place existing flow fields at arbitrary positions, and combine them by interpolating the regions between these flow fields, to synthesize a new flow field. The interpolation of the flow fields is realized by solving a minimization problem. Our minimization problem consists of two energy functions for smoothly interpolating the velocities and satisfying the incompressibility. Our method can create the desired incompressible flow fields by reusing existing flow fields.
  • K. Nabata, K. Iwasaki, Y. Dobashi, T. Nishita
    COMPUTER GRAPHICS FORUM 35 (7) 431 - 439 0167-7055 2016/10 [Refereed][Not invited]
     
    The popularity of many-light rendering, which converts complex global illumination computations into a simple sum of the illumination from virtual point lights (VPLs), for predictive rendering has increased in recent years. A huge number of VPLs are usually required for predictive rendering at the cost of extensive computational time. While previous methods can achieve significant speedup by clustering VPLs, none of these previous methods can estimate the total errors due to clustering. This drawback imposes on users tedious trial and error processes to obtain rendered images with reliable accuracy. In this paper, we propose an error estimation framework for many-light rendering. Our method transforms VPL clustering into stratified sampling combined with confidence intervals, which enables the user to estimate the error due to clustering without the costly computing required to sum the illumination from all the VPLs. Our estimation framework is capable of handling arbitrary BRDFs and is accelerated by using visibility caching, both of which make our method more practical. The experimental results demonstrate that our method can estimate the error much more accurately than the previous clustering method.
  • Mikio Shinya, Yoshinori Dobashi, Michio Shiraishi, Motonobu Kawashima, Tomoyuki Nishita
    COMPUTER GRAPHICS FORUM 35 (7) 373 - 382 0167-7055 2016/10 [Refereed][Not invited]
     
    Fast realistic rendering of objects in scattering media is still a challenging topic in computer graphics. In presence of participating media, a light beam is repeatedly scattered by media particles, changing direction and getting spread out. Explicitly evaluating this beam distribution would enable efficient simulation of multiple scattering events without involving costly stochastic methods. Narrow beam theory provides explicit equations that approximate light propagation in a narrow incident beam. Based on this theory, we propose a closed-form distribution function for scattered beams. We successfully apply it to the image synthesis of scenes in which scattering occurs, and show that our proposed estimation method is more accurate than those based on the Wentzel-Kramers-Brillouin (WKB) theory.
  • Yongsheng Zhang, Tsuyoshi Yamamoto, Yoshinori Dobashi
    NEUROCOMPUTING 207 684 - 692 0925-2312 2016/09 [Refereed][Not invited]
     
    Object retrieval has attracted much research attention in recent years. Confronting object retrieval, how to estimate the relevance among objects is a challenging task. In this paper, we focus on view-based object retrieval and propose a multi-scale object retrieval algorithm via learning on graph from multi modal data. In our work, shape features are extracted from each view of objects. The relevance among objects is formulated in a hypergraph Structure, where the distance of different views in. the feature space is employed to generate the connection in the hypergraph. To achieve better representation performance, we propose a multi-scale hypergraph structure to model object correlations. The learning on graph is conducted to estimate the optimal relevance among these objects, which are used for object retrieval. To evaluate the performance of the proposed method, we conduct experiments on the National Taiwan University dataset and the ETH dataset. Experimental results and comparisons with the state-of-the-art methods demonstrate the effectiveness of the proposed method. (C) 2016 Elsevier B.V. All rights reserved.
  • Syuhei Sato, Yoshinori Dobashi, Tomoyuki Nishita
    SIGGRAPH 2016 - ACM SIGGRAPH 2016 Posters 62:1-62:2  2016/07/24 [Refereed][Not invited]
     
    In this paper, we develop a method for synthesizing desired flow fields by combining existing multiple flow fields. Our system al-lows the user to specify arbitrary regions of the precomputed flow fields and combine them to synthesize a new flow field. In order to maintain plausible physical behavior, we ensure the incompressibility for the combined flow field. To address this, we use stream functions for representing the flow fields. However, there exist discontinuities at the boundaries between the combined flow fields, resulting in unnatural animation of fluids. In order to remove the discontinuities, we apply Poisson image editing to the stream functions.
  • Yoshinori Dobashi, Takashi Ijiri, Hideki Todo, Kei Iwasaki, Makoto Okabe, Satoshi Nishimura
    SIGGRAPH 2016 - ACM SIGGRAPH 2016 Posters 28:1  2016/07/24 [Refereed][Not invited]
     
    Realistic image synthesis is an important research goal in computer graphics. One important factor to achieve this goal is a bidirectional reflectance distribution function (BRDF) that mainly governs an appearance of an object. Many BRDF models have therefore been developed. A physically-based BRDF based on microfacet theory [Cook and Torrance 1982] is widely used in many applications since it can produce highly realistic images. The microfacetbased BRDF consists of three terms a Fresnel, a normal distribution, and a geometric functions. There are many analytical and approximate models for each of these terms.
  • Syuhei Sato, Yoshinori Dobashi, Tomoyuki Nishita
    ACM SIGGRAPH 2016 posters 62:1 - 62:1 2016/07 [Refereed][Not invited]
  • Takuya Yamakawa, Yoshinori Dobashi, Tsuyoshi Yamamoto
    ACM International Conference Proceeding Series 23-25- 173 - 179 2016/05/23 [Refereed][Not invited]
     
    Furniture layout design is a challenging problem,and several methods have recently been proposed. Although the lighting environment in a room has a strong relationship with the fur-niture functionality, the previous methods completely over-looked it in designing furniture layout. This paper addresses this problem we propose an efficient method for computing furniture layout taking into account the lighting environ-ment. We propose a new cost function that evaluates the lighting environment taking into account inter-reections of light. A fast method for evaluating the cost function is also proposed. We demonstrate that our method improves the quality and usability of furniture layout by taking into ac-count the lighting environment.
  • Keisuke Mizutani, Yoshinori Dobashi, Tsuyoshi Yamamoto
    Proceedings of the 11th Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications (VISIGRAPP 2016) - Volume 1: GRAPP, Rome, Italy, February 27-29, 2016. SciTePress 242 - 247 2016 [Refereed][Not invited]
  • Masanori Sotozaki, Yoshinori Dobashi, Tsuyoshi Yamamoto
    Proceedings of the 11th Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications (VISIGRAPP 2016) - Volume 1: GRAPP, Rome, Italy, February 27-29, 2016. SciTePress 236 - 241 2016 [Refereed][Not invited]
  • Tetsuya Takahashi, Yoshinori Dobashi, Issei Fujishiro, Tomoyuki Nishita
    VISUAL COMPUTER 32 (1) 57 - 66 0178-2789 2016/01 [Refereed][Not invited]
     
    We propose a particle-based hybrid method for simulating volume preserving viscoelastic fluids with large deformations. Our method combines smoothed particle hydrodynamics (SPH) and position-based dynamics (PBD) to approximate the dynamics of viscoelastic fluids. While preserving their volumes using SPH, we exploit an idea of PBD and correct particle velocities for viscoelastic effects not to negatively affect volume preservation of materials. To correct particle velocities and simulate viscoelastic fluids, we use connections between particles which are adaptively generated and deleted based on the positional relations of the particles. Additionally, we weaken the effect of velocity corrections to address plastic deformations of materials. For one-way and two-way fluid-solid coupling, we incorporate solid boundary particles into our algorithm. Several examples demonstrate that our hybrid method can sufficiently preserve fluid volumes and robustly and plausibly generate a variety of viscoelastic behaviors, such as splitting and merging, large deformations, and Barus effect.
  • Tatsuki Kawaguchi, Yoshinori Dobashi, Tsuyoshi Yamamoto
    IEICE TRANSACTIONS ON INFORMATION AND SYSTEMS E98D (11) 2034 - 2037 1745-1361 2015/11 [Refereed][Not invited]
     
    Controlling fluid simulation is one of the important research topics in computer graphics. In this paper, we focus on controlling the simulation of cumuliform cloud formation. Using a previously proposed method for controlling cloud simulation the convergence speed is very slow; therefore, it takes a long time before the clouds form the desired shapes. We improved the method and accelerated the convergence by introducing a new mechanism for controlling the amount of water vapor added. We demonstrate the effectiveness of the proposed method by several examples.
  • Makoto Okabe, Yoshinori Dobashi, Ken Anjyo, Rikio Onai
    ACM TRANSACTIONS ON GRAPHICS 34 (4) 93  0730-0301 2015/08 [Refereed][Not invited]
     
    We propose a method of three-dimensional (3D) modeling of volumetric fluid phenomena from sparse multi-view images (e.g., only a single-view input or a pair of front- and side-view inputs). The volume determined from such sparse inputs using previous methods appears blurry and unnatural with novel views; however, our method preserves the appearance of novel viewing angles by transferring the appearance information from input images to novel viewing angles. For appearance information, we use histograms of image intensities and steerable coefficients. We formulate the volume modeling as an energy minimization problem with statistical hard constraints, which is solved using an expectation maximization (EM)-like iterative algorithm. Our algorithm begins with a rough estimate of the initial volume modeled from the input images, followed by an iterative process whereby we first render the images of the current volume with novel viewing angles. Then, we modify the rendered images by transferring the appearance information from the input images, and we thereafter model the improved volume based on the modified images. We iterate these operations until the volume converges. We demonstrate our method successfully provides natural-looking volume sequences of fluids (i.e., fire, smoke, explosions, and a water splash) from sparse multiview videos. To create production-ready fluid animations, we further propose a method of rendering and editing fluids using a commercially available fluid simulator.
  • Syuhei Sato, Yoshinori Dobashi, Yonghao Yue, Kei Iwasaki, Tomoyuki Nishita
    VISUAL COMPUTER 31 (6-8) 959 - 965 0178-2789 2015/06 [Refereed][Not invited]
     
    Physically based fluid simulations usually require expensive computation cost for creating realistic animations. We present a technique that allows the user to create various fluid animations from an input fluid animation sequence, without the need for repeatedly performing simulations. Our system allows the user to deform the flow field in order to edit the overall fluid behavior. In order to maintain plausible physical behavior, we ensure the incompressibility to guarantee the mass conservation. We use a vector potential for representing the flowfields to realize such incompressibility-preserving deformations. Our method first computes (time-varying) vector potentials from the input velocity field sequence. Then, the user deforms the vector potential, and the system computes the deformed velocity field by taking the curl operator on the vector potential. The incompressibility is thus obtained by construction. We show various examples to demonstrate the usefulness of our method.
  • Tetsuya Takahashi, Yoshinori Dobashi, Issei Fujishiro, Tomoyuki Nishita, Ming C. Lin
    COMPUTER GRAPHICS FORUM 34 (2) 493 - 502 0167-7055 2015/05 [Refereed][Not invited]
     
    We propose a stable and efficient particle-based method for simulating highly viscous fluids that can generate coiling and buckling phenomena and handle variable viscosity. In contrast to previous methods that use explicit integration, our method uses an implicit formulation to improve the robustness of viscosity integration, therefore enabling use of larger time steps and higher viscosities. We use Smoothed Particle Hydrodynamics to solve the full form of viscosity, constructing a sparse linear system with a symmetric positive definite matrix, while exploiting the variational principle that automatically enforces the boundary condition on free surfaces. We also propose a new method for extracting coefficients of the matrix contributed by second-ring neighbor particles to efficiently solve the linear system using a conjugate gradient solver. Several examples demonstrate the robustness and efficiency of our implicit formulation over previous methods and illustrate the versatility of our method.
  • Charles Welton Ferreira Barbosa, Yoshinori Dobashi, Tsuyoshi Yamamoto
    COMPUTER ANIMATION AND VIRTUAL WORLDS 26 (3-4) 367 - 375 1546-4261 2015/05 [Refereed][Not invited]
     
    In this paper, we propose a method for the simulation of clouds using particles exclusively. The method is based on position based fluids, which simulates fluids using position constraints. To reduce the simulation time, we have used adaptive splitting and merging to concentrate computation on regions where it is most needed. When clouds are formed, particles are split so as to add more details to the generated cloud surface and when they disappear, particles are merged back. We implement our adaptive method on the Graphics Processing Unit (GPU) to accelerate the computation. While the splitting portion is easily parallelizable, the merge portion is not. We develop a simple algorithm to address this problem and achieve reasonable simulation times. Copyright (c) 2015John Wiley & Sons, Ltd.
  • Xiaoxiong Xing, Yoshinori Dobashi, Tsuyoshi Yamamoto, Yosuke Katsura, Ken Anjyo
    IEICE TRANSACTIONS ON INFORMATION AND SYSTEMS E98D (2) 404 - 411 1745-1361 2015/02 [Refereed][Not invited]
     
    We present an algorithm for efficient rendering of animated hair under a dynamic, low-frequency lighting environment. We use spherical harmonics (SH) to represent the environmental light. The transmittances between a point on a hair strand and the light sources are also represented by SH functions. Then, a convolution of SH functions and the scattering function of a hair strand is precomputed. This allows us to efficiently compute the intensity at a point on the hair. However, the computation of the transmittance is very time-consuming. We address this problem by using a voxel-based approach: the transmittance is computed by using a voxelized hair model. We further accelerate the computation by sampling the voxels. By using our method, we can render a hair model consisting of tens of thousands of hair strands at interactive frame rates.
  • Munehiro Doi, Yoshinori Dobashi, Hideaki Tamori, Tsuyoshi Yamamoto
    SIXTH INTERNATIONAL CONFERENCE ON GRAPHIC AND IMAGE PROCESSING (ICGIP 2014) 9443 0277-786X 2015 [Refereed][Not invited]
     
    We propose a novel method for the automatic generation of the spatial image filter sequences based on Genetic Programming (GP). In this method, the filter sequences consist of the filters which process Image-Value Pairs. This idea allows the filter sequences to contain not only image processing, but also numerical operations. And we exploit the popular method of the multi-objective optimization to generate the robust filter sequences. We demonstrate the generation of the background elimination filter from the pictures of flowers and also demonstrate the generation of the image classification filters.
  • Kei Suzuki, Yoshinori Dobashi, Tsuyoshi Yamamoto
    14TH ACM SIGGRAPH INTERNATIONAL CONFERENCE ON VIRTUAL REALITY CONTINUUM AND ITS APPLICATIONS IN INDUSTRY, VRCAI 2015 51 - 54 2015 [Refereed][Not invited]
     
    For creating synthetic images of outdoor scenes, clouds play an important role to enhance the realism of the scene. Therefore, many methods have been proposed for visual simulation of clouds. However, in order to generate realistic clouds, the user has to adjust many parameters involved in the methods. Although choosing appropriate parameters is not a difficult task for experienced users, it becomes a serious problem for novice users who have no sufficient prior knowledge on nether the parameters nor the methods. In order to address this problem, we propose a sketch-based retrieval system for cloud volumes by using a precomputed database. The database of cloud volumes is generated in advance by numerical analysis of atmospheric fluid dynamics. Next, the user sketches the desired shape of clouds at the desired position on the screen and then our system searches for the optimal cloud volume from the database. Our system allows the novice users to intuitively design the desired and realistic cloud scene.
  • Yoshinori Dobashi, Yuhei Shibukawa, Munehiro Tada, Syuhei Sato, Kei Iwasaki, Tsuyoshi Yamamoto
    Eurographics 2015 - Short Papers, Zurich, Switzerland, May 4th - 8th, 2015. Eurographics Association 49 - 52 2015 [Refereed][Not invited]
  • Syuhei Sato, Yoshinori Dobashi, Kei Iwasaki, Tsuyoshi Yamamoto, Tomoyuki Nishita
    SIGGRAPH Asia 2014 Technical Briefs, SA 2014 4:1-4:4  2014/11/24 [Refereed][Not invited]
     
    Recently, visual simulation of fluids has become an important element in many applications, such as movies and computer games. These fluid animations are usually created by physically-based fluid simulation. However, the simulation often requires very expensive computational cost for creating realistic fluid animations. Therefore, when the user tries to create various fluid animations, he or she must execute fluid simulation repeatedly, which requires a prohibitive computational time. To address this problem, this paper proposes a method for deforming velocity fields of fluids while preserving the divergence-free condition. In this paper, we focus on grid-based 2D fluid simulations. Our system allows the user to interactively create various fluid animations from a single set of velocity fields generated by the fluid simulation. In a preprocess, our method converts the input velocity fields into scalar fields representing the stream functions. At run-time, the user deforms the grid representing the scalar stream functions and the deformed velocity fields are then obtained by applying a curl operator to the deformed scalar stream functions. The velocity fields obtained by this process naturally perseveres the divergence-free condition. For the deformation of the grid, we use a method based on Moving Least Squares. The usefulness of our method is demonstrated by several examples.
  • An Optimization Approach for Designing Fluid Flow Fields
    Syuhei Sato, Yoshinori Dobashi, Kei Iwasaki, Hiroyuki Ochiai, Tsuyoshi Yamamoto, Tomoyuki Nishita
    Computer Graphics International 2014 short paper 2014/06 [Refereed][Not invited]
  • Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita
    ACM TRANSACTIONS ON GRAPHICS 33 (3) 31:1-31:7  0730-0301 2014/05 [Refereed][Not invited]
     
    We present a technique for computing the shape of a transparent object that can generate user-defined caustic patterns. The surface of the object generated using our method is smooth. Thanks to this property, the resulting caustic pattern is smooth, natural, and highly detailed compared to the results obtained using previous methods. Our method consists of two processes. First, we use a differential geometry approach to compute a smooth mapping between the distributions of the incident light and the light reaching the screen. Second, we utilize this mapping to compute the surface of the object. We solve Poisson's equation to compute both the mapping and the surface of the object.
  • Syuhei Sato, Yoshinori Dobashi, Kei Iwasaki, Hiroyuki Ochiai, Tsuyoshi Yamamoto, Tomoyuki Nishita
    ACM SIGGRAPH 2014 Posters, SIGGRAPH 2014 9:1  2014 [Refereed][Not invited]
  • Mikio Shinya, Yoshinori Dobashi, Kei Iwasaki, Michio Shiraishi, Tomoyuki Nishita
    Journal of Information Processing 21 (2) 349 - 357 0387-5806 2013/04 [Refereed][Not invited]
     
    Fast computation of multiple reflections and scattering among complex objects is very important in photorealistic rendering. This paper applies the plane-parallel scattering theory to the rendering of densely distributed objects such as trees. We propose a simplified plane-parallel scattering model that has very simple analytic solutions, allowing efficient evaluation of multiple scattering. A geometric compensation method is also introduced to cope with the infinite plane condition, required by the plane-parallel model. The scattering model was successfully applied to tree rendering. Comparison with a Monte Carlo method was made and reasonable agreement was confirmed. A rendering system based on the model was implemented and multiple inter-reflections were effectively obtained. The view-independent feature of the model allows fast display of scenes. The pre-computation is also modest, permitting interactive control of lighting conditions. © 2013 Information Processing Society of Japan.
  • Shinya Mikio, Dobashi Yoshinori, Iwasaki Kei, Shiraishi Michio, Nishita Tomoyuki
    IMT Information and Media Technologies Editorial Board 8 (2) 380 - 388 1881-0896 2013 
    Fast computation of multiple reflections and scattering among complex objects is very important in photorealistic rendering. This paper applies the plane-parallel scattering theory to the rendering of densely distributed objects such as trees. We propose a simplified plane-parallel scattering model that has very simple analytic solutions, allowing efficient evaluation of multiple scattering. A geometric compensation method is also introduced to cope with the infinite plane condition, required by the plane-parallel model. The scattering model was successfully applied to tree rendering. Comparison with a Monte Carlo method was made and reasonable agreement was confirmed. A rendering system based on the model was implemented and multiple inter-reflections were effectively obtained. The view-independent feature of the model allows fast display of scenes. The pre-computation is also modest, permitting interactive control of lighting conditions.
  • Syuhei Sato, Yoshinori Dobashi, Kei Iwasaki, Hiroyuki Ochiai, Tsuyoshi Yamamoto
    SIGGRAPH Asia 2013 Technical Briefs, SA 2013 13:1-13:4  2013 [Refereed][Not invited]
     
    The visual simulation of fluids has become an important element in many applications, such as movies and computer games. In these applications, large-scale fluid scenes, such as fire in a village, are often simulated by repeatedly rendering multiple small-scale fluid flows. In these cases, animators are requested to generate many variations of a small-scale fluid flow. This paper presents a method to help animators meet such requirements. Our method enables the user to generate flow field variations from a single simulated dataset obtained by fluid simulation. The variations are generated in both the frequency and spatial domains. Fluid velocity fields are represented using Laplacian eigenfunctions which ensure that the flow field is always incompressible. In generating the variations in the frequency domain, we modulate the coefficients (amplitudes) of the basis functions. To generate variations in the spatial domain, our system expands or contracts the simulation space, then the flow is calculated by solving a minimization problem subject to the resized velocity field. Using our method, the user can easily create various animations from a single dataset calculated by fluid simulation. 2013 Copyright held by the Owner/Author.
  • Wataru Naya, Kazuya Fukumoto, Tsuyoshi Yamamoto, Yoshinori Dobashi
    SUI 2013 - Proceedings of the ACM Symposium on Spatial User Interaction 93  2013 [Refereed][Not invited]
     
    We propose a real-time image-based animation technique for virtual fitting applications. Our method uses key image finding from a database which uses skeletal data as a search key, and then create in-between images by using image morphing. Comparing to conventional method using 3DCG rendering, our method achieves higher frame rate and realistic textile representation. Unlike [1], data size and search time are reduced with database optimization. Copyright © ACM 2013.
  • Hisanari Otsu, Yonghao Yue, Qiming Hou, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    ACM SIGGRAPH 2013 Posters, SIGGRAPH 2013 106  2013 [Refereed][Not invited]
     
    Developing a robust method for computing global illumination is a challenging problem. A Markov chain Monte Carlo (MCMC) method, like [Jakob and Marschner 2012], samples the light path space with a probability proportional to the per-path contribution, by successively mutating path samples (e.g., perturbing a reflection direction). In practice, a path sample could get stuck in a high energy peak for multiple mutations, resulting in a bright spot artifact. To resolve this problem, we present a new unbiased rendering framework based on a replica exchange technique [Kitaoka et al. 2009], a variant of MCMC technique. A replica exchange technique incorporates a set of different distributions. We propose to introduce a set of relaxed distributions, which are beneficial for reducing the chance of getting stuck.
  • Tomokazu Ishikawa, Yoshinori Dobashi, Yonghao Yue, Masanori Kakimoto, Taichi Watanabe, Kunio Kondo, Kei Iwasaki, Tomoyuki Nishita
    Special Interest Group on Computer Graphics and Interactive Techniques Conference, SIGGRAPH '13, Anaheim, CA, USA, July 21-25, 2013, Poster Proceedings 14 - 14 2013 [Refereed][Not invited]
  • Kosuke Nabata, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    High-Performance Graphics 2013, Anaheim, California, USA, July 19-21, 2013. Proceedings ACM 129 - 136 2013 [Refereed][Not invited]
  • Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    ACM TRANSACTIONS ON GRAPHICS 31 (6) Article 144  0730-0301 2012/11 [Refereed][Not invited]
     
    We present a new technique for bi-scale material editing using Spherical Gaussians (SGs). To represent large-scale appearances, an effective BRDF that is the average reflectance of small-scale details is used. The effective BRDF is calculated from the integral of the product of the Bidirectional Visible Normal Distribution (BVNDF) and BRDFs of small-scale geometry. Our method represents the BVNDF with a sum of SGs, which can be calculated on-the-fly, enabling interactive editing of small-scale geometry. By representing small-scale BRDFs with a sum of SGs, effective BRDFs can be calculated analytically by convolving the SGs for BVNDF and BRDF. We propose a new SG representation based on convolution of two SGs, which allows real-time rendering of effective BRDFs under all-frequency environment lighting and real-time editing of small-scale BRDFs. In contrast to the previous method, our method does not require extensive precomputation time and large volume of precomputed data per single BRDF, which makes it possible to implement our method on a GPU, resulting in real-time rendering.
  • Yoshinori Dobashi, Wataru Iwasaki, Ayumi Ono, Tsuyoshi Yamamoto, Yonghao Yue, Tomoyuki Nishita
    ACM TRANSACTIONS ON GRAPHICS 31 (6) Article 145  0730-0301 2012/11 [Refereed][Not invited]
     
    Clouds play an important role in creating realistic images of outdoor scenes. Many methods have therefore been proposed for displaying realistic clouds. However, the realism of the resulting images depends on many parameters used to render them and it is often difficult to adjust those parameters manually. This paper proposes a method for addressing this problem by solving an inverse rendering problem: given a non-uniform synthetic cloud density distribution, the parameters for rendering the synthetic clouds are estimated using photographs of real clouds. The objective function is defined as the difference between the color histograms of the photograph and the synthetic image. Our method searches for the optimal parameters using genetic algorithms. During the search process, we take into account the multiple scattering of light inside the clouds. The search process is accelerated by precomputing a set of intermediate images. After ten to twenty minutes of precomputation, our method estimates the optimal parameters within a minute.
  • Yoshinori Dobashi, Wataru Iwasaki, Ayumi Ono, Tsuyoshi Yamamoto, Yonghao Yue, Tomoyuki Nishita
    ACM TRANSACTIONS ON GRAPHICS 31 (6) 145  0730-0301 2012/11 [Refereed][Not invited]
     
    Clouds play an important role in creating realistic images of outdoor scenes. Many methods have therefore been proposed for displaying realistic clouds. However, the realism of the resulting images depends on many parameters used to render them and it is often difficult to adjust those parameters manually. This paper proposes a method for addressing this problem by solving an inverse rendering problem: given a non-uniform synthetic cloud density distribution, the parameters for rendering the synthetic clouds are estimated using photographs of real clouds. The objective function is defined as the difference between the color histograms of the photograph and the synthetic image. Our method searches for the optimal parameters using genetic algorithms. During the search process, we take into account the multiple scattering of light inside the clouds. The search process is accelerated by precomputing a set of intermediate images. After ten to twenty minutes of precomputation, our method estimates the optimal parameters within a minute.
  • Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    ACM Transactions on Graphics 31 (6) 144  0730-0301 2012/11 [Refereed][Not invited]
     
    We present a new technique for bi-scale material editing using Spherical Gaussians (SGs). To represent large-scale appearances, an effective BRDF that is the average reflectance of small-scale details is used. The effective BRDF is calculated from the integral of the product of the Bidirectional Visible Normal Distribution (BVNDF) and BRDFs of small-scale geometry. Our method represents the BVNDF with a sum of SGs, which can be calculated on-the-fly, enabling interactive editing of small-scale geometry. By representing small-scale BRDFs with a sum of SGs, effective BRDFs can be calculated analytically by convolving the SGs for BVNDF and BRDF. We propose a new SG representation based on convolution of two SGs, which allows real-time rendering of effective BRDFs under all-frequency environment lighting and real-time editing of small-scale BRDFs. In contrast to the previous method, our method does not require extensive precomputation time and large volume of precomputed data per single BRDF, which makes it possible to implement our method on a GPU, resulting in real-time rendering. © 2012 ACM.
  • Wataru Furuya, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    IPSJ Journal 一般社団法人情報処理学会 53 (7) 1905 - 1914 0387-5806 2012/07/15 [Not refereed][Not invited]
     
    We propose a real-time rendering method for dynamic scenes under all-frequency environmental lighting. To render the object surfaces illuminated by environmental lighting, the product of the environmental lighting, the visibility function at each shading point on the object surfaces, and the BRDF is integrated. Our method represents the environmental lighting and the BRDFs with spherical Gaussians and represents the visibility functions with spherical signed distance functions (SSDFs). Although these representations enable us to render scenes under all-frequency lighting in real-time, the p...
  • Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita
    COMPUTER GRAPHICS FORUM 31 (2) 575 - 582 0167-7055 2012/05 [Refereed][Not invited]
     
    Pixel art is a kind of digital art that through per-pixel manipulation enables production of a diverse array of artistic images. In this paper, we present a new way for people to experience and express pixel art. Our digital art consists of a set of sticks made of acrylate resin, each of which refracts light from a parallel light source, in certain directions. Artistic users are able to easily rearrange these sticks and view their digital art through the refracted light projection on any planar surface. As we demonstrate in this paper, a user can generate various artistic images using only a single set of sticks. We additionally envision that our pixel art with rearrangeable sticks would have great entertainment appeal, e. g., as an art puzzle.
  • Kei Iwasaki, Wataru Furuya, Yoshinori Dobashi, Tomoyuki Nishita
    COMPUTER GRAPHICS FORUM 31 (2) 727 - 734 0167-7055 2012/05 [Refereed][Not invited]
     
    We propose an efficient rendering method for dynamic scenes under all-frequency environmental lighting. To render the surfaces of objects illuminated by distant environmental lighting, the triple product of the lighting, the visibility function and the BRDF is integrated at each shading point on the surfaces. Our method represents the environmental lighting and the BRDF with a linear combination of spherical Gaussians, replacing the integral of the triple product with the sum of the integrals of spherical Gaussians over the visible region of the hemisphere. We propose a new form of spherical Gaussian, the integral spherical Gaussian, that enables the fast and accurate integration of spherical Gaussians with various sharpness over the visible region on the hemisphere. The integral spherical Gaussian simplifies the integration to a sum of four pre-integrated values, which are easily evaluated on-the-fly. With a combination of a set of spheres to approximate object geometries and the integral spherical Gaussian, our method can render object surfaces very efficiently. Our GPU implementation demonstrates real-time rendering of dynamic scenes with dynamic viewpoints, lighting, and BRDFs.
  • Kei Iwasaki, Wataru Furuya, Yoshinori Dobashi, Tomoyuki Nishita
    COMPUTER GRAPHICS FORUM 31 (2) 727 - 734 0167-7055 2012/05 [Refereed][Not invited]
     
    We propose an efficient rendering method for dynamic scenes under all-frequency environmental lighting. To render the surfaces of objects illuminated by distant environmental lighting, the triple product of the lighting, the visibility function and the BRDF is integrated at each shading point on the surfaces. Our method represents the environmental lighting and the BRDF with a linear combination of spherical Gaussians, replacing the integral of the triple product with the sum of the integrals of spherical Gaussians over the visible region of the hemisphere. We propose a new form of spherical Gaussian, the integral spherical Gaussian, that enables the fast and accurate integration of spherical Gaussians with various sharpness over the visible region on the hemisphere. The integral spherical Gaussian simplifies the integration to a sum of four pre-integrated values, which are easily evaluated on-the-fly. With a combination of a set of spheres to approximate object geometries and the integral spherical Gaussian, our method can render object surfaces very efficiently. Our GPU implementation demonstrates real-time rendering of dynamic scenes with dynamic viewpoints, lighting, and BRDFs.
  • Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita
    COMPUTER GRAPHICS FORUM 31 (2) 575 - 582 0167-7055 2012/05 [Refereed][Not invited]
     
    Pixel art is a kind of digital art that through per-pixel manipulation enables production of a diverse array of artistic images. In this paper, we present a new way for people to experience and express pixel art. Our digital art consists of a set of sticks made of acrylate resin, each of which refracts light from a parallel light source, in certain directions. Artistic users are able to easily rearrange these sticks and view their digital art through the refracted light projection on any planar surface. As we demonstrate in this paper, a user can generate various artistic images using only a single set of sticks. We additionally envision that our pixel art with rearrangeable sticks would have great entertainment appeal, e. g., as an art puzzle.
  • IWASAKI Wataru, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi
    The IEICE transactions on information and systems (Japanese edetion) 一般社団法人電子情報通信学会 95 (2) 297 - 304 1880-4535 2012/02/01 [Not refereed][Not invited]
     
    コンピュータグラフィックスにおいて,雲は屋外シーンを構成する重要な要素の一つである.そのため,雲のレンダリングに関してこれまで多くの研究が行われてきた.しかし,雲のレンダリング結果は多くのパラメータに依存し,ユーザが所望する結果を直感的に生成することは容易ではない.そこで,本論文では,雲のボリュームレンダリングにおけるパラメータを直感的に指定することで,所望のレンダリング結果が容易に得られるシステムを提案する.提案システムでは,ユーザは,レンダリングパラメータを直接指定するのではなく,より直感的な操作により間接的に指定する.提案システムを用いることで,ユーザは雲の輝度計算式に関する知識が無くとも,容易に所望のボリュームレンダリング結果を生成することが可能である.
  • Takanori Nishino, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    SIGGRAPH Asia 2012 Technical Briefs, SA 2012 2012 [Refereed][Not invited]
     
    Ice often contains small air bubbles that are dissolved air exhausted from water-ice interface. Depicting these air bubbles with various sizes enhances the realism of ice. This paper proposes a fast simulation method of freezing ice taking into account air bubbles. Our method introduces a physically-based calculation method of the sizes of air bubbles based on the freezing velocity and pressure. In contrast to the previous method, our method can represent numerous small bubbles that cannot be represented by using the resolutions of simulation grids. The computations of heat transfer, tracking of water-ice interface, and generation of bubbles are accelerated by implementing our method using CUDA. Our method achieves the freezing simulation and bubble generation at interactive frame-rates. © 2012 ACM.
  • Syuhei Sato, Takuya Morita, Yoshinori Dobashi, Tsuyoshi Yamamoto
    Proceedings - Digital Production Symposium 2012, DigiPro 2012 37 - 42 2012 [Refereed][Not invited]
     
    We propose a simple and efficient data-driven method for synthesizing high-resolution 3D animations of fire from low-resolution fluid simulations. Our method is based on grid-based fluid simulation. The key concept behind our method is to use a precomputed database of high-resolution velocity fields in order to produce small-scale details that are lost in low-resolution velocity fields. The database is constructed by 2D fluid simulation and no highresolution 3D fluid simulations need to be executed. At run-time, a low-resolution 3D fluid simulation is executed and the velocity field calculated at each time step is approximated by a linear combination of the precomputed velocity fields. This approximation process produces realistic small-scale detail. Using our method, users can efficiently design animations of fire with low-resolution simulation and our method converts them into high-resolution animations. We examine the ability of our method by applying it to simulations of fire under various situations including moving obstacles. Copyright © 2012 by the Association for Computing Machinery, Inc.
  • Tomokazu Ishikawa, Yonghao Yue, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    Computer Vision, Imaging and Computer Graphics. Theory and Application - 7th International Joint Conference, VISIGRAPP 2012, Rome, Italy, February 24-26, 2012, Revised Selected Papers 112 - 126 2012 [Refereed][Not invited]
  • Mumehiro Tada, Yoshinori Dobashi, Tsuyoshi Yamamoto
    Proceedings - VRCAI 2012: 11th ACM SIGGRAPH International Conference on Virtual-Reality Continuum and Its Applications in Industry 47 - 50 2012 [Refereed][Not invited]
     
    In computer graphics, shading techniques play an important role when displaying realistic virtual objects. Although physically-based techniques can generate realistic results, it is often difficult to produce desired shading effects. Therefore, artists usually creates desired shading effects by manually placing many virtual light sources. However, this is not an easy task since it is difficult to predict the shading effects obtained by those virtual light sources. We propose an intuitive system that allows a user to produce the desired shading effects. In our system, the user can directly specify the desired intensities at arbitrary positions on the surfaces of objects. The desired shading effects are realized by our feature-based interpolation of the specified intensities. © 2012 ACM.
  • Xiaoxiong Xing, Yoshinori Dobashi, Tsuyoshi Yamamoto, Yosuke Katsura, Ken Anjyo
    SIGGRAPH Asia 2012 Posters, SA 2012 43 - 46 2012 [Refereed][Not invited]
     
    We present a fast algorithm for the interactive rendering of animated hair under a dynamic lighting environment. Previous methods use spherical radial basis functions (SRBF) for efficient evaluation of the rendering equation for hair [Ren et al. 2010]. However, this method is not suitable for dynamic lighting environments, since it requires a high computational cost to approximate environmental light using SRBFs. We address this problem by using spherical harmonics (SH) to approximate both the transmittance and the environmental light. Since SH functions are orthogonal, the environmental light is efficiently converted into an SH representation. However, to obtain an SH representation of the transmittance for animated hair, we need to compute the transmittance for all directions at each vertex at each frame, which is very time-consuming. Our method reduces the computational cost by using a voxel-based approach to compute the transmittances. Copyright is held by the author / owner(s).
  • Xiaoxiong Xing, Yoshinori Dobashi, Tsuyoshi Yamamoto, Yosuke Katsura, Ken Anjyo
    SIGGRAPH Asia 2012 Posters, SA 2012 40  2012 [Refereed][Not invited]
     
    We present a fast algorithm for the interactive rendering of animated hair under a dynamic lighting environment. Previous methods use spherical radial basis functions (SRBF) for efficient evaluation of the rendering equation for hair [Ren et al. 2010]. However, this method is not suitable for dynamic lighting environments, since it requires a high computational cost to approximate environmental light using SRBFs. We address this problem by using spherical harmonics (SH) to approximate both the transmittance and the environmental light. Since SH functions are orthogonal, the environmental light is efficiently converted into an SH representation. However, to obtain an SH representation of the transmittance for animated hair, we need to compute the transmittance for all directions at each vertex at each frame, which is very time-consuming. Our method reduces the computational cost by using a voxel-based approach to compute the transmittances. Copyright is held by the author / owner(s).
  • Katsutoshi Kusumoto, Yoshinori Dobashi, Tsuyoshi Yamamoto
    SIGGRAPH Asia 2012 Posters, SA 2012 4  2012 [Refereed][Not invited]
     
    Clouds play an important role when creating realistic images of out-door scenes. One of the most effective approaches for synthesizing realistic clouds is to simulate the cloud formation processes based on fluid dynamics. However, the resulting shapes of clouds de- pend on many simulation parameters. Therefore, it is difficult to adjust those parameters so that the clouds form the desired shapes. This paper presents a new method for controlling the simulation of cloud formation. Although there are various types of clouds, we fo-cus here on cumulus clouds. By using our method, cumulus clouds that change into specified shapes can be animated without repeating simulations using various parameter-values determined by trial and error. Copyright is held by the author / owner(s).
  • Tomokazu Ishikawa, Yonghao Yue, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    GRAPP & IVAPP 2012: Proceedings of the International Conference on Computer Graphics Theory and Applications and International Conference on Information Visualization Theory and Applications, Rome, Italy, 24-26 February, 2012 319 - 327 2012 [Refereed][Not invited]
  • Syuhei Sato, Yoshinori Dobashit, Tsuyoshi Yamamoto, Ken Anjyo
    Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers The Institute of Image Information and Television Engineers 65 (10) 1446 - 1451 1342-6907 2011/10 [Not refereed][Not invited]
     
    Recently, many methods for simulating natural phenomena on the basis of fluid simulation have been proposed. A method for simulating explosions was also proposed, but the shapes of the simulated explosions depend on many simulation parameters. Therefore, creating the desired shape for an explosion as specified by the user is difficult. In this paper, we propose a method for controlling explosion simulations in order to form the desired shapes. Our method optimizes the initial intensity distribution of an explosion and controls the simulation to minimize the difference between the target shape and the shape of the simulated explosion. We use a predictive approach to control the explosion simulation accurately. Using the proposed method, animations of explosions controlled into specified shapes can be generated.
  • Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita
    COMPUTER GRAPHICS FORUM 30 (7) 1911 - 1919 0167-7055 2011/09 [Refereed][Not invited]
     
    Photo-realistic rendering of inhomogeneous participating media with light scattering in consideration is important in computer graphics, and is typically computed using Monte Carlo based methods. The key technique in such methods is the free path sampling, which is used for determining the distance (free path) between successive scattering events. Recently, it has been shown that efficient and unbiased free path sampling methods can be constructed based on Woodcock tracking. The key concept for improving the efficiency is to utilize space partitioning (e.g., kd-tree or uniform grid), and a better space partitioning scheme is important for better sampling efficiency. Thus, an estimation framework for investigating the gain in sampling efficiency is important for determining how to partition the space. However, currently, there is no estimation framework that works in 3D space. In this paper, we propose a new estimation framework to overcome this problem. Using our framework, we can analytically estimate the sampling efficiency for any typical partitioned space. Conversely, we can also use this estimation framework for determining the optimal space partitioning. As an application, we show that new space partitioning schemes can be constructed using our estimation framework. Moreover, we show that the differences in the performances using different schemes can be predicted fairly well using our estimation framework.
  • Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita
    COMPUTER GRAPHICS FORUM 30 (7) 1911 - 1919 0167-7055 2011/09 [Refereed][Not invited]
     
    Photo-realistic rendering of inhomogeneous participating media with light scattering in consideration is important in computer graphics, and is typically computed using Monte Carlo based methods. The key technique in such methods is the free path sampling, which is used for determining the distance (free path) between successive scattering events. Recently, it has been shown that efficient and unbiased free path sampling methods can be constructed based on Woodcock tracking. The key concept for improving the efficiency is to utilize space partitioning (e.g., kd-tree or uniform grid), and a better space partitioning scheme is important for better sampling efficiency. Thus, an estimation framework for investigating the gain in sampling efficiency is important for determining how to partition the space. However, currently, there is no estimation framework that works in 3D space. In this paper, we propose a new estimation framework to overcome this problem. Using our framework, we can analytically estimate the sampling efficiency for any typical partitioned space. Conversely, we can also use this estimation framework for determining the optimal space partitioning. As an application, we show that new space partitioning schemes can be constructed using our estimation framework. Moreover, we show that the differences in the performances using different schemes can be predicted fairly well using our estimation framework.
  • Hiroyuki Kubo, Yoshinori Dobashi, Shigeo Morishima
    The International Journal of Virtual Reality 10 (1) 41 - 47 2011/05 [Refereed][Not invited]
  • EGUCHI Yukihisa, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi, IWASAKI Kei
    The Transactions of the Institute of Electronics, Information and Communication Engineers. A 一般社団法人電子情報通信学会 94 (1) 30 - 36 0913-5707 2011/01/01 [Not refereed][Not invited]
     
    本論文では,動的な雲を効率的にレンダリングする手法を提案する.屋外景観のアニメーション映像を作成する場合,時々刻々と変化する雲の映像を作成する必要がある.このとき,リアルな映像作成のためには,雲の三次元密度分布を考慮した表示が求められる.しかし,動的な雲に対して毎フレーム輝度計算を行って画像生成を行うことは計算コストが高い点が問題となる.そこで,本研究では,この問題を解決するため,前もって有限時間の長さの動的な雲のデータベースを用意しておく手法を提案する.このデータベースを利用して,太陽位置や視点位置にかかわらず,任意の長さの動的な雲の映像を高速に生成する.動的な雲のボリュームデータは,Video Textureと呼ばれる動的なテクスチャを合成する手法を利用して生成する.また,Spherical Harmonic Exponentiationを応用することで高速レンダリングを実現する.提案法により,太陽直接光及び天空光に照射された動的な雲の効率的な表示が可能である.
  • Tomokazu Ishikawa, Yonghao Yue, Tomoyuki Nishita, Yoshinori Dobashi
    Journal of the Institute of Image Electronics Engineers of Japan 40 (1) 141 - 150 1348-0316 2011 [Not refereed][Not invited]
     
    We propose an efficient method based on physical laws to model phenomena near the surface of the sun, which is known as the solar photosphere. In the field of astronomy, some physical models have been developed to simulate the sun's turbulence. Most of the previous models are difficult to be applied in the making of CG images since they require a considerable amount of time even when using a supercomputer. The subject of our research is the visual simulation of the phenomena observed above the photosphere, namely solar prominences, because these are characteristic phenomena of the sun that can greatly influence the visual impact in movies and games. The sun is mainly composed of ionized plasma, and its behavior can be treated as a fluid. However, unlike gas, the plasma fluid is influenced by the magnetic field. Thus, magnetic field calculations are needed to calculate the plasma behavior. We use the magnetohydrodynamics (MHD) equations to simulate the behavior of plasma. We propose a new method which can simulate a prominence in a practical computation time. The computation cost is reduced by simplifying the phenomena inside the sun: we only consider the phenomena after the solar prominence erupts because the phenomena before the eruption dose not manifest itself in a visual way. To render the simulation results, we emulate an observation method that extracts the specific spectrum emission from the solar plasma. © 2011, The Institute of Image Electronics Engineers of Japan. All rights reserved.
  • Ayumi Ono, Yoshinori Dobashi, Tsuyoshi Yamamoto
    SIGGRAPH Asia 2011 Sketches, SA'11 2011 [Refereed][Not invited]
     
    Synthetic images of outdoor scenes generated by computer graphics usually contain the sky as background. The appearance of the sky plays an important role in enhancing the reality of scenes. In this paper, we propose an intuitive and interactive system for synthesizing sky images that can reflect the user's intention. Our system consists of two steps. The first step is a sky generation step. The luminance distribution and colors of the sky are generated using our intuitive user interface. The second step is a cloud composition step. We have prepared a database of photographs of real clouds. Our system searches the database for cloud photographs that are suitable for the synthesized sky. The user selects the clouds in the search results and they are composited into the sky image. By using our system, the user can easily generate desired sky images.
  • Wataru Furuya, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    SIGGRAPH Asia 2011 Sketches, SA'11 2011 [Refereed][Not invited]
     
    Real-time rendering of dynamic scenes illuminated by complex, all-frequency lighting with highly glossy BRDFs remains a challenging problem. Although several methods have been proposed to render dynamic scenes, these methods can not handle deformable objects [Zhou et al. 2005], all-frequency lighting [Ren et al. 2006 Nowrouzezahrai et al. 2009], or highly glossy BRDFs [Annen et al. 2008].
  • Tomokazu Ishikawa, Yonghao Yue, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    Spring Conference on Computer Graphics, SCCG '11, Vininé, Slovakia, April 28-30, 2011 13 - 16 2011 [Refereed][Not invited]
  • Hiroyuki Kubo, Yoshinori Dobashi, Shigeo Morishima
    HUMAN INTERFACE AND THE MANAGEMENT OF INFORMATION: INTERACTING WITH INFORMATION, PT 2 6772 388 - 395 0302-9743 2011 [Refereed][Not invited]
     
    To synthesize a realistic human animation using computer graphics, it is necessary to simulate subsurface scattering inside a human skin. We have developed a curvature-dependent reflectance functions (CDRF) which mimics the presence of a subsurface scattering effect. In this approach, we provide only a single parameter that represents the intensity of incident light scattering in a translucent material. We implemented our algorithm as a hardware-accelerated real-time renderer with a HLSL pixel shader. This approach is easily implementable on the GPU and does not require any complicated pre-processing and multi-pass rendering as is often the case in this area of research.
  • Syuhei Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto, Ken Anjyo
    Proceedings - 12th International Conference on Computer-Aided Design and Computer Graphics, CAD/Graphics 2011 296 - 301 2011 [Refereed][Not invited]
     
    This paper presents a method for controlling simulated explosions by prediction and optimization. Many methods have been proposed for simulating realistic explosion based on numerical fluid analysis. These methods are widely used in applications such as movies and computer games. In these applications, there is often a requirement for the explosion to conform to a specified final shape. The goal of our research is to meet this requirement by controlling the simulation so that the explosion evolves into a target shape specified by the user. The key ideas of our method are optimization of the initial velocities at the explosion source and predictive control of the simulation. Our method optimizes the initial velocities during the preprocessing step. Next, during the simulation, it predicts the future shape from the history of the explosion shape and controls the simulation to minimize the difference between the target shape and the predicted shape. © 2011 IEEE.
  • Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita
    ACM TRANSACTIONS ON GRAPHICS 29 (6) Article 177  0730-0301 2010/12 [Refereed][Not invited]
     
    Realistic rendering of participating media is one of the major subjects in computer graphics. Monte Carlo techniques are widely used for realistic rendering because they provide unbiased solutions, which converge to exact solutions. Methods based on Monte Carlo techniques generate a number of light paths, each of which consists of a set of randomly selected scattering events. Finding a new scattering event requires free path sampling to determine the distance from the previous scattering event, and is usually a time-consuming process for inhomogeneous participating media. To address this problem, we propose an adaptive and unbiased sampling technique using kd-tree based space partitioning. A key contribution of our method is an automatic scheme that partitions the spatial domain into sub-spaces (partitions) based on a cost model that evaluates the expected sampling cost. The magnitude of performance gain obtained by our method becomes larger for more inhomogeneous media, and rises to two orders compared to traditional free path sampling techniques.
  • Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita
    ACM TRANSACTIONS ON GRAPHICS 29 (6) 177  0730-0301 2010/12 [Refereed][Not invited]
     
    Realistic rendering of participating media is one of the major subjects in computer graphics. Monte Carlo techniques are widely used for realistic rendering because they provide unbiased solutions, which converge to exact solutions. Methods based on Monte Carlo techniques generate a number of light paths, each of which consists of a set of randomly selected scattering events. Finding a new scattering event requires free path sampling to determine the distance from the previous scattering event, and is usually a time-consuming process for inhomogeneous participating media. To address this problem, we propose an adaptive and unbiased sampling technique using kd-tree based space partitioning. A key contribution of our method is an automatic scheme that partitions the spatial domain into sub-spaces (partitions) based on a cost model that evaluates the expected sampling cost. The magnitude of performance gain obtained by our method becomes larger for more inhomogeneous media, and rises to two orders compared to traditional free path sampling techniques.
  • KUBO Hiroyuki, DOBASHI Yoshinori, MORISHIMA Shigeo
    The Transactions of the Institute of Electronics, Information and Communication Engineers. A 一般社団法人電子情報通信学会 93 (11) 708 - 717 0913-5707 2010/11/01 [Not refereed][Not invited]
     
    CGを用いて人間の肌や大理石に代表される半透明物体を表現するために,物体内部で生じる表面下散乱現象を考慮することは有効な手段といえる.しかし表面下散乱の物理的に正確なモデル化には,大域照明モデルを導入せざるを得ず,実時間でのレンダリングにはほど遠いのが現状である.表面下散乱による影響は,物体表面の起伏の激しい点において特に顕著であると考えられる.そこで本研究では物体表面の起伏の強さを表す指標として,曲率を導入する.曲率は物体表面上で局所的に決定されるパラメータであるため,局所照明モデルが適用可能であり,高速なレンダリングが実現される.まず与えられた物体と同じ物質パラメータを有する半径γの球について,単一の白色な平行光源下で球表面の放射輝度分布を推定する.半径rの球面の曲率は1/rで表されるため,様々な半径の球面に対する放射輝度分布を調査することにより,曲率κ,光源と法線とのなす角θ_iに対する反射関数g_r(θ_i,κ)をルックアップテーブル(LUT)として取得する.レンダリング時にはあらかじめ曲率が計算されたポリゴンモデルに対し,LUTをテクスチャとして参照することで,リアルタイムに表面下散乱の影響を考慮したレンダリングが可能となる.
  • Yusuke Tsuda, Yonghao Yue, Yoshinori Dobashi, Tomoyuki Nishita
    VISUAL COMPUTER 26 (6-8) 883 - 891 0178-2789 2010/06 [Refereed][Not invited]
     
    In the field of computer graphics, simulation of fluids, including avalanches, is an important research topic. In this paper, we propose a method to simulate a kind of avalanche, mixed-motion avalanche, which is usually large and travels down the slope fast, often resulting in impressive visual effects. The mixed-motion avalanche consists of snow smokes and liquefied snow which form an upper suspension layer and a lower dense-flow layer, respectively. The mixed-motion avalanche travels down the surface of the snow-covered mountain, which is called accumulated snow layer. We simulate a mixed-motion avalanche taking into account these three snow layers. We simulate the suspension layer using a grid-based approach, the dense-flow and accumulated snow layer using a particle-based approach. An important contribution of our method is an interaction model between these snow layers that enables us to obtain the characteristic motions of avalanches, such as the generation of the snow smoke from the head of the avalanche.
  • Yoshinori Dobashi, Tsuyoshi Yamamoto, Tomoyuki Nishita
    SCIENCE CHINA-INFORMATION SCIENCES 53 (5) 920 - 931 1674-733X 2010/05 [Refereed][Not invited]
     
    This paper presents an interactive system for realistic visualization of earth-scale clouds. Realistic images can be generated at interactive frame rates while the viewpoint and the sunlight directions can be changed interactively. The realistic display of earth-scale clouds requires us to render large volume data representing the density distribution of the clouds. However, this is generally time-consuming and it is difficult to achieve the interactive performance, especially when the sunlight direction can be changed. To address this, our system precomputes the integrated intensities and opacities of clouds for various viewing and sunlight directions. This idea is combined with a novel hierarchical data structure for further acceleration. The photorealism of the final image is improved by taking into account the atmospheric effects and shadows of clouds on the earth. We demonstrate the usefulness of our system by an application to a space flight simulation.
  • Yoshinori Dobashi, Yusuke Shinzo, Tsuyoshi Yamamoto
    COMPUTER GRAPHICS FORUM 29 (7) 2083 - 2090 0167-7055 2010 [Refereed][Not invited]
     
    In this paper, we propose a simple method for modeling clouds from a single photograph. Our method can synthesize three types of clouds: cirrus, altocumulus, and cumulus. We use three different representations for each type of cloud: two-dimensional texture for cirrus, implicit functions (metaballs) for altocumulus, and volume data for cumulus. Our method initially computes the intensity and the opacity of clouds for each pixel from an input photograph, stored as a cloud image. For cirrus, the cloud image is the output two-dimensional texture. For each of the other two types of cloud, three-dimensional density distributions are generated by referring to the cloud image. Since the method is very simple, the computational cost is low. Our method can generate, within several seconds, realistic clouds that are similar to those in the photograph.
  • Mikio Shinya, Mishio Shiraishi, Yoshinori Dobashi, Kei Iwasaki, Tomoyuki Nishita
    Proceedings - Pacific Conference on Computer Graphics and Applications 85 - 92 1550-4085 2010 [Refereed][Not invited]
     
    Fast computation of multiple light reflections and scattering among complex objects is very important in photorealistic rendering. This paper applies the plane-parallel scattering theory to the rendering of densely distributed objects such as hairs. We propose a simplified plane-parallel model that has very simple analytic solutions. This allows us to deal with multiple scattering phenomena in hair under ambient and area light illumination. The model was successfully applied to hair rendering, and experiments demonstrated the efficiency of the proposed method. © 2010 IEEE.
  • Yoshinori Dobashi, Tsuyoshi Yamamoto, Tomoyuki Nishita
    Science in China, Series F: Information Sciences 53 (5) 920 - 931 1009-2757 2010 [Refereed][Not invited]
     
    This paper presents an interactive system for realistic visualization of earth-scale clouds. Realistic images can be generated at interactive frame rates while the viewpoint and the sunlight directions can be changed interactively. The realistic display of earth-scale clouds requires us to render large volume data representing the density distribution of the clouds. However, this is generally time-consuming and it is difficult to achieve the interactive performance, especially when the sunlight direction can be changed. To address this, our system precomputes the integrated intensities and opacities of clouds for various viewing and sunlight directions. This idea is combined with a novel hierarchical data structure for further acceleration. The photorealism of the final image is improved by taking into account the atmospheric effects and shadows of clouds on the earth. We demonstrate the usefulness of our system by an application to a space flight simulation. © 2010 Science China Press and Springer-Verlag Berlin Heidelberg.
  • Hiroyuki Kubo, Yoshinori Dobashi, Shigeo Morishima
    ACM SIGGRAPH 2010 Talks, SIGGRAPH '10 a46  2010 [Refereed][Not invited]
     
    Simulating sub-surface scattering is one of the most effective ways for realistically synthesizing translucent materials such as marble, milk and human skin. In previous work, the method developed by Jensen et al. [2002] significantly improved the speed of the simulation. However, the process is still not fast enough to produce realtime rendering. Thus, we have developed a curvature-dependent reflectance function (CDRF) which mimics the presence of a subsurface scattering effect.
  • Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    2010 INTERNATIONAL CONFERENCE ON CYBERWORLDS (CW 2010) 331 - 337 2010 [Refereed][Not invited]
     
    Interactive rendering under complex real world illumination is essential for many applications such as material design, lighting design, and virtual realities. For such applications, interactive manipulations of viewpoints, lighting, BRDFs, and positions of objects are beneficial to designers and users. This paper proposes a system that acquires complex, all-frequency lighting environments and renders dynamic scenes under captured illumination, for lighting and material design applications in cyber worlds. To capture real world lighting environments easily, our method uses a camera equipped with a cellular phone. To handle dynamic scenes of rigid objects and dynamic BRDFs, our method decomposes the visibility function at each vertex of each object into the occlusion due to the object itself and occlusions due to other objects, which are represented by a nonlinear piecewise constant approximation, called cuts. Our method proposes a compact cut representation and efficient algorithm for cut operations. By using our system, interactive manipulation of positions of objects and realtime rendering with dynamic viewpoints, lighting, and BRDFs can be achieved.
  • K. Iwasaki, H. Uchida, Y. Dobashi, T. Nishita
    COMPUTER GRAPHICS FORUM 29 (7) 2215 - 2223 0167-7055 2010 [Refereed][Not invited]
     
    The visual simulation of natural phenomena has been widely studied. Although several methods have been proposed to simulate melting, the flows of meltwater drops on the surfaces of objects are not taken into account. In this paper, we propose a particle-based method for the simulation of the melting and freezing of ice objects and the interactions between ice and fluids. To simulate the flow of meltwater on ice and the formation of water droplets, a simple interfacial tension is proposed, which can be easily incorporated into common particle-based simulation methods such as Smoothed Particle Hydrodynamics. The computations of heat transfer, the phase transition between ice and water, the interactions between ice and fluids, and the separation of ice due to melting are further accelerated by implementing our method using CUDA. We demonstrate our simulation and rendering method for depicting melting ice at interactive frame-rates.
  • KUSUMOTO Katsutoshi, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi
    The IEICE transactions on information and systems (Japanese edetion) 一般社団法人電子情報通信学会 92 (12) 2270 - 2277 1880-4535 2009/12/01 [Not refereed][Not invited]
     
    三次元コンピュータグラフィックス(CG)の分野において,炎,煙,水などの流体現象のビジュアルシミュレーションは重要な研究テーマの一つである.また,従来の流体現象に関する研究を応用し,ユーザが所望する形状となるよう流体現象をコントロールする研究も興味深い研究テーマとして注目されている.本論文では,自然現象の中でも雲の表現に着目し,セル状に現れる雲のコントロール方法の提案を目的とする.セル状の雲をシミュレーションする際,その形状や大きさはシミュレーションに使用する様々なパラメータに依存してしまう.そのため,ユーザが意図した雲が生成されるようこれらのパラメータを手動で調節することは極めて難しい.そこで本研究では,ユーザが指定した分布の雲が自動生成されるよう流体シミュレーションをコントロールすることでこの問題点の改善を図る.
  • Controlling Explosion Simulation
    Yoshinori Dobashi, Shuhei Sato, Tsuyoshi Yamamoto, Ken Anjyo
    SIGGRAPH ASIA 2009 sketches 2009/12 [Refereed][Not invited]
  • Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita
    COMPUTER GRAPHICS FORUM 28 (7) 1935 - 1944 0167-7055 2009/10 [Refereed][Not invited]
     
    A rendering system for interior scenes is proposed in this paper The light reaches the interior scene, usually through small regions, such as windows or abat-jours, which we call portals. To provide a solution, suitable for rendering interior scenes with portals, we extend the traditional precomputed radiance transfer approaches. In our approach, a bounding sphere, which we call a shell, of the interior centered at each portal, is created and the light transferred from the shell towards the interior through the portal is precomputed. Each shell acts as an environment light source and its intensity distribution is determined by, rendering images of the scene, viewed from the center of the shell. By updating the intensity, distribution of the shell at each frame, we are able to handle dynamic objects outside the shells. The material of the portals can also be modified at run time (e.g. changing front transparent glass to frosted glass). Several applications are shown, including the illumination of a cathedral, lit by skylight at different times of a day, and a car, running in a town, at interactive frame rates, with a dynamic viewpoint.
  • Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    IPSJ Journal 一般社団法人情報処理学会 50 (8) 1917 - 1925 0387-5806 2009/08/15 [Not refereed][Not invited]
     
    This paper presents a BRDF modeling method, based on an inverse problem approach. Our method calculates BRDFs to match the appearance of the object specified by the user. By representing BRDFs by a linear combination of basis functions, outgoing radiances of the object surface can be represented using basis functions. The calculation of the desired BRDF results from calculating the corresponding coefficients of basis functions that minimize the sum of differences between the outgoing radiances, represented using basis functions and user specified radiances. The properties that BRDFs must sa...
  • Mikio Shinya, Michio Shiraishi, Yoshinori Dobashi, Kei Iwasaki, Tomoyuki Nishita
    IPSJ Journal 一般社団法人情報処理学会 50 (6) 1668 - 1678 0387-5806 2009/06/15 [Not refereed][Not invited]
     
    Lighting simulation is very important in realistic image synthesis, and the simulation of subsurface scattering has recently attracted much attention. Although the dipole/multipole model has succeeded in creating realistic images, it is still difficult to deal with volumetric features in subsurface scattering, which is important when rendering optically thin objects. This paper proposes a novel rendering method that utilizes the plane-parallel solution and the ray-marching method. The ray-marching method has been used to calculate single scattering solutions, and the plane-parallel solution...
  • Katsutoshi Kusumoto, Yoshinori Dobashi, Tsuyoshi Yamamoto
    Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers 一般社団法人映像情報メディア学会 63 (3) 355 - 360 1342-6907 2009/03 [Not refereed][Not invited]
     
    Displaying clouds is one of the important factors in creating images of outdoor scenes by using computer graphics. Methods based on fluid simulations are often used since they can simulate realistic cloud movements and shapes. However, although this approach can create realistic clouds, the resulting shapes and motion depend on many simulation parameters and their initial status. Therefore, it is very difficult to create the clouds of desired shapes. In this paper, we propose a method for generating clouds with shapes that users have specified. The user specifies the multiple shapes of the clouds at several key frames. Then our method automatically adjusts parameters during the simulation in order to generate clouds forming the specified shapes. Using the proposed method, clouds that change into specified shapes can be animated.
  • KOBAYASHI Toshiyasu, DOBASHI Yoshinori, YAMAOTO Tsuyoshi
    The IEICE transactions on information and systems (Japanese edetion) 一般社団法人電子情報通信学会 92 (2) 247 - 254 1880-4535 2009/02/01 [Not refereed][Not invited]
     
    コンピュータグラフィックス(CG)の分野において物理シミュレーションに基づく水や煙,炎などの流体現象の可視化に注目が集まっている.このような流体を表現するため,シミュレーション空間に格子を発生させて数値流体解析が行われる.しかし,移動物体を含む流体のシミュレーションにおいては,移動物体と流体との相互作用を表現するには膨大な計算コストを要する.このような問題を解消する手法として,重なり格子を用いた流体解析手法が提案されている.これはシミュレーション空間全体を覆う全体格子と物体周囲を覆う局所格子という複数の重なり合う格子を用いて情報交換しながら流体解析することで効率的に計算を行う手法である.本研究では,流体の一つである水に着目し,移動物体を含むシミュレーションにおいて重なり格子法を適用することで効率良く計算を行う手法を提案する.
  • Mikio Shinyat, Michio Shiraish, Yoshinori Dobashi, Kei Iwasaki, Tomoyuki Nishita
    Journal of the Institute of Image Electronics Engineers of Japan 画像電子学会 38 (4) 423 - 431 1348-0316 2009 [Not refereed][Not invited]
     
    Rendering scattering materials is an important issue in realistic rendering. This paper describes calculation and interpolation methods of BRDFs/BTDFs (Bidirectional Reflectance/Transmittance Distribution Functions) of scattering materials. We introduced the plane-parallel scattering theory, which enables us analytic calculation of BRDFs/BTDFs of uniform scattering materials. We analysed calculated BRDFs/BTDFs and proposed their interpolation methods against scattering parameters and width of scattering materials. © 2009, The Institute of Image Electronics Engineers of Japan. All rights reserved.
  • Shinya Mikio, Shiraishi Michio, Dobashi Yoshinori, Iwasaki Kei, Nishita Tomoyuki
    Information and Media Technologies Information and Media Technologies 編集運営会議 4 (3) 655 - 665 2009 
    Lighting simulation is very important in realistic image synthesis, and the simulation of subsurface scattering has recently attracted much attention. Although the dipole/multipole model has succeeded in creating realistic images, it is still difficult to deal with volumetric features in subsurface scattering, which is important when rendering optically thin objects. This paper proposes a novel rendering method that utilizes the plane-parallel solution and the ray-marching method. The ray-marching method has been used to calculate single scattering solutions, and the plane-parallel solution has been adopted to calculate BRDFs. By combining these techniques, the proposed method efficiently captures volumetric features in multiple subsurface scattering events. In our experiments, the proposed method demonstrated a performance superior to that of previous methods in terms of accuracy.
  • Siren Bato, Yoshinori Dobashi, Tsuyoshi Yamamoto
    2nd International Workshop on Computer Science and Engineering, WCSE 2009 1 288 - 292 2009 [Refereed][Not invited]
     
    This paper proposes a new, simple and effective image based rendering (IBR) technique for rendering new viewpoint images from large unstructured image set. Unlike most of the existing image based rendering systems, the proposed system is compatible with the standard model based rendering systems and able to synthesize the target scene with other artificial CG objects or scenes. © 2009 IEEE.
  • Siren Bato, Yoshinori Dobashi, Tsuyoshi Yamamoto
    Proceedings of the IADIS International Conference Applied Computing 2009, 19-21 November, Rome, Italy, 2 Volumes IADIS Press 369 - 386 2009 [Refereed][Not invited]
  • Kei Iwasaki, Yoshinori Dobashi, Fujiichi Yoshimoto, Tomoyuki Nishita
    GRAPP 2009: PROCEEDINGS OF THE FOURTH INTERNATIONAL CONFERENCE ON COMPUTER GRAPHICS THEORY AND APPLICATIONS 129 - + 2009 [Refereed][Not invited]
     
    This paper presents a BRDF modeling method, based on an inverse problem approach. Our method calculates BRDFs to match the appearance of the object specified by the user. By representing BRDFs by a linear combination of basis functions, outgoing radiances of the object surface can be represented using basis functions. The calculation of the desired BRDF results from calculating the corresponding coefficients of basis functions that minimize the sum of differences between the outgoing radiances, represented using basis functions and user specified radiances. The properties that BRDFs must satisfy are described by linear constraint conditions. This minimization problem can be solved, interactively, using a linearly constrained least squares approach. Thus, our method allows the user to design BRDFs directly, under fixed complex lighting and viewpoint, and to view the rendering results interactively, under dynamic lighting and viewpoint.
  • Yoshinori Dobashi
    2009 11TH IEEE INTERNATIONAL CONFERENCE ON COMPUTER-AIDED DESIGN AND COMPUTER GRAPHICS, PROCEEDINGS 30 - 31 2009 [Refereed][Not invited]
     
    Visual simulation of natural phenomena has become one of the most important research topics in computer graphics. Such phenomena include water, fire, smoke, clouds, and so on. Recent methods for the simulation of these phenomena utilize techniques developed in computational fluid dynamics. In this paper, the basic equations (Navier-Stokes equations) for simulating these phenomena are briefly described. These basic equations are used to simulate various natural phenomena. This paper then explains our applications of the equations for simulations of smoke, clouds, and aerodynamic sound.
  • Mikio Shinya, Michio Shiraishi, Yoshinori Dobashi, Kei Iwasaki, Tomoyuki Nishita
    Journal of Information Processing 17 180 - 190 1882-6652 2009 [Refereed][Not invited]
     
    Lighting simulation is very important in realistic image synthesis, and the simulation of subsurface scattering has recently attracted much attention. Although the dipole/multipole model has succeeded in creating realistic images, it is still difficult to deal with volumetric features in subsurface scattering, which is important when rendering optically thin objects. This paper proposes a novel rendering method that utilizes the plane-parallel solution and the ray-marching method. The ray-marching method has been used to calculate single scattering solutions, and the plane-parallel solution has been adopted to calculate BRDFs. By combining these techniques, the proposed method efficiently captures volumetric features in multiple subsurface scattering events. In our experiments, the proposed method demonstrated a performance superior to that of previous methods in terms of accuracy.
  • Yoshinori Dobashi, Katsutoshi Kusumoto, Tomoyuki Nishita, Tsuyoshi Yamamoto
    ACM TRANSACTIONS ON GRAPHICS 27 (3) Article 94  0730-0301 2008/08 [Refereed][Not invited]
     
    Clouds play an important role for creating realistic images of outdoor scenes. In order to generate realistic clouds, many methods have been developed for modeling and animating clouds. One of the most effective approaches for synthesizing realistic clouds is to simulate cloud formation processes based on the atmospheric fluid dynamics. Although this approach can create realistic clouds, the resulting shapes and motion depend on many simulation parameters and the initial status. Therefore, it is very difficult to adjust those parameters so that the clouds form the desired shapes. This paper addresses this problem and presents a method for controlling the simulation of cloud formation. In this paper, we focus on controlling cumuliform cloud formation. The user specifies the overall shape of the clouds. Then, our method automatically adjusts parameters during the simulation in order to generate clouds forming the specified shape. Our method can generate realistic clouds while their shapes closely match to the desired shape.
  • Yoshinori Dobashi, Yasuhiro Matsuda, Tsuyoshi Yamamoto, Tomoyuki Nishita
    COMPUTER GRAPHICS FORUM 27 (2) 477 - 486 0167-7055 2008/04 [Refereed][Not invited]
     
    Recently, many techniques using computational fluid dynamics have been proposed for the simulation of natural phenomena such as smoke and fire. Traditionally, a single grid is used for computing the motion of fluids. When an object interacts with a fluid, the resolution of the grid must be sufficiently high because the shape of the object is represented by a shape sampled at the grid points. This increases the number of grid points that are required, and hence the computational cost is increased. To address this problem, we propose a method using multiple grids that overlap with each other. In addition to a large single grid (a global grid) that covers the whole of the simulation space, separate grids (local grids) are generated that surround each object. The resolution of a local grid is higher than that of the global grid. The local grids move according to the motion of the objects. Therefore, the process of resampling the shape of the object is unnecessary when the object moves. To accelerate the computation, appropriate resolutions are adaptively-determined for the local grids according to their distance from the viewpoint. Furthermore, since we use regular (orthogonal) lattices for the grids, the method is suitable for GPU implementation. This realizes the real-time simulation of interactions between objects and smoke.
  • Kei Iwasaki, Yoshinori Dobashi, Fujiichi Yoshimoto, Tomoyuki Nishita
    VISUAL COMPUTER 24 (2) 77 - 84 0178-2789 2008/02 [Refereed][Not invited]
     
    Particle-based simulations are widely used to simulate fluids. We present a real-time rendering method for the results of particle-based simulations of water. Traditional approaches to visualize the results of particle-based simulations construct water surfaces that are usually represented by polygons. To construct water surfaces from the results of particle-based simulations, a density function is assigned to each particle and a density field is computed by accumulating the values of the density functions of all particles. However, the computation of the density field is time consuming. To address this problem, we propose an efficient calculation of density field using a graphics processing unit (GPU). We present a rendering method for water surfaces sampled by points. The use of the GPU permits efficient simulation of optical effects, such as refraction, reflection, and caustics.
  • IIZUKA Taro, Yonghao Yue, DOBASHI Yoshinori, NIHSITA Tomoyuki
    ITE Technical Report 一般社団法人 映像情報メディア学会 32 99 - 104 2008 
    From the psychological point of view, it is said that people feel comfortable if the rhythms of sound and video are synchronized. Therefore, works for the synchronization are performed frequently in the process of content making. We are aimed at developing a computer assisted system for the synchronization, which was done manually. In our system, we detect rapid variations in the sound and the video as accents, and adjust the playback speed of the video to make the accents of the video and the sound matched. To detect the accents, we first calculate the time-varying local variances of the variation in the signals, and determine the local thresholds for the detection. Next, we extract signals which exceed the thresholds as accents and assign the exceeded amount as the weight of each accent. In the synchronization process, we first take into account both the weights and the time difference between the occurrences of the accents of the sound and the video, and search a best matched accent of the video for each accent of the sound. Then, we adjust the playback speed of the video to ensure that the difference between the occurrences of the pair of the accents is small enough that people would not feel uncomfortable.
  • Yoshinori Dobashi, Tsuyoshi Yamamoto, Tomoyuki Nishtia
    SIGGRAPH'08: ACM SIGGRAPH Talks 2008 2008 [Refereed][Not invited]
  • Yoshinori Dobashi, Katsutoshi Kusumoto, Tomoyuki Nishita, Tsuyoshi Yamamoto
    ACM Trans. Graph. 27 (3) 2008 [Refereed][Not invited]
  • Yoshinori Dobashi, Yoshihiro Enjyo, Tsuyoshi Yamamoto, Tomoyuki Nishita
    VISUAL COMPUTER 23 (9-11) 697 - 705 0178-2789 2007/09 [Refereed][Not invited]
     
    Methods for rendering natural scenes are used in many applications such as virtual reality, computer games, and flight simulators. In this paper, we focus on the rendering of outdoor scenes that include clouds and lightning. In such scenes, the intensity at a point in the clouds has to be calculated by taking into account the illumination due to lightning. The multiple scattering of light inside clouds is an important factor when creating realistic images. However, the computation of multiple scattering is very time-consuming. To address this problem, this paper proposes a fast method for rendering clouds that are illuminated by lightning. The proposed method consists of two processes. First, basis intensities are prepared in a preprocess step. The basis intensities are the intensities at points in the clouds that are illuminated by a set of point light sources. In this precomputation, both the direct light and also indirect light (i.e., multiple scattering) are taken into account. In the rendering process, the intensities of clouds are calculated in real-time by using the weighted sum of the basis intensities. A further increase in speed is achieved by using a wavelet transformation. Our method achieves the real-time rendering of realistic clouds illuminated by lightning.
  • Yoshinori Dobashi, Tsuyoshi Yamamoto, Makoto Sato, Shoichi Hasegawa, Mitsuaki Kato, Tomoyuki Nishita
    IEEE COMPUTER GRAPHICS AND APPLICATIONS 27 (3) 90 - 92 0272-1716 2007/05 [Refereed][Not invited]
  • Sakai Masahiro, Ichijo Noriyuki, Dobashi Yoshinori, Yamamoto Tsuyoshi
    The journal of the Institute of Image Information and Television Engineers 一般社団法人映像情報メディア学会 61 (4) 488 - 494 1342-6907 2007/04/01 [Not refereed][Not invited]
     
    Web3D techniques for managing 3DCG in the contents of HTML pages have made remarkable progress since VRML appeared in 1995. Many Web3D systems use fixed shaders for graphics API for realtime 3DCG rendering, so it is difficult to simulate the global illumination. We propose a solution to the problem of global illumination that uses a Web3D environment map in our proprietary Web3D format, '3DX' and the GPU shading language.
  • Enjyo Yoshihiro, Dobashi Yoshinori, Yamamoto Tsuyoshi
    The journal of the Institute of Image Information and Television Engineers 一般社団法人映像情報メディア学会 61 (4) 482 - 487 1342-6907 2007/04/01 [Not refereed][Not invited]
     
    Recently, simulating natural phenomena has become one of the most important research areas in computer graphics. We focus on the visual simulation of fire. First, we propose an interactive method to simulate the motion of fire. Our method allows the user to control the shape and motion of fire. This is achieved by combining cellular automata and particle systems. Secondly, we propose a fast rendering method using wavelets for surrounding objects illuminated by the fire. The method can take into account not only direct light but also indirect light. This method achieves fast calculation of d...
  • Yoshitaka Moro, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers 一般社団法人映像情報メディア学会 61 (10) 1457 - 1462 1342-6907 2007 [Not refereed][Not invited]
     
    Physically based fluid simulation is one of the most important research topics in computer graphics. Although many methods have been developed that use 3D or 2D grids to simulate fluids, there are few methodd for simulating fluid flows on surfaces. We present a real-time particle-based simulation method for the flows on surfaces. The surfaces are parameterized in a 2D parameter domain and physical quantities of particles are calculated in the parameter domain. The flows are simulated by updating the physical quantities of the particles, and the simulation is accelerated with a GPU. Our method simulates the fluid flows of 30,000 particles in real-time.
  • Yonghao Yue, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    ACM SIGGRAPH 2007 Sketches, SIGGRAPH'07 2007 [Refereed][Not invited]
  • Kei Iwasaki, Yoshinori Dobashi, Fujiichi Yoshimoto, Tomoyuki Nishita
    Proceedings of the Eurographics Symposium on Rendering Techniques, Grenoble, France, 2007 Eurographics Association 35 - 44 2007 [Refereed][Not invited]
  • Yonghao Yue, Kei Iwasaki, Yoshinori Dobashi, Tornoyuki Nishita
    PACIFIC GRAPHICS 2007: 15TH PACIFIC CONFERENCE ON COMPUTER GRAPHICS AND APPLICATIONS 87 - + 2007 [Refereed][Not invited]
     
    In this paper we propose a fast global illumination solution for interactive lighting design. Using our method, light sources and the viewpoint are movable, and the characteristics of materials can be modified (assuming low-frequency BRDF) during rendering. Our solution is based on particle tracing (a variation of photon mapping) and final gathering. We assume that objects in the input scene are static, and pre-compute potential light paths for particle tracing and final gathering. To perfom final gathering fast, we propose an efficient technique called Hierarchical Histogram Estimation for rapid estimation of radiances from the distribution of the particles. The rendering process of our method can be fully implemented on the GPU and our method achieves interactive frame rates for rendering scenes with even more than 100, 000 triangles.
  • Kei Iwasaki, Yoshinori Dobashi, Naoki Tamura, Henry Johan, Fujiichi Yoshimoto, Tomoyuki Nishita
    ACM SIGGRAPH 2006: Sketches, SIGGRAPH '06 2006 [Refereed][Not invited]
  • Yoshinori Dobashi, Makoto Sato, Shoichi Hasegawa, Tsuyoshi Yamamoto, Mitsuaki Kato, Tomoyuki Nishita
    Proceedings of the ACM Symposium on Virtual Reality Software and Technology, VRST 91 - 99 2006 [Refereed][Not invited]
     
    Haptic interfaces enable us to interact with a virtual world using our sense of touch. This paper presents a method for realizing haptic interaction with water. Our method displays forces acting on rigid objects due to water with a high frame rate (500 Hz). To achieve this, we present a fast method for simulating the dynamics of water. We decompose the dynamics into two parts. One is a linear flow expressed by a wave equation used to compute water waves. The other is a more complex and non-linear flow around the object. The fluid forces due to the non-linear flow is precomputed by solving Navier-Stokes equations, and stored in a database, named the Fluid Resistance Map. The precomputed non-linear flow and the linear flow are combined to compute the forces due to water. Copyright 2006 ACM.
  • Kei Iwasaki, Yoshinori Dobashi, Fujiichi Yoshimotol, Tomoyuki Nishita
    ADVANCES IN COMPUTER GRAPHICS, PROCEEDINGS 4035 102 - 114 0302-9743 2006 [Refereed][Not invited]
     
    In recent years, attention has been paid to particle-based fluid simulation, with several methods being developed to incorporate particle-based simulation into CG animations. These methods reconstruct water surfaces that are usually represented by polygons. However, the computational cost of the surface reconstruction is quite high. Therefore, it is difficult to render the result of the particle-based simulation at interactive frame rates. To address this, we present a real-time method for rendering water surfaces resulting from particle-based simulation. We present an efficient GPU accelerated surface reconstruction method from particles, sampling the water surface point by point. In addition to rendering the point based water surfaces, the use of the GPU permits efficient simulation of optical effects such as refraction, reflection, and caustics.
  • Shoichi Hasegawa, Makoto Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto, Mitsuaki Kato, Tomoyuki Nishita
    ACM SIGGRAPH 2005 Emerging Technologies, SIGGRAPH 2005 28  2005/07/31 [Refereed][Not invited]
  • K Iwasaki, F Yoshimoto, Y Dobashi, T Nishita
    IEICE TRANSACTIONS ON INFORMATION AND SYSTEMS E88D (5) 904 - 911 1745-1361 2005/05 [Refereed][Not invited]
     
    Caustics are patterns of light focused by reflective or refractive objects. Because of their visually fascinating patterns, several methods have been developed to render caustics. We propose a method for the quick rendering of caustics formed by refracted and converged light through transparent objects. First, in the preprocess, we calculate sampling rays incident on each vertex of the object, and trace the rays until they leave the object taking refraction into account. The position and direction of each ray that finally transmits the transparent object are obtained and stored in a lookup table. Next, in the rendering process, when the object is illuminated, the positions and directions of the rays leaving the object are calculated using the lookup table. This makes it possible to render refractive caustics due to transparent objects at interactive frame rates, allowing us to change the light position and direction, and translate and rotate the object.
  • JOHAN Henry, MATSUI Hajime, HAGA Toshiyuki, DOBASHI Yoshinori, NISHITA Tomoyuki
    The transactions of the Institute of Electronics, Information and Communication Engineers. D-II 一般社団法人電子情報通信学会 88 (2) 358 - 367 0915-1923 2005/02/01 [Not refereed][Not invited]
     
    本論文は入力された画像に対して様々なアート風画像を生成するノンフォトリアリスティクレンダリング手法を提案する.アート風画像には, モザイクやステンドグラスなどの領域分割ベースのものや油絵などのストロークベースのものがあるが, 提案法はその両方を生成することを可能にするものである.アート風画像においては, エッジ(色の境界)が強調されることや, 色変化の少ない部分が同じ色で描かれることが一般的である.そこで提案法では, まず入力画像をいくつかの領域の集合として近似する.この領域分割は, 領域の境界ができるだけ入力画像のエッジと一致するようにして, 各領域は1色で塗りつぶすというのであり, ボロノイ図を利用して実現される.続いて, ボロノイ領域をそのまま利用すれば領域分割ベースの画像, 色の近い隣接領域をたどるように筆のストロークを描けばストロークベースの画像を生成することができる.
  • Junji Suzuki, Tomoya Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto
    Journal of the Institute of Image Electronics Engineers of Japan 画像電子学会 34 (4) 302 - 310 1348-0316 2005 [Not refereed][Not invited]
     
    Recently, many researchers have paid attention to a technique called non-photorealistic rendering (NPR). In this paper, we propose a method for painterly rendering of water surface. The painterly images of water surface are efficiently generated by making use of techniques used in the field of three-dimensional computer graphics. Our method can create not only static images but also painterly animations of water such as a river. Moreover, we develop an interactive system using our method. This enables the user to reflect the user's mind on the resulting images. © 2005, The Institute of Image Electronics Engineers of Japan. All rights reserved.
  • Kei Iwasaki, Fujiichi Yoshimoto, Yoshinori Dobashi, Tomoyuki Nishita
    IEICE Transactions on Information and Systems E88-D (5) 904 - 910 0916-8532 2005 [Refereed][Not invited]
     
    Caustics are patterns of light focused by reflective or refractive objects. Because of their visually fascinating patterns, several methods have been developed to render caustics. We propose a method for the quick rendering of caustics formed by refracted and converged light through transparent objects. First, in the preprocess, we calculate sampling rays incident on each vertex of the object, and trace the rays until they leave the object taking refraction into account. The position and direction of each ray that finally transmits the transparent object are obtained and stored in a lookup table. Next, in the rendering process, when the object is illuminated, the positions and directions of the rays leaving the object are calculated using the lookup table. This makes it possible to render refractive caustics due to transparent objects at interactive frame rates, allowing us to change the light position and direction, and translate and rotate the object. Copyright © 2005 The Institute of Electronics, Information and Communication Engineers.
  • MIYAZAKI Ryo, DOBASHI Yoshinori, NISHITA Tomoyuki
    The transactions of the Institute of Electronics, Information and Communication Engineers. D-II 一般社団法人電子情報通信学会 87 (9) 1814 - 1822 0915-1923 2004/09/01 [Not refereed][Not invited]
     
    雲,煙,炎,水などの自然現象のシミュレーションはCGにおいて重要な研究分野の一つであり,特に雲の表示は景観画像の作成に重要な役割を果たす.リアルな雲を表現するためには,計算コストはかかるが流体シミュレーションに基づく手法が有効である.本論文では大気流体のモデルの差分法による数値解法を用い,積雲のリアルなアニメーションを作成することを目的とする.また障害物として山を考慮することにより,従来法では取り扱われていなかった気流と山との衝突により生成される雲のシミュレーションも行う.しかし差分法は通常,空間をグリッドに分割して行うが,リアルな雲を作成するためには空間を細かいグリッドに分割することが必要になり,それに伴い計算コストは増大してしまう.そこでグリッドをアダプティブに分割・統合していくアダプティブグリッド法を導入する.用いる総グリッド数を大幅に抑えることができ,効率的なシミュレーションを行うことができる.そしてシミュレーションで得られた雲の密度分布をレンダリングしてリアルなアニメーションを作成する.
  • R Mizuno, Y Dobashi, T Nishita
    JOURNAL OF INFORMATION SCIENCE AND ENGINEERING 20 (2) 219 - 232 1016-2364 2004/03 [Refereed][Not invited]
     
    In this paper, the model of volcanic clouds for computer graphics using the Coupled Map Lattice (CML) method is proposed. In this model, the Navier-Stokes equations are used, and the equations are solved by using the CML method that can be applied as an efficient fluid solver. Moreover, to generate desired shape of volcanic clouds, some parameters that allow intuitively control of the shape are provided. Hence, in this system, the behavior of the volcanic clouds can be calculated in practical calculation time, and by only changing some parameters various shapes of the volcanic clouds can be generated. Therefore, photo-realistic images/animations of various shapes of volcanic clouds can be created efficiently by the proposed approach.
  • Yoshinori Dobashi, Tsuyoshi Yamamoto, Tomoyuki Nishita
    Computer Graphics Forum 23 (3) 539 - 545 0167-7055 2004 [Refereed][Not invited]
     
    Sound is an indispensable element for the simulation of a realistic virtual environment. Therefore, there has been much recent research focused on the simulation of realistic sound effects. This paper proposes a method for creating sound for turbulent phenomena such as fire. In a turbulent field, the complex motion of vortices leads to the generation of sound. This type of sound is called a vortex sound. The proposed method simulates a vortex sound by computing vorticity distributions using computational fluid dynamics. Sound textures for the vortex sound are first created in a pre-process step. The sound is then created at interactive rates by using these sound textures. The usefulness of the proposed method is demonstrated by applying it to the simulation of the sound of fire and other turbulent phenomena.
  • Kei Iwasaki, Tetsuichi Yanagita, Tomoyuki Nishita, Yoshinori Dobashi
    Journal of the Institute of Image Electronics Engineers of Japan 画像電子学会 33 (3) 515 - 522 1348-0316 2004 [Not refereed][Not invited]
     
    The sky color is indispensable for the display of natural scenes in computer graphics. To render the photorealistic images of the sky, the calculation taking into account multiple scattering is necessary. However the calculation is so complex that enormous computational cost is required. Therefore, in this paper, we proposed a method using virtual shells (sampling shells) generated in the atmosphere. In the method, the illumination distribution of the scattering of light on the virtual shells is considered as a texture map called scattering maps. This makes it possible to calculate the sky color effeciently by using graphics hardware. Furthermore, we also propose a calculation and rendering method using the singular value decomposition to display the sky quickly with a little memory when the height of the viewpoint and the sun altitude change. © 2004, The Institute of Image Electronics Engineers of Japan. All rights reserved.
  • Tomoya Sato, Yoshinori Dobashi, Tsuyoahi Yamamoto, Katsumi Takao, Ken Anjyo
    Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers 一般社団法人映像情報メディア学会 58 (10) 1483 - 1488 1342-6907 2004 [Not refereed][Not invited]
     
    In a cel animation workplace, non-photorealistic rendering (NPR) techniques are often applied to a 3D scene model, which is constructed by referring to the 2D hand-drawn images of the scene. There exist a lot of scene features that must be modeled from the 2D information. The accentuation effects are amongst the most important features in a hand-drawn scene. In this context, accentuation refers to adding hand-drawn shading of the scene. The specific region that an artist wishes the viewer to observe is drawn more brightly than the other regions. We propose a method of extracting the accentuation effects from a single 2D painted image of an animated scene. This method enables the automatic addition of the accentuation effects to each frame of the animation, observed from other viewpoints.
  • R Miyazaki, Y Dobashi, T Nishita
    Proceedings of the Seventh IASTED International Conference on Computer Graphics and Imaging 93 - 98 2004 [Refereed][Not invited]
     
    Clouds make an important contribution when composing images for various applications such as virtual outdoor scenes. An efficient rendering method is proposed for the rendering of clouds suitable for graphics hardware. Most of the calculations for rendering clouds are processed by texture operations in the graphics hardware. The method creates images of clouds processing photo realism by taking into account the single scattering of light, shadows on the ground, and shafts of light through the clouds. It is necessary to consider the light attenuation in the sun direction and in the view direction to render the volume data of the cloud density. These attenuations are calculated in a single step, using a sectional technique called "shadow-view slice".
  • Y Dobashi, T Yamamoto, T Nishita
    12TH PACIFIC CONFERENCE ON COMPUTER GRAPHICS AND APPLICATIONS, PROCEEDINGS 152 - 159 2004 [Refereed][Not invited]
     
    In this paper, we propose a radiosity method for the point-sampled geometry to compute diffuse interreflection of light. Most traditional radiosity methods subdivide the surfaces of objects into small elements such as quadrilaterals. However the point-sampled geometry includes no explicit information about surfaces, presenting a difficulty in applying the traditional approach to the point-sampled geometry. The proposed method addresses this problem by computing the interreflection without reconstructing any surfaces. The method realizes lighting simulations without losing the advantages of the point-sampled geometry.
  • K Iwasaki, F Yoshimoto, Y Dobashi, T Nishita
    2004 INTERNATIONAL CONFERENCE ON CYBERWORLDS, PROCEEDINGS 39 - 44 2004 [Refereed][Not invited]
     
    Caustics are patterns of light formed by reflection or refraction of light from objects, and several methods have been developed to render caustics because of their visually beautiful patterns. This paper proposes a method for the rapid rendering of caustics formed by refracted light through transparent objects. First, a preprocess is used to generate sampling rays incident on each vertex of the object, and, taking refraction into account, to trace the rays until they leave the object. The position and direction of each ray that finally leaves the transparent object are obtained and stored in a lookup table. Next, in the rendering process, when the object is illuminated, the position and direction of the rays leaving the object are calculated using the lookup table. This makes it possible to render refractive caustics due to transparent objects at interactive frame rates even if the direction of the light changes and the object is translated or rotated.
  • T Sato, Y Dobashi, T Yamamoto, K Takao, K Anjyo
    COMPUTER GRAPHICS INTERNATIONAL, PROCEEDINGS 222 - 229 2004 [Refereed][Not invited]
     
    In a cel animation workplace, non-photorealistic rendering techniques are often applied to a 3D scene model, which is constructed by referring to the 2D hand-drawn images of the scene. There exist a lot of scene features that must be modeled from the 2D information. The accentuation effects are amongst the most important features in a hand-drawn scene. In this context, accentuation refers to adding hand-drawn shading of the scene. The specific region that an artist wishes the viewer to observe is drawn brighter than the other regions. In this paper, a method is proposed for the extraction of the accentuation effects from a single 2D painted image of an animated scene. This method enables the automatic addition of the accentuation effects to each frame of the animation, observed from other viewpoints.
  • Y Dobashi, T Yamamoto, T Nishita
    COMPUTER GRAPHICS FORUM 23 (3) 539 - 545 0167-7055 2004 [Refereed][Not invited]
     
    Sound is an indispensable element for the simulation of a realistic virtual environment. Therefore, there has been much recent research focused on the simulation of realistic sound effects. This paper proposes a method for creating sound for turbulent phenomena such as fire. In a turbulent field, the complex motion of vortices leads to the generation of sound. This type of sound is called a vortex sound. The proposed method simulates a vortex sound by computing vorticity distributions using computational fluid dynamics. Sound textures for the vortex sound are first created in a pre-process step. The sound is then created at interactive rates by using these sound textures. The usefulness of the proposed method is demonstrated by applying it to the simulation of the sound of fire and other turbulent phenomena.
  • K. Iwasaki, Y.Dobashi, T.Nishita
    Computer Graphics Forum 23 (3) 601 - 609 2003/11 [Refereed][Not invited]
  • Yoshinori Dobashi, Tsuyoshi Yamamoto, Tomoyuki Nishita
    ACM Transactions on Graphics 22 (3) 732 - 740 0730-0301 2003/07 [Refereed][Not invited]
     
    In computer graphics, most research focuses on creating images, However, there has been much recent work on the automatic generation of sound linked to objects in motion and the relative positions of receivers and sound sources. This paper proposes a new method for creating one type of sound called aerodynamic sound. Examples of aerodynamic sound include sound generated by swinging swords or by wind blowing. A major source of aerodynamic sound is vortices generated in fluids such as air. First, we propose a method for creating sound textures for aerodynamic sound by making use of computational fluid dynamics. Next, we propose a method using the sound textures for real-time rendering of aerodynamic sound according to the motion of objects or wind velocity. © 2003 ACM.
  • Y Dobashi, T Yamamoto, T Nishita
    ACM TRANSACTIONS ON GRAPHICS 22 (3) 732 - 740 0730-0301 2003/07 [Refereed][Not invited]
     
    In computer graphics, most research focuses on creating images. However, there has been much recent work on the automatic generation of sound linked to objects in motion and the relative positions of receivers and sound sources. This paper proposes a new method for creating one type of sound called aerodynamic sound. Examples of aerodynamic sound include sound generated by swinging swords or by wind blowing. A major source of aerodynamic sound is vortices generated in fluids such as air. First, we propose a method for creating sound textures for aerodynamic sound by making use of computational fluid dynamics. Next, we propose a method using the sound textures for real-time rendering of aerodynamic sound according to the motion of objects or wind velocity.
  • Tomoya Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto
    IFIP Advances in Information and Communication Technology 112 125 - 132 1868-4238 2003 [Refereed][Not invited]
     
    Many researchers have been studying computer graphics simulations of natural phenomena. One important area in these studies is the animation of water droplets, whose applications include drive simulators. Because of the complexity of shape and motion, the animation of water droplets requires long calculation time. This paper proposes a method for real-time animations of water droplets running down on a glass plate, using graphics hardware. The proposed method takes into account depth of field effects, and makes it possible to change the focal point interactively depending on a point in the center of the scene being observed. © 2003 by Springer Science+Business Media New York.
  • Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    ACM International Conference Proceeding Series 45 129 - 171 2003 [Refereed][Not invited]
     
    We present a fast volume rendering technique for sea surfaces taking into account second order scattering using graphics hardware. To generate realistic images of the sea surfaces, accurate simulation of light transport within water is necessary. In particular, multiple scattering due to particles in the water plays an important role in creating realistic images. In this paper, we introduce the concept of a scattering map for efficient computation of light scattering within water volume. In order to calculate second order scattering of light, we slice the water volume into virtual horizontal planes and calculate the radiance from second order scattering of light at sampling points on these planes. The radiance on the virtual planes can be treated as a texture map. This makes it possible to accelerate the computation using graphics hardware. © The Eurographics Association 2003.
  • R Mizuno, Y Dobashi, BY Chen, T Nishita
    11TH PACIFIC CONFERENCE ON COMPUTER GRAPHICS AND APPLICATIONS, PROCEEDINGS 440 - 444 2003 [Refereed][Not invited]
     
    In this paper, we present a physics motivated modeling method for volcanic clouds as a two fluids model. Some previous methods model smoke or clouds as one fluid, but the volcanic clouds can not be treated as one fluid. The volcanic clouds consist of the pyroclasts, the volcanic gas and the entrained air. Since the pyroclasts and the volcanic gas can be treated as one fluid, called magma, the volcanic clouds are regarded as two fluids, the magma and the entrained air. The modeling in the 3D analysis space can be simplified to enhance the performance. Since our approach is physics motivated, it can be used to generate physically reasonable and realistic images of volcanic clouds from the volcanic initial eruption to the equilibrium situation.
  • K Iwasaki, Y Dobashi, T Nishita
    COMPUTER GRAPHICS FORUM 22 (3) 601 - 609 0167-7055 2003 [Refereed][Not invited]
     
    In order to synthesize realistic images of scenes that include water surfaces, the rendering of optical affects caused by waves on the water surface, such as caustics and reflection, is necessary. However, rendering caustics is quite complex and time-consuming. In recent years, the performance of graphics hardware has made significant progress. This fact encourages researchers to study the acceleration of realistic image synthesis. We present here a method for the fast rendering of refractive and reflective caustics due to water surfaces. In the proposed method, an object is expressed by a set of texture mapped slices. We calculate the intensities of the caustics on the object by using the slices and store the intensities as textures. This makes it possible to render caustics at interactive rate by using graphics hardware. Moreover, we render objects that are reflected and refracted due to the water surface by using reflection/refraction mapping of these slices.
  • Development of Web-Based Training System and Courseware for Advanced Computer Graphics Courses Enhanced by Interactive JAVA Applets
    Tomoyuki Nishita, Kunio Kondo, Yoshio Ohno, Yoshiaki Takai, Kenjiro T.Miura, Yoshinori Dobashi, Tokiichiro Takahashi
    Proc. of the 10th Int. Conf. on Geometry and Graphics 2 123 - 128 2002/08 [Refereed][Not invited]
  • Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita
    Computer Graphics Forum 21 (4) 701 - 711 0167-7055 2002 [Refereed][Not invited]
     
    The display of realistic natural scenes is one of the most important research areas in computer graphics. The rendering of water is one of the essential components. This paper proposes an efficient method for rendering images of scenes within water. For underwater scenery, the shafts of light and caustics are attractive and important elements. However, computing these effects is difficult and time-consuming since light refracts when passing through waves. To address the problem, our method makes use of graphics hardware to accelerate the computation. Our method displays the shafts of light by accumulating the intensities of streaks of light by using hardware color blending functions. Making use of a Z-buffer and a stencil buffer accelerates the rendering of caustics. Moreover, by using a shadow mapping technique, our method can display shafts of light and caustics taking account of shadows due to objects.
  • Y Dobashi, T Yamamoto, T Nishita
    NINTH PACIFIC CONFERENCE ON COMPUTER GRAPHICS AND APPLICATIONS, PROCEEDINGS 390 - 399 2001 [Refereed][Not invited]
     
    A number of methods have been developed for creating realistic images of natural scenes. Their applications include flight simulators, the visual assessment of outdoor scenery, etc. Previously, many of these methods have focused on creating images under clear or slightly cloudy days. Simulations under bad weather conditions, however are one of the important issues for realism. Lightning is one of the essential elements for these types of simulations. This paper proposes an efficient method for creating realistic images of scenes including lightning. Our method can create photo-realistic images by taking into account the scattering effects due to clouds and atmospheric particles illuminated by lightning. Moreover graphics hardware is utilized to accelerate the image generation. The usefulness of our method is demonstrated by creating images of outdoor scenes that include lightning.
  • K Iwasaki, Y Dobashi, T Nishita
    NINTH PACIFIC CONFERENCE ON COMPUTER GRAPHICS AND APPLICATIONS, PROCEEDINGS 374 - 383 2001 [Refereed][Not invited]
     
    The display of realistic natural scenes is one of the most important research areas in computer graphics. The rendering of water is one of the essential components. This paper proposes an efficient method for rendering images of scenes within water For underwater scenery, the shafts of light and caustics are attractive and important elements. However computing these effects is difficult and time-consuming since light refracts when passing through waves. To address the problem, our method makes use of graphics hardware to accelerate the computation. Our method displays the shafts of light by accumulating the intensities of streaks of light by using hardware color blending functions. The rendering of caustics is accelerated by making use of a Z-buffer and a stencil buffer. Moreover, by using a shadow mapping technique, our method can display shafts of light and caustics taking account of shadows due to objects.
  • R Miyazaki, S Yoshida, Y Dobashi, T Nishita
    NINTH PACIFIC CONFERENCE ON COMPUTER GRAPHICS AND APPLICATIONS, PROCEEDINGS 363 - 372 2001 [Refereed][Not invited]
     
    The simulation of natural phenomena such as clouds, smoke, fire and water is one of the most important research areas in computer graphics. In particular, clouds play an important role in creating images of outdoor scenes. The proposed method is based on the physical simulation of atmospheric flu id dynamics which characterizes the shape of clouds. To take account of the dynamics, we used a method called the coupled map lattice (CML). CML is an extended method of cellular automaton and is computationally inexpensive. The proposed method can create various types of clouds and can also realize the animation of these clouds. Moreover, we have developed an interactive system for modeling various types of clouds.
  • T Nishita, Y Dobashi
    COMPUTER GRAPHICS INTERNATIONAL 2001, PROCEEDINGS 149 - 156 2001 [Refereed][Not invited]
     
    The simulation of various natural phenomena is one of the important research fields in computer graphics. In particular, aspects such as sky, clouds, water, fire, trees, smoke, terrains, desert scenes, snow and fog are indispensable for creating realistic images of natural scenes, fight simulators and so on. Therefore, a lot of researchers have been trying to develop methods for simulating and rendering these. In this paper, we focus Oil sky, clouds, smoke, desert scenes and atmospheric effects, such as shafts of light. These phenomena have the common feature that then are consist of the effects of small particles. To create realistic images, physical based simulation and rendering are required. In particular, the color greatly depends on the properties of light scattering due to particles. In general, however, the simulation and rendering of these images is assumed to be vets time-consuming. This paper describes efficient methods for creating realistic images of such natural phenomena.
  • Y Dobashi, K Kaneda, H Yamashita, T Okita, T Nishita
    SIGGRAPH 2000 CONFERENCE PROCEEDINGS 19 - 28 0097-8930 2000 [Refereed][Not invited]
     
    This paper proposes a simple and computationally inexpensive method for animation of clouds. The cloud evolution is simulated using cellular automaton that simplifies the dynamics of cloud formation. The dynamics are expressed by several simple transition rules and their complex motion can be simulated with a small amount of computation. Realistic images are then created using one of the standard graphics APIs, OpenGL. This makes it possible to utilize graphics hardware, resulting in fast image generation. The proposed method can realize the realistic motion of clouds, shadows cast on the ground, and shafts of light through clouds.
  • Y Dobashi, K Kaneda, H Yamashita, T Okita, T Nishita
    SIGGRAPH 2000 CONFERENCE PROCEEDINGS 19 - 28 0097-8930 2000 [Refereed][Not invited]
     
    This paper proposes a simple and computationally inexpensive method for animation of clouds. The cloud evolution is simulated using cellular automaton that simplifies the dynamics of cloud formation. The dynamics are expressed by several simple transition rules and their complex motion can be simulated with a small amount of computation. Realistic images are then created using one of the standard graphics APIs, OpenGL. This makes it possible to utilize graphics hardware, resulting in fast image generation. The proposed method can realize the realistic motion of clouds, shadows cast on the ground, and shafts of light through clouds.
  • Y Dobashi, T Yamamoto, T Nishita
    EIGHTH PACIFIC CONFERENCE ON COMPUTER GRAPHICS AND APPLICATIONS, PROCEEDINGS 31 - + 2000 [Refereed][Not invited]
     
    Recently, graphics hardware has increased in capability, and is, moreover, now available even on standard PCs. These advances have encouraged researchers to develop hardware-accelerated methods for rendering realistic images. One of the important elements in enhancing reality is the effect of atmospheric scattering. The scattering of light due to atmospheric particles has to be taken into account in order to display shafts of light produced by studio spotlights and headlights of automobiles for example. The purpose of this paper is to develop a method for displaying shafts of light at interactive rates by making use of the graphics hardware. The method makes use of hardware-accelerated volume rendering techniques to display the shafts of light.
  • Tomoyuki Nishita, Yoshinori Dobashi
    7th Pacific Conference on Computer Graphics and Applications (PG '99), 5-7 October 1999, Seoul, Korea IEEE Computer Society 218  1999 [Refereed][Not invited]
  • Y Dobashi, T Nishita, H Yamashita, T Okita
    VISUAL COMPUTER 15 (9) 471 - 482 0178-2789 1999 [Refereed][Not invited]
     
    We propose modeling that uses metaballs to create realistic clouds from satellite images. The method is intended for space flight simulators, visualization of the weather information, and simulation of surveys of the earth, The density distribution inside the clouds is defined by a set of metaballs. The parameters (center positions, radii, and density values) are automatically determined so that the synthesized image is similar to the satellite image. We also propose an animation method for clouds generated by a sequence of satellite images taken at a given interval. We give several examples of clouds generated from satellite images of typhoons passing through Japan.
  • Y Dobashi, Cingoski, V, K Kaneda, H Yamashita, T Nishita
    IEEE TRANSACTIONS ON MAGNETICS 34 (5) 3431 - 3434 0018-9464 1998/09 [Refereed][Not invited]
     
    Animation of a time-varying 3-D scalar field distribution requires generation of a set of images at a sampled time intervals i.e. frames. Although, volume rendering method can be very advantageous for such 3-D scalar field visualizations, in case of animation, the computation time needed for generation of the entire set of images call be considerably long. To address this problem, this paper proposes a fast volume rendering method which utilizes orthonormal wavelets. The coherency between frames, in the proposed method, is eliminated by expanding the scalar field into a series of wavelets. Application of the proposed method for time-varying eddy-current density distribution inside an aluminum plate (TEAM Workshop Problem 7) is given.
  • Y Dobashi, T Nishita, H Yamashita, T Okita
    PACIFIC GRAPHICS '98, PROCEEDINGS 53 - + 1998 [Refereed][Not invited]
     
    This paper proposes an image-based modeling of clouds where realistic clouds are created from satellite images using metaballs. The intention of the paper is for applications to space flight simulators, the visualization of the weather information, and the simulation of surveys of the earth. In the proposed method, the density distribution inside the clouds is defined by a set of metaballs. Parameters of metaballs, such as center positions, radii, and density values, are automatically determined so that a synthesized image of clouds modeled by using metaballs is similar to the original satellite image. We also propose an animation method for clouds generated by a sequence of satellite images taken at some interval. The usefulness of the proposed method is demonstrated by several examples of clouds generated from satellite images of typhoons passing through Japan.
  • Y Dobashi, T Nishita, K Kaneda, H Yamashita
    JOURNAL OF VISUALIZATION AND COMPUTER ANIMATION 8 (2) 115 - 127 1049-8907 1997/04 [Refereed][Not invited]
     
    Computer graphics are being used for visual environmental assessment or architectural designs. Displaying the sky as a background is indispensable in generating photorealistic images for such applications. In this paper, we propose a fast display method of the sky colour by expressing the intensity distribution of the sky using basis functions, even if the sun position and/or the camera position are altered. In the proposed method, cosine functions are used as basis functions. The sun altitude is altered at certain intervals and the distributions of the sky colour for each sun altitude are precalculated and stored efficiently using basis functions. The colour of the sky in the view direction of an arbitrary sun position can be obtained from the stored distributions and displayed quickly. (C) 1997 by John Wiley & Sons, Ltd.
  • T Nishita, H Iwasaki, Y Dobashi, E Nakamae
    COMPUTER GRAPHICS FORUM 16 (3) C357 - + 0167-7055 1997 [Refereed][Not invited]
     
    The display of natural scenes such as mountains, trees, the earth as viewed from space, the sea, and waves have been attempted. Here a method to realistically display snow is proposed. In order to achieve this, two important elements have to be considered, namely the shape and shading model of snow, based on the physical phenomenon. In this paper, a method for displaying snow fallen onto objects, including curved surfaces and snow scattered by objects, such as skis, is proposed. Snow should be treated as particles with a density distribution since it consists of water particles, ice particles, and air molecules. In order to express the material property of snow, the phase functions of the particles must be taken into account, and it is well-known that the color of snow is white because of the multiple scattering of light. This paper describes a calculation method for light scattering due to snow particles taking into account both multiple scattering and sky light, and the modeling of snow.
  • T. Sato, N. Takada, Y. Dobashi, M. Suzuki, M. Ouchi, Y. Abe
    Japanese Journal of Thoracic Diseases 35 (8) 888 - 893 0301-1542 1997 [Refereed][Not invited]
     
    A 25-year-old, previously healthy man was referred to us because of fever, left-sided chest pain, and an abnormal mass shadow at the left pulmonary hilum on chest X-ray films. Laboratory tests and fiberoptic bronchoscopy revealed no abnormality. Thoracotomy was done because a mediastinal tumor was suspected. Surgery revealed that the left lingula was atelectatic and that the mass was in the left S4, not in the mediastinum. Pathological examination of tissue from the partially resected lung showed sulfur granules, and a diagnosis of pulmonary actinomycosis was made. At least 80 cases of pulmonary actinomycosis were reported in Japan between 1963 and 1995. Pulmonary actinomycosis is most common among men in the fifth and sixth decades of life, and almost all patients have oral disease. Pulmonary actinomycosis is often difficult to distinguish from lung cancer, because both appear as mass shadows on X-ray films, and almost all cases of pulmonary actinomycosis are diagnosed by thoracotomy.
  • T Nishita, H Iwasaki, Y Dobashi, E Nakamae
    COMPUTER GRAPHICS FORUM 16 (3) C357 - + 0167-7055 1997 [Refereed][Not invited]
     
    The display of natural scenes such as mountains, trees, the earth as viewed from space, the sea, and waves have been attempted. Here a method to realistically display snow is proposed. In order to achieve this, two important elements have to be considered, namely the shape and shading model of snow, based on the physical phenomenon. In this paper, a method for displaying snow fallen onto objects, including curved surfaces and snow scattered by objects, such as skis, is proposed. Snow should be treated as particles with a density distribution since it consists of water particles, ice particles, and air molecules. In order to express the material property of snow, the phase functions of the particles must be taken into account, and it is well-known that the color of snow is white because of the multiple scattering of light. This paper describes a calculation method for light scattering due to snow particles taking into account both multiple scattering and sky light, and the modeling of snow.
  • Tomoyuki Nishita, Yoshinori Dobashi, Eihachiro Nakamae
    Proceedings of the 23rd Annual Conference on Computer Graphics and Interactive Techniques, SIGGRAPH 1996 379 - 386 1996/08/01 [Refereed][Not invited]
     
    Methods to display realistic clouds are proposed. To display realistic images, a precise shading model is required: Two components should be considered. One is multiple scattering due to particles in clouds, and the other factor to be considered is sky light. For the former, the calculation of cloud intensities has been assumed to be complex due to strong forward scattering. However, this paper proposes an efficient calculation method using these scattering characteristics in a positive way. The latter is a very significant factor when sky light is rather stronger than direct sunlight, such as at sunset/sunrise, even though sky light has been ignored in previous methods. This paper describes an efficient calculation method for light scattering due to clouds taking into account both multiple scattering and sky light, and the modeling of clouds.
  • Y Dobashi, K Kaneda, H Yamashita, T Nishita
    COMPUTER GRAPHICS FORUM 15 (3) C109 - + 0167-7055 1996 [Refereed][Not invited]
     
    Recently, computer graphics are frequently used for both architectural design and visual environmental assessment. Using computer graphics, designers can easily compare the effect of the natural light on their architectural designs under various conditions, such as different times of day, seasons, atmospheric conditions (clear or overcast sky) or building wall materials. In traditional methods of calculating the luminance due to sky light, however, all calculation must be performed from scratch if such conditions undergo change. Therefore, to compare the architectural designs under different conditions, a great deal of time has to be spent on generating the images. This paper proposes a new method of quickly generating images of an outdoor scene, taking into account glossy specular reflection, even if such conditions change. In this method, luminance due to sky light is expressed by a series of basis functions, and basis luminances corresponding to each basis function are precalculated and stored in a compressed form in the preprocess. Once the basis luminances are calculated, the luminance due to sky light can be quickly calculated by the weighted sum of the basis luminances. Several examples of an architectural design demonstrate the usefulness of the proposed method.
  • T. Kawasaki, T. Gotoh, T. Nakamura, S. Hashimoto, T. Arimoto, Y. Iwasaki, M. Ono, S. Toda, Y. Dobashi, M. Nakagawa
    Japanese Journal of Thoracic Diseases 34 (11) 1244 - 1248 0301-1542 1996 [Refereed][Not invited]
     
    A 70-year-old woman wad admitted to our hospital complaining of hoarseness. Bronchoscopic examination revealed that the left vocal cord was fixed in the paramedian postion, and therefore left recurrent nerve paralysis was suspected. Although a chest X-ray film showed no abnormal findings, a chest computed tomogram showed that pretracheal (3) and subaortic (5) lymph nodes were swollen (1 to 2 cm in diameter). An open biopsy was done. Histological examination of the resected mediastinal lymph nodes revealed an accumulation of Langhans giant cells and epithelioid cells in caseous necrosis. An acid-fast bacillus was seen after Ziehl-Neelsen staining. This was a rare case of mediastinal tuberculous lymphadenitis in which hoarseness was useful for early diagnosis. Fifty-three cases of tuberculous mediastinal lymphadenitis have been reported in Japan.
  • K Kaneda, Y Dobashi, K Yamamoto, H Yamashita
    1996 SYMPOSIUM ON VOLUME VISUALIZATION, PROCEEDINGS 7 - & 1996 [Refereed][Not invited]
     
    In scientific visualization, it is necessary to visualize the distribution of a scalar field by using adjustable color maps in conjunction with a pseudo-color display. This paper proposes a method for fast direct volume rendering when color maps undergo change. The method pre-calculates basis images that are independent from the color maps. The rendered images for an arbitrary color map are then generated by compositing the basis images. The proposed method makes possible interactive observation of changing color maps with a fixed viewpoint.
  • Tomoyuki Nishita, Yoshinori Dobashi, Eihachiro Nakamae
    SIGGRAPH 1996 379 - 386 1996 [Refereed][Not invited]
  • Y Dobashi, K Kaneda, H Yamashita, T Nishita
    COMPUTER GRAPHICS FORUM 15 (3) C109 - + 0167-7055 1996 [Refereed][Not invited]
     
    Recently, computer graphics are frequently used for both architectural design and visual environmental assessment. Using computer graphics, designers can easily compare the effect of the natural light on their architectural designs under various conditions, such as different times of day, seasons, atmospheric conditions (clear or overcast sky) or building wall materials. In traditional methods of calculating the luminance due to sky light, however, all calculation must be performed from scratch if such conditions undergo change. Therefore, to compare the architectural designs under different conditions, a great deal of time has to be spent on generating the images. This paper proposes a new method of quickly generating images of an outdoor scene, taking into account glossy specular reflection, even if such conditions change. In this method, luminance due to sky light is expressed by a series of basis functions, and basis luminances corresponding to each basis function are precalculated and stored in a compressed form in the preprocess. Once the basis luminances are calculated, the luminance due to sky light can be quickly calculated by the weighted sum of the basis luminances. Several examples of an architectural design demonstrate the usefulness of the proposed method.
  • Y DOBASHI, K KANEDA, H NAKATANI, H YAMASHITA, T NISHITA
    COMPUTER GRAPHICS FORUM 14 (3) C229 - + 0167-7055 1995/08 [Refereed][Not invited]
     
    When designing interior lighting effects, it is desirable to compare a variety of fighting designs involving different lighting devices and directions of light. It is, however, time-consuming to generate images with many different lighting parameters, taking interreflection into account, because all luminances must be calculated and recalculated. This makes it difficult to design lighting effects interactively. To address this problem, this paper proposes a method of quickly generating images of a given scene illustrating an interreflective environment illuminated by sources with arbitrary luminous intensity distributions. In the proposed method, the luminous intensity ditribution is expressed with basis functions. The proposed method uses a series of spherical harmonic functions as basis functions, and calculates in advance each intensity on surfaces lit by the light sources whose luminous intensity distribution are the same as the spherical harmonic functions. The proposed method makes it possible to generate images so quickly that we can change the luminous intensity distribution interactively. Combining the proposed method with an interactive walk-through that employs intensity mapping, an interactive system for lighting design is implemented. The usefulness of the proposed method is demonstrated by its application to interactive lighting design, where many images are generated by altering lighting devices and/or direction of light.
  • Yoshinori Dobashi, Kazufumi Kaneda, Hideki Nakatani, Hideo Yamashita, Tomoyuki Nishita
    Computer Graphics Forum 14 (3) 229 - 240 1467-8659 1995 [Refereed][Not invited]
     
    When designing interior lighting effects, it is desirable to compare a variety of lighting designs involving different lighting devices and directions of light. It is, however, time‐consuming to generate images with many different lighting parameters, taking interreflection into account, because all luminances must be calculated and recalculated. This makes it difficult to design lighting effects interactively. To address this problem, this paper proposes a method of quickly generating images of a given scene illustrating an interreflective environment illuminated by sources with arbitrary luminous intensity distributions. In the proposed method, the luminous intensity ditribution is expressed with basis functions. The proposed method uses a series of spherical harmonic functions as basis functions, and calculates in advance each intensity on surfaces lit by the light sources whose luminous intensity distribution are the same as the spherical harmonic functions. The proposed method makes it possible to generate images so quickly that we can change the luminous intensity distribution interactively. Combining the proposed method with an interactive walk‐through that employs intensity mapping, an interactive system for lighting design is implemented. The usefulness of the proposed method is demonstrated by its application to interactive lighting design, where many images are generated by altering lighting devices and/or direction of light. © 1995 Eurographics Association
  • Y DOBASHI, K KANEDA, T NAKASHIMA, H YAMASHITA, T NISHITA, K TADAMURA
    COMPUTER GRAPHICS FORUM 13 (3) C85 - & 0167-7055 1994/09 [Refereed][Not invited]
     
    It is inevitable for indoor lighting design to render a room lit by natural light, especially for an atelier or an indoor pool where there are many windows. This paper proposes a method for calculating the illuminance due to natural light, i.e. direct sunlight and skylight, passing through transparent planes such as window glass. The proposed method makes it possible to efficiently calculate such illuminance accurately, because it takes into account both non-uniform luminous intensity distribution of skylight and the distribution of transparency of glass according to incident angles of light. Several examples including the lighting design in an indoor pool, are shown to demonstrate the usefulness of the proposed method.
  • Y DOBASHI, K KANEDA, T NAKASHIMA, H YAMASHITA, T NISHITA, K TADAMURA
    COMPUTER GRAPHICS FORUM 13 (3) C85 - & 0167-7055 1994/09 [Refereed][Not invited]
     
    It is inevitable for indoor lighting design to render a room lit by natural light, especially for an atelier or an indoor pool where there are many windows. This paper proposes a method for calculating the illuminance due to natural light, i.e. direct sunlight and skylight, passing through transparent planes such as window glass. The proposed method makes it possible to efficiently calculate such illuminance accurately, because it takes into account both non-uniform luminous intensity distribution of skylight and the distribution of transparency of glass according to incident angles of light. Several examples including the lighting design in an indoor pool, are shown to demonstrate the usefulness of the proposed method.

Books etc

  • 三谷, 純, 高山, 健志, 土橋, 宜典, 向井, 智彦, 藤澤, 誠 
    コロナ社 2023/07 (ISBN: 9784339013719) x, 242p
  • 土橋, 宜典, 鍛冶, 静雄, Symposium : Mathematical Progress in Expressive Image Synthesis 
    Institute of Mathematics for Industry, Kyushu University : Graduate School of Mathematics, Kyushu University 2016 v, 82 p.
  • 落合, 啓之, 土橋, 宜典, Symposium : Mathematical Progress in Expressive Image Synthesis 
    Institute of Mathematics for Industry Kyushu University : Graduate School of Mathematics, Kyushu University 2015 vi, 124 p.
  • 安生, 健一, 落合, 啓之, 土橋, 宜典, 溝口, 佳寛, 鍛冶, 静雄, Symposium: Mathematical Progress in Expressive Image Synthesis 
    九州大学マス・フォア・インダストリ研究所 : 九州大学大学院数理学研究院グローバルCOEプログラム「マス・フォア・インダストリ教育研究拠点」 2013 vi, 154 p.
  • Jim Blinn's Corner 日本語版(2) Dirty Pixels
    西田, 三浦, 土橋, 有我, 望月, 中里, 橋本 (Contributor)
    オーム社 2004
  • Jim Blinn's Corner 日本語版(1) A Trip Down the Graphics Pipeline
    西田, 三浦, 土橋, 有我, 望月, 中里, 橋本 (Contributor)
    オーム社 2004

MISC

  • 藤真太郎, 佐藤周平, 佐藤周平, 岩崎慶, 岩崎慶, 土橋宜典, 土橋宜典  情報処理学会研究報告(Web)  2023-  (CG-191)  2023
  • 笹晃輔, 土橋宜典, 佐藤周平  情報処理学会研究報告(Web)  2022-  (CG-185)  2022
  • 水嶋楓華, 佐藤周平, 櫻井快勢, 土橋宜典, 高尚策, 唐政  情報処理学会研究報告(Web)  2021-  (CG-184)  2021
  • 齊藤彪雅, 佐藤周平, 土橋宜典  情報処理学会研究報告(Web)  2021-  (CG-184)  2021
  • 大場誉幸, 佐藤周平, 土橋宜典  情報処理学会研究報告(Web)  2021-  (CG-184)  2021
  • 笹晃輔, 佐藤周平, 土橋宜典  情報処理学会研究報告(Web)  2020-  (CG-178)  2020
  • 佐藤周平, 佐藤周平, 土橋宜典, 土橋宜典  情報処理学会研究報告(Web)  2020-  (CG-179)  2020
  • 齊藤彪雅, 佐藤周平, 土橋宜典, 高尚策, 唐政  情報処理学会研究報告(Web)  2020-  (CG-180)  2020
  • 佐藤周平, 佐藤周平, 土橋宜典, 土橋宜典, KIM Theodore  情報処理学会研究報告(Web)  2019-  (CG-175)  2019
  • パッチ合成に基づく詳細な動きを保持した流体の流れの変形
    佐藤 周平, 土橋 宜典, 櫻井 快勢, 西田 友是  Visual Computing 2018 ポスター  2018/06  [Not refereed][Not invited]
  • 渡辺優太, 佐藤周平, 土橋宜典, 山本強  情報処理学会研究報告(Web)  2017-  (DCC-17)  Vol.2017‐DCC‐17,No.5,1‐4 (WEB ONLY)  2017/11  [Not refereed][Not invited]
  • 土橋宜典, 土橋宜典, 岩崎慶, 岡部誠, 井尻敬, 藤堂英樹  情報処理学会研究報告(Web)  2017-  (DCC-17)  Vol.2017‐DCC‐17,No.25,1‐5 (WEB ONLY)  2017/11/01  [Not refereed][Not invited]
  • 渡辺優太, 佐藤周平, 土橋宜典, 山本強  電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM)  2017-  ROMBUNNO.153  2017/10  [Not refereed][Not invited]
  • 有働 篤人, 青木 直史, 土橋 宜典, 山本 強  聴覚研究会資料 = Proceedings of the auditory research meeting  47-  (5)  361  -364  2017/07/20  [Not refereed][Not invited]
  • 松永 悠斗, 青木 直史, 土橋 宜典, 山本 強  聴覚研究会資料 = Proceedings of the auditory research meeting  47-  (5)  355  -360  2017/07/20  [Not refereed][Not invited]
  • 菊池 雄大, 青木 直史, 土橋 宜典, 山本 強  聴覚研究会資料 = Proceedings of the auditory research meeting  47-  (5)  349  -354  2017/07/20  [Not refereed][Not invited]
  • 有働 篤人, 青木 直史, 土橋 宜典, 山本 強  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (138)  103  -106  2017/07/20  [Not refereed][Not invited]
  • 松永 悠斗, 青木 直史, 土橋 宜典, 山本 強  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (138)  97  -102  2017/07/20  [Not refereed][Not invited]
  • 菊池 雄大, 青木 直史, 土橋 宜典, 山本 強  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (138)  91  -96  2017/07/20  [Not refereed][Not invited]
  • 佐藤周平, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2017-  ROMBUNNO.17  2017/06  [Refereed][Not invited]
  • 佐藤周平, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2017-  ROMBUNNO.26  2017/06  [Not refereed][Not invited]
  • 櫻井快勢, 土橋宜典, 土橋宜典, 西田友是, 西田友是  情報処理学会全国大会講演論文集  79th-  (4)  2017
  • 井尻敬, 井尻敬, 藤堂英樹, 小檜山賢二, 平林晃, 土橋宜典, 土橋宜典  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2017-  2017
  • 山河 卓也, 土橋 宜典, 山本 強  映像情報メディア学会技術報告 = ITE technical report  40-  (27)  1  -4  2016/08  [Not refereed][Not invited]
  • 須田 祥平, 山本 強, 土橋 宜典  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  116-  (122)  41  -44  2016/07/07  [Not refereed][Not invited]
  • 櫻井快勢, YUE Yonghao, 金森由博, 岩崎慶, 岩崎慶, 土橋宜典, 土橋宜典, 西田友是, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2016-  ROMBUNNO.04  2016/06/18  [Not refereed][Not invited]
  • 佐藤周平, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2016-  ROMBUNNO.14  2016/06  [Refereed][Not invited]
  • Kikuta Hayato, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2016-  (2)  129  -129  2016/03/01  [Not refereed][Not invited]
  • Shiraishi Kenichi, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2016-  (2)  176  -176  2016/03/01  [Not refereed][Not invited]
  • Suda Shohei, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2016-  (1)  173  -173  2016/03/01  [Not refereed][Not invited]
  • 井尻敬, 岩崎慶, 岡部誠, 藤堂英樹, 土橋宜典, 西村智, PODEE Namo  画像電子学会誌(CD-ROM)  45-  (1)  124‐125  2016/01/30  [Not refereed][Not invited]
  • 名畑豪祐, 岩崎慶, 土橋宜典, 土橋宜典, 西田友是, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2015-  ROMBUNNO.12  2015/06/27  [Not refereed][Not invited]
  • 佐藤周平, 土橋宜典, 土橋宜典, 土橋宜典, YUE Yonghao, 岩崎慶, 岩崎慶, 西田友是, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2015-  ROMBUNNO.11  2015/06/27  [Not refereed][Not invited]
  • 佐藤周平, 土橋宜典, YUE Yonghao, 岩崎慶, 西田友是  情報処理学会全国大会講演論文集  77th-  (4)  4.57-4.58  2015/03/17  [Not refereed][Not invited]
  • 佐藤 周平, 土橋 宜典, 楽 詠灝, 岩崎 慶, 西田 友是  第77回全国大会講演論文集  2015-  (1)  57  -58  2015/03/17  [Not refereed][Not invited]
     
    近年，映画やゲームなどにおいて，流体シミュレーションを用いた映像制作が盛んに行われている．このような映像制作では，特にSFやファンタジー 映画において，物理シミュレーションを用いつつも，現実では起こりえないような流体の映像が求められる．このような場合，流体の流れ場を変形する ことで，そのような映像の容易な作成が期待できる．しかし，単純に流れ場を変形した場合，流体が満たすべき物理法則である質量保存，運動量保存を 満たすことができない．特に，質量保存が満たされない場合，意図しない場所から流体が湧き出るなど，視覚的に問題となる場合が多い．そこで本手法 では，2つの物理法則のうち質量保存，すなわち流体の非圧縮性を保った流れ場の変形を実現する．
  • Kikuta Hayato, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2015-  (2)  115  -115  2015/02/24  [Not refereed][Not invited]
  • 大津 久平, 楽 詠コウ, 侯 啓明, 岩崎 慶, 土橋 宜典, 須田 礼二, 西田 友是  情報処理学会研究報告. グラフィクスとCAD研究会報告  2015-  (2)  1  -7  2015/02/20  [Not refereed][Not invited]
     
    写実的な画像を生成するための大域照明計算はコンピュータグラフィックスにおいて重要な分野である.近年,マルコフ連鎖モンテカルロ法を用いた大域照明計算法が活発に研究,開発されている.例えば,マルコフ連鎖モンテカルロ法 (MCMC) を用いるレンダリング手法の一つであるメトロポリス光輸送法 (MLT) はある規則に従って光路を変異させながら,光路空間におけるエネルギーの寄与分布に従うようなマルコフ連鎖を生成する.MCMC を用いるレンダリング手法では,サンプルが次元の境界を超える際に次元間変異が用いられる.例えば,MLT では次元間変異として双方向変異法を用い,光路の長さや構造を変異させる.このような次元間変異手法はしばしばサンプル過程のエルゴード性を保つために用いられ,いくつかの手法にとっては次元間変異は必須である.しかしながら MCMC を用いたレンダリングにおいて,次元間変異の効率を改善するための研究はほとんど試されてこなかった.そこで,本稿では,双方向変異法の効率の改良について考察する.重点的サンプリングに類似した考え方に基づく双方向変異法の効率についての解析から,光路サンプリング戦略の決定を行う分布の制御によって,双方向変異法の採択確率を向上できることが分かる.この解析に基づき,我々は焼きなまし法を用いて採択確率の期待値を最大化することで光路サンプリング戦略の決定分布を効率化する手法を提案する.この手法を用いることにより,双方向変異法の特徴を残しながら高い遷移確率で光路をサンプリングすることができる.
  • 岩崎慶, 土橋宜典, 岡部誠, 山本強  Meeting of Federation of Imaging Societies (CD-ROM)  2nd-  ROMBUNNO.PC10  2015  [Not refereed][Not invited]
  • 名畑 豪祐, 岩崎 慶, 土橋 宜典, 西田 友是  IPSJ Journal  55-  (12)  2559  -2568  2014/12/15  [Not refereed][Not invited]
     
    In this paper, we propose an efficient ray tracing method based on divide-and-conquer approach. Previous divide-and-conquer ray tracing (DACRT) methods subdivide intersection problems between large numbers of rays and primitives, by recursively subdividing the problem size based on the distribution of primitives only, until it can be easily solved. To subdivide the intersection problems, the lack of considering the distribution of rays can decrease the rendering performance, especially for high resolution images with antialiasing. To address this problem, our method exploits the distribution of rays for subdivision of intersection problems, construction of acceleration data structure, and determination of ray traversal order. To accelerate ray traversals, we have derived a new cost metric which is used to avoid inefficient subdivision of the intersection problem where the number of rays is not sufficiently reduced at the cost of expensive intersection tests between rays and bounding volumes. The cost metric is easy to calculate and hence easy to implement. Our method can accelerate the tracing of many types of rays by a factor of up to two. In addition, we show that our method can reduce the number of intersection tests between rays and bounding volumes compared to the state-of-the-art DACRT method.
  • 谷 翼, 土橋 宜典, 佐藤 周平, 山本 強  研究報告グラフィクスとCAD（CG）  2014-  (22)  1  -6  2014/11/13  [Not refereed][Not invited]
     
    近年，コンピュータグラフィックス (CG) の進歩により，映画やゲーム，アニメなど様々な場面において，CG が多く用いられるようになっている．これら CG における映像生成の手段の一つとして，流体シミュレーションにより物理現象を再現する研究が広く行われている．しかし，写実的な映像を生成するためには，高精度なシミュレーションが必要となり，計算コストが膨大なものになってしまう．そこで本研究では，流体シミュレーションから得られた 2 つの密度場を変形及び合成することで，それらの中間となる形状を補間する手法を提案する．
  • Yonghao Yue, Kei Iwasaki, Bing-yu Chen, Yoshinori Dobashi, Tomoyuki Nishita  IPSJ SIG Notes  2014-  (1)  1  -1  2014/09/09  
    We present a technique for computing the shape of a transparent object that can generate user-defined caustic patterns. The surface of the object generated using our method is smooth. Thanks to this property, the resulting caustic pattern is smooth, natural, and highly detailed compared to the results obtained using previous methods. Our method consists of two processes. First, we use a differential geometry approach to compute a smooth mapping between the distributions of the incident light and the light reaching the screen. Second, we utilize this mapping to compute the surface of the object. We solve Poisson's equation to compute both the mapping and the surface of the object.
  • 佐藤周平, 土橋宜典, 岩崎慶, 落合啓之, 山本強  電子情報通信学会論文誌 D(Web)  J97-D-  (9)  1528-1536 (WEB ONLY)  2014/09/01  [Not refereed][Not invited]
  • TANI TSUBASA, DOBASHI YOSHINORI, SATO SYUHEI, YAMAMOTO TSUYOSHI  情報科学技術フォーラム講演論文集  13-  (3)  177  -178  2014/08/19  [Not refereed][Not invited]
  • 名畑豪祐, 岩崎慶, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2014-  ROMBUNNO.13  2014/06/29  [Not refereed][Not invited]
  • Syuhei Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto, Tomoyuki Nishita  IPSJ SIG Notes  2014-  (13)  1  -5  2014/06/21  [Not refereed][Not invited]
     
    Recently, realistic fluid animations are often used in movies or video games. These fluid animations are usually generated by using fluid simulation, but computational costs are too expensive for creating realistic animations. Therefore, if the user would like to obtain results different from simulated results, the user must execute fluid simulation repeatedly and must take a long time. To address this problem, this paper proposes a method for interpolating between two different velocity fields of fluid. By using our system, the user can create various fluid animations from the two input velocity fields, without executing fluid simulation. In our method, control points are placed at the positions where features of these two velocity fields are similar, we interpolate between these control points by using polar interpolation. Then, by deforming the two velocity fields following the interpolated control points, plausible velocity fields are interpolated.
  • Keisuke Mizutani, Syuhei Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2014-  (8)  1  -3  2014/06/21  [Not refereed][Not invited]
     
    In this paper we present a method for controlling fire simulation based on computational fluid dynamics. Our method applies a previous method for controlling smoke simulation to fire simulation. However, controlling fire simulation is difficult when using the previous method, because in the fire simulation, strong buoyancy forces caused by high-temperature of fire are arisen. To address this problem, our method locally adjusts a parameter of control forces in the previous method using a difference between the user-specified target shape and the simulated fire shape. Our method can control the fire into an arbitrary shape specified by the user.
  • Generating Flow Fields Variations using Laplacian Eigenfunctions
    Syuhei Sato, Yoshinori Dobashi, Kei Iwasaki, Hiroyuki Ochiai, Tsuyoshi Yamamoto  Mathematical Progress in Expressive Image Synthesis Ⅰ  93  -101  2014/06  [Refereed][Not invited]
  • Okada Goro, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2014-  (2)  13  -13  2014/03/04  [Not refereed][Not invited]
  • Dobashi Yoshinori  Journal of the Illuminating Engineering Institute of Japan  98-  (3)  136  -139  2014/03  
    One of the ultimate goals of computer graphics is to create realistic virtual environments. Rendering realistic images of the virtual environments is a key element to achieve this goal. In order to synthesize realistic images, we need to accurately simulate interactions of light with virtual objects while taking into account interreflections of light or global illumination effects. Global illumination is the major research topic in computer graphics and has a long research history. In early days, global illumination was simulated under simplified assumptions such as diffuse surfaces only. However, recent advancement in computer performance makes us possible to handle much more general situations, such as specular/transparent surfaces or moving objects, and many methods have been proposed. These methods can be classified into two approaches; precomputation-based or precomputation-free approaches. In this article, we will review several methods for these two approaches and discuss the future of the researches on the realistic images synthesis.
  • TADA Munehiro, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  The IEICE transactions on information and systems (Japanese edition)  97-  (3)  676  -686  2014/03  [Not refereed][Not invited]
     
    コンピュータグラフィックスにおいて,シェーディング技術は仮想物体の見え方を決定する重要な要素である.しかし,物理現象を正確にシミュレーションしたシェーディング計算はコストが高い.そこで,比較的低コストながら高品質な画像を生成する手法として,環境マッピングという技術が提案されている.しかし,必ずしも意図した結果が得られるとは限らない.そこで,これまで環境マップ自体に編集を施すことで目的の陰影効果を表現する手法が幾つか提案されている.しかし,これらの手法では局所的に陰影の編集を行うといった効果は実現できない.本論文では目的の位置に目的の輝度を直接指定することで,シェーディング結果を容易に編集することができるシステムを提案する.提案システムでは,ユーザが指定した輝度を補間することで輝度計算を行う.この補間には,ユーザが指定した点の特徴量を用いる.ユーザは補間に用いる特徴量を自由に選ぶことにより,シェーディング結果に対して直感的な編集を施すことができる.この際,特徴量として計算点の座標を用いることで,局所的な陰影の編集を可能とした.
  • 福本 和哉, 山本 強, 土橋 宜典  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  113-  (433)  253  -258  2014/02/17  [Not refereed][Not invited]
  • 岡田 悟郎, 土橋 宜典, 山本 強  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  113-  (433)  259  -264  2014/02/17  [Not refereed][Not invited]
  • 葛西 哲, 土橋 宜典, 山本 強  研究報告グラフィクスとCAD（CG）  2014-  (9)  1  -6  2014/02/13  [Not refereed][Not invited]
     
    CG において影はシーンやキャラクターの印象に大きく影響を与える重要な役割を持っている．しかし，影をデザインするためには光源の位置，向き，大きさといった様々なパラメータを調整する必要がある．そのため，専門的な技術を持たない初心者が所望の影をデザインするには非常に煩雑な作業を必要とする．本稿はソフトシャドウを含む影をインタラクティブに編集出来るシステムを提案する．提案システムでは，陰影や影の位置の移動といった物理法則に従った編集から，影を曲げる・引き延ばすといった物理法則に従わない編集操作まで行うことが出来る．ユーザはマウス操作を用いた直感的な指定から，これらの効果を簡単に実現することが出来る．Shadows are important visual clues for computer graphics. In order to obtain user-desired results, the user is required to adjust many parameters of light such as intensity, direction, and size. Then, the shadow-design process is often difficult and tedious for novice users. In this research, we propose an interactive editing system for shadows. Our system can create both physically-correct and incorrect results. In our system, the user can design shadows by intuitive operations.
  • 福本 和哉, 山本 強, 土橋 宜典  映像情報メディア学会技術報告 = ITE technical report  38-  (7)  253  -258  2014/02  [Not refereed][Not invited]
  • 岡田 悟郎, 土橋 宜典, 山本 強  映像情報メディア学会技術報告 = ITE technical report  38-  (7)  259  -264  2014/02  [Not refereed][Not invited]
  • Doi Munehiro, Dobashi Yoshinori, Tamori Hideaki, Yamamoto Tsuyoshi  The Journal of the Institute of Image Electronics Engineers of Japan  43-  (3)  309  -317  2014  [Not refereed][Not invited]
     
    A spacial image filter sequence is often used as a preprocess part in an image processing application and is important for enhancing features or removing unnecessary information from images. Designing such a sequence is a time-consuming work even if it is done by experienced engineers, therefore automatic generation has been studied for some decades. However, the robustness of the generated sequence and coexisting of image operations and numerical calculations in a sequence are still challenges. We propose a novel method based on a Multi-Objective Genetic Programming to generate a robust image sequence consisting of filters which processes Image-Value pairs by giving sets of images before and after processing. We demonstrate our method by generating a background elimination filter from flower pictures.
  • Yuhei Shibukawa, Yoshinori Dobashi, Tsuyoshi Yamamoto  Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers  68-  (2)  J66  -J71  2014  [Not refereed][Not invited]
     
    This paper focuses on the rendering of fluids represented by volumetric datasets. Generally, volume data can be visualized by a volume rendering technique. The result depends on the transfer function that converts volume data into colored volume. However, it is often difficult to create the desired images by manually adjusting the transfer function. We propose an intuitive system that allows the user to directly design the appearance of the volume by specifying the colors of the volume with a set of control points. The system solves an inverse problem to determine the transfer function such that the colors of the rendered image become the same as those of the control points. In our method, the transfer function is a multi-dimensional function of features computed from the input volume dataset. Our method represents the transfer function as a linear combination of radial basis functions to solve the inverse problem.
  • 水谷圭佑, 佐藤周平, 土橋宜典, 山本強  電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM)  2013-  ROMBUNNO.149  2013/10/19  [Not refereed][Not invited]
  • Kazuma Egashira, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2013-  (2)  1  -5  2013/09/02  [Not refereed][Not invited]
     
    We discuss methods for computing material and lighting information from a user-specified target image. The target image is created by using a technique called surface flow that uses a depth and a normal image computed from a 3D object. The surface flow allows us to interactively design appearances of objects. However, since the surface flow is an image-based method, the viewpoint must be fixed. We address this problem by estimating material and lighting parameters from the target image so that we can change the viewpoint by rendering the object using the estimated parameters. We develop and discuss four different methods based on inverse lighting design, histogram matching, Phong shading model, and inverse BRDF modeling.
  • Ayumu Kogawa, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2013-  (5)  1  -5  2013/09/02  [Not refereed][Not invited]
     
    Visualization of natural phenomena has become one of the most important research topics in computer graphics. In particular, visual simulation of fluid phenomena, such as water, smoke and fire, has attracted many researchers' attentions. One of the common approaches to the simulation of fluid phenomena is to numerically solve equations governing the fluid motion. However, in order to obtain desired visual effects, users have to adjust many simulation parameters by a time-consuming trial and error process. Furthermore, accurate and expensive numerical simulation is required to obtain realistic results. We propose a system that efficiently creates realistic animations by applying Texture Synthesis techniques to temperature distribution obtained by fluid simulation.
  • KUSUMOTO Katsutoshi, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  The IEICE transactions on information and systems (Japanese edition)  96-  (8)  1944  -1951  2013/08/01  [Not refereed][Not invited]
     
    CGを用いて生成される映像の中でも,雲の表示は重要な要素の一つである.本論文では,綿のような形状として現れる積雲に着目し,積雲が所望の形状となるよう流体シミュレーションをコントロールする手法を提案する.積雲をシミュレーションする際,その形状や大きさはシミュレーションに使用する様々なパラメータに依存する.ユーザが意図した雲が生成されるようこれらのパラメータを手動で調節することは極めて難しい.そこで本研究では,ユーザが指定した分布の雲が自動生成されるよう流体シミュレーションをコントロールする.提案手法により,パラメータの調整に試行錯誤することなく,キーフレームで指定した所望の形状・分布に変化する積雲のアニメーション生成が可能である.
  • 水谷一貴, 岩崎慶, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2013-  ROMBUNNO.9  2013/06/22  [Not refereed][Not invited]
  • 石川知一, YUE Yonghao, 渡辺大地, 岩崎慶, 土橋宜典, 柿本正憲, 近藤邦雄, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2013-  ROMBUNNO.6  2013/06/22  [Not refereed][Not invited]
  • 佐藤周平, 土橋宜典, 岩崎慶, 山本強, 落合啓之, 落合啓之  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2013-  ROMBUNNO.5  2013/06/22  [Not refereed][Not invited]
  • Tsubasa Tani, Yoshinori Dobashi, Syuhei Sato, Tsuyoshi Yamamoto  IPSJ SIG Notes  2013-  (5)  1  -5  2013/06/17  [Not refereed][Not invited]
     
    コンピュータグラフィックス (CG) の進歩により，映画やゲーム，アニメなど様々な場面において，CG が多く用いられるようになっている．これら CG における映像生成の手段の一つとして，流体シミュレーションにより物理現象を再現する研究が広く行われている．しかし，写実的な映像を生成するためには，高精度なシミュレーションが必要となり，計算コストが膨大なものになってしまう．そこで本研究では，流体シミュレーションにより得られた結果 （3 次元テクスチャ） を合成することで，有限時間の映像を任意時間再生可能とする手法を提案する．3 次元テクスチャを複数の小領域に分割し，一部の領域のみ終端データから始端への遷移を行うことで，違和感のない映像を生成する．しかし，流体のシミュレーションデータは容量が大きいため，多くのデータを扱う場合，使用するメモリ量が膨大になってしまう．そのため，データ圧縮手法の一つであるベクトル量子化を用い，シミュレーションデータを圧縮したうえでメモリへ格納する．
  • Mikio Shinya, Yoshinori Dobashi, Kei Iwasaki, Michio Shiraishi, Tomoyuki Nishita  情報処理学会論文誌  54-  (4)  2013/04/15  
    Fast computation of multiple reflections and scattering among complex objects is very important in photorealistic rendering. This paper applies the plane-parallel scattering theory to the rendering of densely distributed objects such as trees. We propose a simplified plane-parallel scattering model that has very simple analytic solutions, allowing efficient evaluation of multiple scattering. A geometric compensation method is also introduced to cope with the infinite plane condition, required by the plane-parallel model. The scattering model was successfully applied to tree rendering. Comparison with a Monte Carlo method was made and reasonable agreement was confirmed. A rendering system based on the model was implemented and multiple inter-reflections were effectively obtained. The view-independent feature of the model allows fast display of scenes. The pre-computation is also modest, permitting interactive control of lighting conditions.------------------------------This is a preprint of an article intended for publication Journal ofInformation Processing(JIP). This preprint should not be cited. Thisarticle should be cited as: Journal of Information Processing Vol.21(2013) No.2 (online)DOI http://dx.doi.org/10.2197/ipsjjip.21.349------------------------------Fast computation of multiple reflections and scattering among complex objects is very important in photorealistic rendering. This paper applies the plane-parallel scattering theory to the rendering of densely distributed objects such as trees. We propose a simplified plane-parallel scattering model that has very simple analytic solutions, allowing efficient evaluation of multiple scattering. A geometric compensation method is also introduced to cope with the infinite plane condition, required by the plane-parallel model. The scattering model was successfully applied to tree rendering. Comparison with a Monte Carlo method was made and reasonable agreement was confirmed. A rendering system based on the model was implemented and multiple inter-reflections were effectively obtained. The view-independent feature of the model allows fast display of scenes. The pre-computation is also modest, permitting interactive control of lighting conditions.------------------------------This is a preprint of an article intended for publication Journal ofInformation Processing(JIP). This preprint should not be cited. Thisarticle should be cited as: Journal of Information Processing Vol.21(2013) No.2 (online)DOI http://dx.doi.org/10.2197/ipsjjip.21.349------------------------------
  • OTSU Hisanari, YUE Yonghao, HOU Qiming, IWASAKI Kei, CHEN Bing-Yu, DOBASHI Yoshinori, NISHITA Tomoyuki  ITE Technical Report  37-  (17)  1  -4  2013/03/08  [Not refereed][Not invited]
     
    Methods for computing global illumination using Markov Chain Monte Carlo techniques generate a new light path by locally mutating an already generated light path. Such methods can generate light paths carrying large energies in high probabilities, aiming at higher computation efficiency. However, using the mutation strategies proposed in previous methods, when the energy distribution of the light paths is highly localized (i.e., there are spiky peaks), the generated light paths tend to get stuck in such localized regions, thus the computation could be non-robust. To resolve this problem, we...
  • Naya Wataru, Fukumoto Kazuya, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2013-  (2)  125  -125  2013/03/05
  • Sato Yasuyuki, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2013-  (2)  163  -163  2013/03/05  [Not refereed][Not invited]
  • SATO Syuhei, MORITA Takuya, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  The IEICE transactions on information and systems (Japanese edetion)  96-  (2)  338  -345  2013/02/01  [Not refereed][Not invited]
     
    近年,流体解析を用いて写実的な水や炎などを表現する研究が数多く行われており,それらの方法を利用して生成された映像が映画やゲームなどに数多く用いられている.しかし,流体シミュレーションは計算コストが高く,映像制作現場で必要とされる非常に高解像度の流体映像を得るまでには多大な時間がかかってしまう.そこで本研究では,前計算により作成したデータベースを用いて,低解像度の流体シミュレーションを高解像度化することで,効率的に高解像度の流体アニメーションの作成を可能とする手法を提案する.提案法では,前処理において流体解析により得られた速度場をデータベースとして保存しておき,ユーザ所望の流れの場をデータベース内の速度場の線形和として表現することで,高解像度の流体アニメーションを効率的に生成する.
  • 楽詠こう, 大津久平, 候啓明, 岩崎慶, 陳炳宇, 土橋宜典, 西田友是  画像電子学会誌(CD-ROM)  42-  (1)  120  -121  2013/01/30  [Not refereed][Not invited]
  • 吉川宇穂, 土橋宜典, 山本強  映像情報メディア学会冬季大会講演予稿集(CD−ROM)  2012-  ROMBUNNO.2-1  2012/11/27  [Not refereed][Not invited]
  • Syuhei Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2012-  (8)  1  -5  2012/11/26  [Not refereed][Not invited]
     
    Recently, realistic fluid animations are often used in movies or TV games. These fluid animations are usually generated by using fluid simulation. However, it is difficult to generate desired animations by only adjusting parameters used in the fluid simulation. To address this problem, this paper proposes a method for extending and retracting a simulation space of fluid. Our method uses laplacian eigen functions to generate velocity fields that satisfy the fluid equations in the deformed simulation space.
  • Takuya Morita, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2012-  (9)  1  -6  2012/11/26  [Not refereed][Not invited]
     
    Recently, many methods for creating fluid animation based on fluid simulation have been proposed. We focus on the simulation of explosions. Some methods for simulating explosion were already developed. Although these methods can create realistic shapes and movement of explosions, the resulting shapes and motion depend on many simulation parameters. Therefore, it is very difficult to create the explosions with desired shapes. In this paper, we propose a system for controlling explosion shapes towards desired shapes. Our system consists of the following two steps: scale-optimization step and ...
  • 福本和哉, 納谷航, 山本強, 土橋宜典  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.121  2012/10/20  [Not refereed][Not invited]
  • XING Xiaoxiong, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.129  2012/10/20  [Not refereed][Not invited]
  • ZHANG Yongsheng, YAMAMOTO Tsuyoshi, DOBASHI Yoshinori  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.159  2012/10/20  [Not refereed][Not invited]
  • 山上晃平, 山本強, 土橋宜典  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.105  2012/10/20  [Not refereed][Not invited]
  • 佐藤靖之, 山本強, 土橋宜典  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.160  2012/10/20  [Not refereed][Not invited]
  • 古川歩, 土橋宜典, 山本強  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.128  2012/10/20  [Not refereed][Not invited]
  • 江頭一馬, 土橋宜典, 山本強  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.120  2012/10/20  [Not refereed][Not invited]
  • Yoshinori Dobashi  IPSJ SIG Notes  2012-  (10)  1  -1  2012/09/13  [Not refereed][Not invited]
     
    Almost fifty years have passed since the first system of computer graphics was developed. Recently, we see synthetic images created by using computer graphics techniques everywhere in our daily life. In this report, fundamental and application techniques of computer graphics are reviewed by tracing the history of computer graphics. The history of computer graphics can be classified into three stages: a founding period, a growth period, and a maturity period. In the founding period, most of the fundamental techniques were developed such as the hidden surface removal, basic intensity calculat...
  • XING Xiaoxiong, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  情報処理学会研究報告(CD−ROM)  2012-  (2)  ROMBUNNO.CG-147,NO.2  2012/08/15  [Not refereed][Not invited]
  • KUSUMOTO KATSUTOSHI, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI  情報処理学会研究報告(CD−ROM)  2012-  (2)  ROMBUNNO.CG-147,NO.6  2012/08/15  [Not refereed][Not invited]
  • 山上 晃平, 山本 強, 土橋 宜典  聴覚研究会資料  42-  (5)  459  -464  2012/07/19  [Not refereed][Not invited]
  • 古家亙, 岩崎慶, 土橋宜典, 西田友是  情報処理学会論文誌ジャーナル(CD-ROM)  53-  (7)  1905  -1914  2012/07/15  [Not refereed][Not invited]
  • 古家 亙, 岩崎 慶, 土橋 宜典, 西田友是  情報処理学会論文誌  53-  (7)  1905  -1914  2012/07/15  [Not refereed][Not invited]
     
    We propose a real-time rendering method for dynamic scenes under all-frequency environmental lighting. To render the object surfaces illuminated by environmental lighting, the product of the environmental lighting, the visibility function at each shading point on the object surfaces, and the BRDF is integrated. Our method represents the environmental lighting and the BRDFs with spherical Gaussians and represents the visibility functions with spherical signed distance functions (SSDFs). Although these representations enable us to render scenes under all-frequency lighting in real-time, the previous method is limited to static scenes since the computational costs of SSDFs are quite high. To address this problem, we propose an efficient calculation method of SSDFs by approximating the object geometries with a set of spheres. This makes it possible to render fully dynamic scenes where the viewpoints, lighting, and BRDFs can be changed at run-time and objects can move, rotate and be deformed in real-time.
  • YAMAKAMI KOHEI, YAMAMOTO TSUYOSHI, DOBASHI YOSHINORI  電子情報通信学会技術研究報告  112-  (125(EA2012 45-53))  41-46  -46  2012/07/12  [Not refereed][Not invited]
     
    Parametric loudspeaker is widely used for sending directional sounds in limited area. In this study, we propose the system with Multi-beam single sideband modulation technique to realize a directional beam using the smaller number of ultrasonic transducer. In this method, we can create a audible frequency sound area by multiplying the ultrasonic carrier sound area and carrier-suppressed SSB sound area. By employing proposed method, we generate a narrower directional beam with the smaller number of ultrasonic transducer than the conventional method. The usefulness of our loudspeaker system have been verified experimentally.
  • YUE Yonghao, 岩崎慶, CHEN Bing‐Yu, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2012-  ROMBUNNO.33  2012/06/23  [Not refereed][Not invited]
  • 石川知一, YUE Yonghao, 岩崎慶, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2012-  ROMBUNNO.23  2012/06/23  [Not refereed][Not invited]
  • 岩崎慶, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2012-  ROMBUNNO.13  2012/06/23  [Not refereed][Not invited]
  • 西野孝則, 岩崎慶, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD−ROM)  2012-  ROMBUNNO.7  2012/06/23  [Not refereed][Not invited]
  • Katsutoshi Kusumoto, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2012-  (6)  1  -6  2012/06/15  [Not refereed][Not invited]
     
    Display of clouds is one of the important factors in creating images of outdoor scenes by using computer graphics. In this paper we present a new method for controlling cumulus clouds like cotton. When simulating cumulus clouds, their shapes depend on many simulation parameters. It is difficult to adjust those parameters so that the clouds form desired shapes. Therefore, we propose a method that can control the cloud simulation in order to generate clouds of the shape specified by user. The user specifies the multiple shapes of the clouds at several key frames. By using our method, cumulus ...
  • DOBASHI Yoshinori  電子情報通信学会技術研究報告. SIS, スマートインフォメディアシステム  112-  (78)  57  -57  2012/06/07  
    Almost fifty years have passed since the first system of computer graphics was developed. Recently, we see synthetic images created by using computer graphics techniques everywhere in our daily life. In this report, fundamental and application techniques of computer graphics are reviewed by tracing the history of computer graphics. The history of computer graphics can be classified into three stages: a founding period, a growth period, and a maturity period. In the founding period, most of the fundamental techniques were developed such as the hidden surface removal, basic intensity calculation, display of shadows, and texture mapping. These techniques have been used continuously until today. Next, in the growth period, techniques that enable us to synthesize images with higher realism were developed such as the ray tracing. Methods developed in this period were not only for the realistic image synthesis. Various types of methods, such as illustrative rendering of 3D objects, were developed in order to extend the ability of computer graphics. Nowadays, the computer graphics research is in the period of maturity. Based on the methods developed in the founding and the growth periods, novel application techniques are actively developed. Thanks to the development of high performance computers, methods for displaying complicated and large-scale objects tend to be developed. A low-cost but high-performance parallel processing unit, called GPU, significantly accelerates this research trend. This report provides with a brief study of the past and the future of computer graphics by looking over the history of computer graphics,
  • 森田拓也, 佐藤周平, 土橋宜典, 山本強  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2012-  ROMBUNNO.5  2012/06  [Refereed][Not invited]
  • 土橋 宜典  情報処理  53-  (6)  562  -567  2012/05/15  
    コンピュータグラフィクス（CG）において，水，炎，雲などの自然現象を表現するための手法は数多く提案されている．それらの手法は，手続き的アプローチと物理ベースアプローチに大別できる．手続き的アプローチは少ない計算量でそれらしい映像を生成できる反面，リアリティの面で問題が残る．一方，物理ベースアプローチは計算コストは高いが，リアルな映像を作成できる．本項では，まずこれらのアプローチについて，その考え方と利点・欠点について概説する．そして，物理ベースアプローチに関して，特に注目が集まっている数値流体解析を利用したアプローチについて，基本的な考え方と最近の研究事例について解説する．
  • Fukumoto Kazuya, Okada Goro, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2012-  (2)  137  -137  2012/03/06  [Not refereed][Not invited]
  • Yamakami Kohei, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2012-  (0)  186  -186  2012/03/06  [Not refereed][Not invited]
  • Sato Yasuyuki, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2012-  (2)  135  -135  2012/03/06  [Not refereed][Not invited]
  • Okada Goro, Fukumoto Kazuya, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2012-  (2)  136  -136  2012/03/06  [Not refereed][Not invited]
  • YOSHIKAWA Takaho, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  PROCEEDINGS OF THE ITE WINTER ANNUAL CONVENTION  2012-  (0)  2  -1-1  2012  [Not refereed][Not invited]
     
    We propose an efficient method for calculating spherical signed distance function that has been used for the realistic rendering of virtual objects illuminated by environmental ligting. We accelerate the computation by hierarchically grouping vertices of the objects. Our method achieves 1.8 faster computation.
  • Wataru Iwasaki, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes. CVIM  2011-  (23)  1  -6  2011/11/10  [Not refereed][Not invited]
     
    In creating synthetic images of outdoor scenes using computer graphics, clouds play an important role in enhancing the realism of the synthetic images. Many methods have therefore been proposed for displaying clouds and a volumetric representation is often employed to render realistic clouds. However, the realism of the resulting images depends on many rendering parameters and it is often difficult to adjust those parameters manually to achieve sufficient realism. In order to address this problem, this paper proposes a method for estimating the rendering parameters for clouds from a single ...
  • Syuhei Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes. CVIM  2011-  (24)  1  -6  2011/11/10  [Not refereed][Not invited]
     
    In recent years, many methods have been proposed for simulating realistic motions of fluids such as water and fire. However, the computational cost for simulating fluid motion is very expensive. We propose a method using a precomputed database to solve this problem. Our method efficiently generates the desired animation of fire by linearly combining precomputed basic velocity fields stored in a database.
  • Wataru Iwasaki, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2011-  (23)  1  -6  2011/11/10  [Not refereed][Not invited]
     
    In creating synthetic images of outdoor scenes using computer graphics, clouds play an important role in enhancing the realism of the synthetic images. Many methods have therefore been proposed for displaying clouds and a volumetric representation is often employed to render realistic clouds. However, the realism of the resulting images depends on many rendering parameters and it is often difficult to adjust those parameters manually to achieve sufficient realism. In order to address this problem, this paper proposes a method for estimating the rendering parameters for clouds from a single ...
  • Syuhei Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2011-  (24)  1  -6  2011/11/10  [Not refereed][Not invited]
     
    In recent years, many methods have been proposed for simulating realistic motions of fluids such as water and fire. However, the computational cost for simulating fluid motion is very expensive. We propose a method using a precomputed database to solve this problem. Our method efficiently generates the desired animation of fire by linearly combining precomputed basic velocity fields stored in a database.
  • 佐藤周平, 土橋宜典, 山本強  電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM)  2011-  ROMBUNNO.18  2011/10/22  [Not refereed][Not invited]
  • 渋川雄平, 佐藤周平, 土橋宜典, 山本強  電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM)  2011-  ROMBUNNO.12  2011/10/22  [Not refereed][Not invited]
  • 森田拓也, 佐藤周平, 土橋宜典, 山本強  電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM)  2011-  ROMBUNNO.14  2011/10/22  [Not refereed][Not invited]
  • Syuhei Sato, Yoshinori Dobashit, Tsuyoshi Yamamoto, Ken Anjyo  Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers  65-  (10)  1446  -1451  2011/10  [Not refereed][Not invited]
     
    Recently, many methods for simulating natural phenomena on the basis of fluid simulation have been proposed. A method for simulating explosions was also proposed, but the shapes of the simulated explosions depend on many simulation parameters. Therefore, creating the desired shape for an explosion as specified by the user is difficult. In this paper, we propose a method for controlling explosion simulations in order to form the desired shapes. Our method optimizes the initial intensity distribution of an explosion and controls the simulation to minimize the difference between the target shape and the shape of the simulated explosion. We use a predictive approach to control the explosion simulation accurately. Using the proposed method, animations of explosions controlled into specified shapes can be generated.
  • Tomokazu Ishikawa, Yonghao Yue, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita  IPSJ SIG Notes  2011-  (7)  1  -8  2011/08/28  [Not refereed][Not invited]
     
    In this paper, we focus on magnetic fluids. Magnetic fluids behave as both fluids and as magnetic bodies, and these characteristics allow them to generate `spike-like' shapes along a magnetic field. Magnetic fluids are popular materials for use in works of art. Our goal is to simulate such works of art. It is known, however, that the spikes are difficult to simulate using fully physical-based methods. Therefore, we propose a visually plausible method that combines a procedural approach together with the SPH (smoothed particle hydrodynamics) method. We demonstrate that the spike shapes can b...
  • YUE Yonghao, 岩崎慶, CHEN Bing‐Yu, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2011-  RENDARINGU,YONGHAO YUE  2011/06/24  [Not refereed][Not invited]
  • 西野孝則, 岩崎慶, 土橋宜典  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2011-  ANIMESHON,NISHINOTAKANORI  2011/06/24  [Not refereed][Not invited]
  • 古家亙, 岩崎慶, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2011-  RENDARINGU,FURUYAWATARU  2011/06/24  [Not refereed][Not invited]
  • Hiroyuki Kubo, Yoshinori Dobashi, Jumpei Tsuda, Shigeo Morishima  IPSJ SIG Notes  2011-  (2)  1  -6  2011/06/20  [Not refereed][Not invited]
     
    Simulating sub-surface scattering is one of the most effective ways to realistically synthesize translucent materials, especiallyhuman skin. This paper describes a technique of Curvature-Dependent Reflectance Function (CDRF) as a real-time skin shader and its implementation for a practical usage. For a production pipeline, we build a simple workflow, and prepare a method for exaggeration of scattering effects to describe a character's skin individuality.
  • Hikaru Hatazawa, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2011-  (3)  1  -6  2011/06/20  [Not refereed][Not invited]
     
    Recently, computer graphics is widely used for synthesizing images of a virtual world, such as computer games, and the reality of the virtual world can be improved by adding the sound corresponding to the image. However, finding and recording an appropriate sound that matches to the images are often difficult and time-consuming tasks. In this paper, we propose a method for generating various sound effects from a single recorded sound by analyzing the sound wave. Our method can reduce the memory consumption for the sound wave compared to using multiple sound waves for generating sound variat...
  • Yuta Chiba, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2011-  (6)  1  -6  2011/06/20  [Not refereed][Not invited]
     
    Recently, in the field of computer graphics, simulating realistic motion of fluids based on computational fluid dynamics has been studied by many researchers. In addition to these researches, many methods for generating desired motions of fluids have also been developed. However, it is generally difficult to create the desire motion of fluids since the fluid simulation depends on many parameters. In this paper, we focus on the simulation of water and propose a method that enables us to create the desire motion of water by using a pre-computed simulation database.
  • Ryuichi Fukushi, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2011-  (7)  1  -6  2011/06/20  [Not refereed][Not invited]
     
    Computer graphics has become a useful tool for many applications such as computer-aided interior design systems. In this research, we propose an editing system for curtains that are an important element for the interior design. In our method, a physically-based cloth simulator is used to generate realistic shapes of curtains. However, such a simulator has many parameters and it is difficult to adjust those parameters to generate desired shapes of curtains. In addition, the computational cost for the simulation is too expensive for interactive operations. To address these problems, our metho...
  • 佐藤周平, 土橋宜典, 山本強  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2011-  ANIMESHON,SATOSHUHEI  2011/06  [Refereed][Not invited]
  • 西野孝則, 岩崎慶, 土橋宜典  情報処理学会全国大会講演論文集  73rd-  (4)  4.87-4.88  2011/03/02  [Not refereed][Not invited]
  • 西野孝則, 岩崎慶, 土橋宜典  全国大会講演論文集  2011-  (1)  87  -89  2011/03/02  [Not refereed][Not invited]
     
    屋外景観映像の作成において,写実的かつ動的な雲の表示は重要である.<br />しかし,写実的な雲を表示するには多重散乱光を考慮する必要があり,<br />毎フレームにおいて多重散乱光の輝度計算を行うのは非常に計算コストが<br />高い.そこで,任意の雲の密度分布をウェーブレット関数で表し,<br />ボクセル間の密度の積分値を前計算しておく.そして,前計算した<br />積分値と各ウェーブレット関数の重みとの累積をとることにより,<br />任意の雲のボクセル間の減衰率を非線形近似で表し,輝度計算を<br />高速化する手法を提案する.また,膨大な量の前計算データを圧縮し,<br />GPU上に格納することによりCUDAを用いたリアルタイムレンダリングを<br />実現した.
  • Sasamoto Ryosuke, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2011-  (2)  53  -53  2011/02/28  [Not refereed][Not invited]
  • Yokota Yasuto, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the IEICE General Conference  2011-  (2)  54  -54  2011/02/28  [Not refereed][Not invited]
  • MARUYA Miori, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  ITE Technical Report  35-  (9)  41  -45  2011/02/14  [Not refereed][Not invited]
     
    Increasing medical image data amount by improvement of technology, Computer-Aided Detection was developed. It is very popular method that computer detects lesion by using image procession, but it depends heavily on parameters such as region, modality and type of lesion. We are suggesting a method to detect important image that contains lesion without depending on image content. In our method, computer learns user's browsing history and evaluates important degree of each image. We also propose the medical image viewer that helps controlling medical image data with large amount.
  • MARUYA Miori, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  IEICE technical report  110-  (420)  41  -45  2011/02/14  [Not refereed][Not invited]
     
    Increasing medical image data amount by improvement of technology, Computer-Aided Detection was developed. It is very popular method that computer detects lesion by using image procession, but it depends heavily on parameters such as region, modality and type of lesion. We are suggesting a method to detect important image that contains lesion without depending on image content. In our method, computer learns user's browsing history and evaluates important degree of each image. We also propose the medical image viewer that helps controlling medical image data with large amount.
  • MARUYA Miori, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  IEICE technical report. Image engineering  110-  (421)  41  -45  2011/02/14  [Not refereed][Not invited]
     
    Increasing medical image data amount by improvement of technology, Computer-Aided Detection was developed. It is very popular method that computer detects lesion by using image procession, but it depends heavily on parameters such as region, modality and type of lesion. We are suggesting a method to detect important image that contains lesion without depending on image content. In our method, computer learns user's browsing history and evaluates important degree of each image. We also propose the medical image viewer that helps controlling medical image data with large amount.
  • 石川知一, YUE Yonghao, 岩崎慶, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2011-  2011
  • KUSUMOTO Katsutoshi, DOBASHI Yoshinori, YAMAMOTO Tsutyoshi  PROCEEDINGS OF THE ITE WINTER ANNUAL CONVENTION  2011-  (0)  5  -1-1  2011  [Not refereed][Not invited]
     
    In this paper, we present a new method for modeling cumulus clouds based on numerical simulation of cloud formation. Our method controls the simulation so that a desired distribution of clouds specifi ed by the user is generated.
  • Wataru Iwasaki, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2010-  (5)  1  -5  2010/11/01  [Not refereed][Not invited]
     
    In this research, we focus on the display of clouds represented by volume data. Generally, volume data can be visualized by a volume rendering technique. However, there are many parameters that have to be specified by the user and it is often difficult to create the desired image by adjusting those parameters. In this paper, we propose a system that allows the user to specify the parameters intuitively and to generate the desired results easily. In our system, the user does not directly specify the rendering parameters, but implicitly specify them by intuitive operations. By using our syste...
  • Ayumi Ono, Yoshinori Dobashi, Tsuyoshi Yamamoto  IPSJ SIG Notes  2010-  (7)  1  -6  2010/11/01  [Not refereed][Not invited]
     
    In this research, we focus on the sky that is an important element of outdoor scenes, and develop an intuitive editing system for sky image that can reflect the user's intension. Our method consists of two steps. The first step is a sky generation process, and the second step is a cloud synthesis process. In the first step, the intensity distribution and colors of the sky are created by using our intuitive user-interfaces. In the second step, we compose images of cloud extracted from photographs onto the sky created in the first step. However, the result might be look unnatural if the cloud...
  • Yonghao Yue, Kei Iwasaki, Bing-Yu Chen, Yoshinori Dobashi, Tomoyuki Nishita  IPSJ SIG Notes  2010-  (3)  1  -6  2010/11/01  [Not refereed][Not invited]
     
    Photo-realistic rendering of participating media with light scattering in consideration is important in computer graphics, and is typically computed using Monte Carlo based methods. The key technique in such methods is the free path sampling, which is used for determining the distance (free path) between successive scattering events. In our previous work, we proposed an unbiased and adaptive free path sampling method14),15) and the sampling efficiency was significantly improved over existing methods. The key concept of that method is to partition the spatial domain according to the spatial ...
  • 久保尋之, 土橋宜典, 森島繁生  日本顔学会誌  10-  (1)  111  2010/09/24  [Not refereed][Not invited]
  • 西野孝則, 岩崎慶, 土橋宜典  平成22年度情報処理学会関西支部支部大会講演論文集  2010-  (2010)  2010/09/22  [Not refereed][Not invited]
  • Sasamoto Ryosuke, Yamamoto Tsuyoshi, Dobashi Yoshinori  情報科学技術フォーラム講演論文集  9-  (3)  293  -294  2010/08/20  [Not refereed][Not invited]
  • Maruya Miori, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム講演論文集  9-  (2)  565  -566  2010/08/20  [Not refereed][Not invited]
  • Ono Ayumi, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム講演論文集  9-  (3)  237  -238  2010/08/20  [Not refereed][Not invited]
  • Sato Yasuyuki, Yamamoto Tsuyoshi, Dobashi Yoshinori  情報科学技術フォーラム講演論文集  9-  (3)  291  -292  2010/08/20  [Not refereed][Not invited]
  • Yokota Yasuto, Yamamoto Tsuyoshi, Dobashi Yoshinori  情報科学技術フォーラム講演論文集  9-  (3)  295  -296  2010/08/20  [Not refereed][Not invited]
  • Iwasaki Wataru, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム講演論文集  9-  (3)  317  -318  2010/08/20  [Not refereed][Not invited]
  • Shinzo Yusuke, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム講演論文集  9-  (3)  337  -338  2010/08/20  [Not refereed][Not invited]
  • 千葉 雄太, 土橋 宜典, 山本 強  研究会講演予稿  251-  17  -20  2010/07/23  [Not refereed][Not invited]
  • CHIBA Yuta, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  ITE Technical Report  34-  (31)  17  -20  2010/07/23  [Not refereed][Not invited]
     
    Recently, in the field of computer graphics, researches for simulating realistic motion of fluids based on computational fluid dynamics have been studied by many researchers. In addition to these researches, several methods to generate desired shapes by controlling the fluid simulation have also been developed. However, the fluid motion controlled by the previous methods often looks unnatural since unrealistic external forces are used to control the fluid simulation. In this paper, we focus on the simulation of water and propose a method that is able to control the motion of water to natura...
  • 久保尋之, 土橋宜典, 森島繁生  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2010-  MODERINGU,KUBOHIROYUKI  2010/06/26  [Not refereed][Not invited]
  • 内田英行, 岩崎慶, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2010-  RYUTAISHIMYURESHON,UCHIDAHIDEYUKI  2010/06/26  [Not refereed][Not invited]
  • YUE Yonghao, 岩崎慶, CHEN Bing‐Yu, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2010-  RENDARINGU,YONGHAO YUE  2010/06/26  [Not refereed][Not invited]
  • 西尾竜平, 岩崎慶, 土橋宜典  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2010-  RENDARINGU,NISHIORYUHEI  2010/06/26  [Not refereed][Not invited]
  • 新谷幹夫, 白石路雄, 土橋宜典, 岩崎慶, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2010-  RENDARINGU,SHIN'YAMIKIO  2010/06/26  [Not refereed][Not invited]
  • 佐藤周平, 土橋宜典, 山本強, 安生健一  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2010-  RYUTAISHIMYURESHON,SATOSHUHEI  2010/06  [Refereed][Not invited]
  • DOBASHI Yoshinori  The Journal of the Institute of Image Electronics Engineers of Japan  39-  (2)  215  -219  2010/03/25  [Not refereed][Not invited]
  • FUKUSHI Ryuichi, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  全国大会講演論文集  72-  (4)  "4  -49"-"4-50"  2010/03/08  [Not refereed][Not invited]
  • CHIBA Yuta, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  全国大会講演論文集  72-  (4)  "4  -315"-"4-316"  2010/03/08  [Not refereed][Not invited]
  • IWASAKI Wataru, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  全国大会講演論文集  72-  (4)  "4  -387"-"4-388"  2010/03/08  [Not refereed][Not invited]
  • Ikeda Kento, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2010-  (2)  210  -210  2010/03/02  [Not refereed][Not invited]
  • Ono Ayumi, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2010-  (2)  211  -211  2010/03/02  [Not refereed][Not invited]
  • 石川知一, YUE Yonghao, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2010-  2010
  • 佐藤周平, 土橋宜典, 山本強, 安生健一  情報処理学会研究報告(CD-ROM)  2009-  (4)  ROMBUNNO.CG-137,15  2009/12/15  [Not refereed][Not invited]
  • Syuhei Sato, Yoshinori Dobashi, Tsuyoshi Yamamoto, Kenichi Anjo  IPSJ SIG Notes  2009-  (15)  1  -6  2009/10/29  [Not refereed][Not invited]
     
    Recently, many simulation methods for natural phenomena based on fluids simulation have been proposed. A method for explosion is also proposed, but the shapes of the simulated explosions depend on many simulation parameters. Therefore, it is difficult to create a shape of explosion that users specified. In this paper, we propose a method for controlling explosion simulations to form shapes that users specified. The user specifies the multiple shapes of the explosion at several key frames. Using the proposed method, the animation of explosions controlled into specified shapes can be generated.
  • 土橋 宜典  研究会講演予稿  246-  (0)  29  -32  2009/10/23  [Not refereed][Not invited]
  • 佐藤周平, 土橋宜典, 山本強  電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM)  2009-  ROMBUNNO.184  2009/10/17  [Not refereed][Not invited]
  • SHINZO Yusuke, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  Technical report of IEICE. PRMU  109-  (249)  49  -54  2009/10/15  [Not refereed][Not invited]
     
    In this paper, we propose a method for estimating optical properties from a photograph and creating 2D cloud textures. Our method enables the user to change the shading of the generated clouds textures. There are some methods that can extract an image of foreground objects from a photograph and composite it into a different photograph. However, when applying those methods to clouds, unnatural images are often created, especially when the sun directions are different. We address this problem by estimating an attenuation coefficient and an albedo coefficient. Our method allows the user to cha...
  • 西尾竜平, 岩崎慶, 土橋宜典  平成21年度情報処理学会関西支部支部大会講演論文集  2009-  (2009)  2009/09/29  [Not refereed][Not invited]
  • ISHIKAWA Tomokazu, YUE Yonghao, DOBASHI Yoshinori, NISHITA Tomoyuki  情報処理学会研究報告. グラフィクスとCAD研究会報告  136-  (0)  E1  -E6  2009/08/20  [Not refereed][Not invited]
     
    コンピュータグラフィクス （CG） による天体現象の可視化は映画やゲームなどで需要がある。CG 分野においては，これまで木星や地球の画像生成に関する研究が成されてきたが，太陽を扱う手法は開発されていない。本研究では太陽の現象のうち，プロミネンスに着目する。プロミネンスは太陽表面に磁束管が浮上し，表面の流体を押し上げることで観測される。本稿では，磁気流体力学の基礎方程式を用いた効率的なシミュレーション方法について提案する。Visualization of astronomical phenomena using computer graphics (CG) is needed for movies and games. In the field of CG, though methods for rendering the Jupiter and the Earth from space were developed, little methods have been developed for visual simulation of the Sun. Among the phenomena related to the Sun, our research goal is the visual simulation of the solar prominence, which is observed when the fluid on the Sun's surface is raised by the flux tube. In this paper, we propose an efficient and physically-based method based on the basic equations of magnetohydrodynamics.
  • 岩崎慶, 土橋宜典, 西田友是  情報処理学会論文誌ジャーナル(CD-ROM)  50-  (8)  1917  -1925  2009/08/15  [Not refereed][Not invited]
  • 岩崎 慶, 土橋 宜典, 西田友是  情報処理学会論文誌  50-  (8)  1917  -1925  2009/08/15  [Not refereed][Not invited]
     
    This paper presents a BRDF modeling method, based on an inverse problem approach. Our method calculates BRDFs to match the appearance of the object specified by the user. By representing BRDFs by a linear combination of basis functions, outgoing radiances of the object surface can be represented using basis functions. The calculation of the desired BRDF results from calculating the corresponding coefficients of basis functions that minimize the sum of differences between the outgoing radiances, represented using basis functions and user specified radiances. The properties that BRDFs must satisfy are described by linear constraint conditions. This minimization problem can be solved, interactively, using a linearly constrained least squares approach. Thus, our method allows the user to design BRDFs directly, under fixed complex lighting and viewpoint, and to view the rendering results interactively, under dynamic lighting and viewpoint.
  • 新谷幹夫, 土橋宜典, 白石路雄, 岩崎慶, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2009-  ROMBUNNO.18  2009/06/25  [Not refereed][Not invited]
  • 岩崎慶, 宮前雄生, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2009-  ROMBUNNO.48  2009/06/25  [Not refereed][Not invited]
  • YUE Yonghao, 岩崎慶, CHEN Bing‐Yu, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2009-  ROMBUNNO.01  2009/06/25  [Not refereed][Not invited]
  • 佐藤周平, 土橋宜典, 山本強, 安生健一  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2009-  ROMBUNNO.03  2009/06  [Refereed][Not invited]
  • Shinzo Yusuke, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2009-  (2)  40  -40  2009/03/04  [Not refereed][Not invited]
  • Hama Daisuke, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2009-  (2)  42  -42  2009/03/04  [Not refereed][Not invited]
  • Sato Syuhei, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2009-  (2)  41  -41  2009/03/04  [Not refereed][Not invited]
  • Siren Batu, Yoshinori Dobashi, Tsuyoshi Yamamoto  Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers  63-  (10)  1453  -1458  2009  [Not refereed][Not invited]
     
    We propose a new, simple, and effective image-based rendering technique for synthesizing images of novel views from an image cluster, a large volume of precaptured images randomly distributed in a bounded region with known camera positions and orientations. Unlike methods that are based on sampling, and constructing and resampling the plenoptic function, our method uses a select and warp approach. We use scene depth information as additional input to render novel views from an image cluster that has fewer images than that used in plenoptic function based approaches. Furthermore, unlike the view interpolation approach that typically uses a small number of input images our method deals with large number, typically from several hundred to several thousand. Our method involves finding the optimal pixel from the input image cluster on the assumption that as the image is dense enough and as each pixel needed is visible from at least one of the input images, no occlusion occurs.
  • KUSUMOTO KATSUTOSHI, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI  IPSJ SIG Notes  2008-  (109)  61  -66  2008/10/31  [Not refereed][Not invited]
     
    Controlling the simulation of natural phenomena such as fire, smoke, water so that it forms desired shape is challenging problem in computer graphics, and many methods have been proposed. In this paper we present a new method for controlling sell-like clouds. The shapes of cell-like clouds depend on many simulation parameters to simulate them. It is difficult to adjust those parameters so that the clouds form desired shape. Therefore, we control the cloud simulation in order to generate clouds of the distribution specified by user. Our method can generate cell-like clouds with desired shape...
  • Yamada Daisuke, Yamamoto Tsuyoshi, Dobashi Yoshinori  ITE Technical Report  32-  (46)  11  -14  2008/10/23  [Not refereed][Not invited]
     
    In movies or computer game, realistic rendering of animals by 3DCG has been realized. For the rendering of an animal, a fur is one of the important factors and it is indispensable to create realistic images. However, in general, rendering of fur is computationally expensive, and global illumination effects have note been taken into account in the traditional methods. The goal of our research is the real-time rendering of the fur taking into account the global illumination effects. Our method utilizes the precomputed radiance transfer (PRT) method. That is, our method calculates the luminanc...
  • FUJII Yosuke, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  ITE Technical Report  32-  (46)  15  -18  2008/10/23  [Not refereed][Not invited]
     
    Deformation of 3D model in character animation is one of the important research fields in computer graphics. For the deformation of 3D models, a method using convergence calculation to generate desired shape is often employed. However, if shape is complex, convergence calculation would be very time-consuming. In general, it is genrally difficult to create rough and approximate control mesh that can realize the deformation efficiently with numerical stabilities. When a control mesh is too rough, the deformed shape would be very unnatural. When the control mesh was too fine, the computational...
  • Batu Siren, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム講演論文集  7-  (3)  195  -196  2008/08/20  [Not refereed][Not invited]
  • Fujii Yosuke, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム講演論文集  7-  (3)  221  -222  2008/08/20  [Not refereed][Not invited]
  • Kusumoto Katsutoshi, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム講演論文集  7-  (3)  223  -224  2008/08/20  [Not refereed][Not invited]
  • Hama Daisuke, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム講演論文集  7-  (3)  225  -226  2008/08/20  [Not refereed][Not invited]
  • Yamada Daisuke, Yamamoto Tsuyoshi, Dobashi Yoshinori  情報科学技術フォーラム講演論文集  7-  (3)  261  -262  2008/08/20  [Not refereed][Not invited]
  • Kuroda Yusuke, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム講演論文集  7-  (3)  265  -266  2008/08/20  [Not refereed][Not invited]
  • Eguchi Yukihisa, Dobashi Yoshinori, Yamamoto Tuyoshi  情報科学技術フォーラム講演論文集  7-  (3)  263  -264  2008/08/20  [Not refereed][Not invited]
  • 新谷幹夫, 白石路雄, 土橋宜典, 岩崎慶, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2008-  ROMBUNNO.1  2008/06/21  [Not refereed][Not invited]
  • YUE Yonghao, 岩崎慶, 土橋宜典, 西田友是  Visual Computing/グラフィクスとCAD合同シンポジウム予稿集(CD-ROM)  2008-  ROMBUNNO.4  2008/06/21  [Not refereed][Not invited]
  • Iizuka Taro, Yue Yonehao, Dobashi Yoshinori, Nishita Tomoyuki  全国大会講演論文集  70-  (2)  "2  -405"-"2-406"  2008/03/13  [Not refereed][Not invited]
  • Hama Daisuke, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2008-  (2)  102  -102  2008/03/05  [Not refereed][Not invited]
  • KURODA Yusuke, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  Reports of the Technical Conference of the Institute of Image Electronics Engineers of Japan  8-  (0)  17  -21  2008  [Not refereed][Not invited]
     
    Recently, many researchers have focused on the technique called non-photorealistic rendering. By using the technique, images that are similar to hand-drawn pictures can be generated automatically. Especially, methods for creating cartoon style pictures are often utilized since the methods can significantly reduce the word load required in the traditional manual animation production process. In this research, we propose an interactive method for cartoon rendering of smoke. In our system, the motions and densities of the smoke are calculated by using the computational fluid dynamics. For the cartoon rendering of the smoke, particles are generated in the flow. For each particle, the user can attach an arbitrary density distribution to determine the small-scale details of the smoke shape. This makes it possible to generate smoke with the desired details. The small-scale details can be interactively edited by a sketch-based user interface.
  • KUSUMOTO KATSUTOSHI, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI  IPSJ SIG Notes  2007-  (111)  7  -12  2007/11/12  [Not refereed][Not invited]
     
    Display of clouds is one of the important factors in creating images of outdoor scenes by using computer graphics. Methods based on fluid simulation are often used since they can simulate realistic movement and shape of clouds. However, the shape and movement of the simulated clouds depend on initial values of the parameters used in the cloud simulation. Therefore, it is difficult to create shape and movement of clouds that users intend. In this paper, we propose a method for generating clouds with shapes that users specified. By using our method, the cumulonimbus with desired shapes can be...
  • SHINYA MIKIO, SHIRAISHI MICHIO, DOBASHI YOSHINORI, IWASAKI KEI, NISHITA TOMOYUKI  IPSJ SIG Notes  2007-  (111)  31  -36  2007/11/12  [Not refereed][Not invited]
     
    Kubelka-Munk theory analatically calculates reflectance and transparensy of scattering materials and is widely used in non-photo-realistic rendering. However, it does not prvide BRDF (Bidirectional Reflectance Distribution Function) and has been hard to be applied to photo-realistic rendeiring. This paper generalizes the theory and derives a quasi-analytic fomulae providing BRDFs of scattering layered uniform materials. The volume rendering equation is applied to a layered surface and analytically solved by using the eigen-value analysis. It also presents theories to concatenating multiple ...
  • 金子 剛介, 土橋 宜典, 山本 強  ITE technical report  31-  (47)  77  -80  2007/10  [Not refereed][Not invited]
  • 小林 敏泰, 土橋 宜典, 山本 強  ITE technical report  31-  (47)  81  -84  2007/10  [Not refereed][Not invited]
  • DOBASHI Yoshinori, ANJYO Ken-ichi, YAMAMOTO Tsuyoshi  IPSJ SIG Notes  2007-  (84)  41  -46  2007/08/16  [Not refereed][Not invited]
     
    Recently, non-photorealistic rendering (NPR) techniques developed in the field of computer graphics (CG) have been widely used in many animation production systems. One of the reasons for this is that NPR techniques combined with 3DCG make it easier to produce images that are hardly created by hand. In this paper, we propose a system for modeling and rendering cartoon smoke animations. The proposed system allows the user to model the overall shapes and motions of the smoke interactively. Based on the specified shapes and motions, the system renders the cartoon smoke in real-time by combinin...
  • PHAM THUY, THI THU, YUE YONGHAO, DOBASHI YOSHINORI, NISHITA TOMOYUKI  IPSJ SIG Notes  2007-  (84)  59  -64  2007/08/16  [Not refereed][Not invited]
     
    Fluid simulation has become an important topic in the field of computer graphics. The aim of this paper is the realistic simulation of water waves caused by the interaction between water and air flows (i.e wind). In order to calculate water waves accurately, high resolution grids are required. However this leads to increasing computational cost. To overcome this problem, we present a new method for simulating water waves due to wind by using overlapping grids with different resolutions. The method makes it possible to generate accurate shapes of water waves without increasing computational ...
  • YUE Yonghao, 岩崎慶, 土橋宜典, 西田友是  Visual Computing グラフィクスとCAD合同シンポジウム予稿集  2007-  51  -56  2007/06/23  [Not refereed][Not invited]
  • 新谷幹夫, 白石路雄, 土橋宜典, 岩崎慶, 西田友是  Visual Computing グラフィクスとCAD合同シンポジウム予稿集  2007-  119  -124  2007/06/23  [Not refereed][Not invited]
  • Kusumoto Katsutoshi, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2007-  (2)  166  -166  2007/03/07  [Not refereed][Not invited]
  • KOBAYASHI Toshiyasu, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  Proceedings of the Annual Conference of the Institute of Image Electronics Engineers of Japan  35-  (0)  73  -74  2007  [Not refereed][Not invited]
     
    In recent years computer graphics have been used in many applications such as movies and computer games and the visual simulation of natural phenomena has become an important research topic. Especially, many researchers have paid attentions to the simulation of the natural phenomena related to fluids such as water, smoke and flame. In the traditional methods, a single grid was used for computing the fluid motion. However, it is necessary to increase the number of grid points in order to increase the accuracy, and this results in the high computational cost. The computational cost is further increased when objects with complicated shapes interact with the fluids. To address this problem, a method using overlapping grids has been proposed. In this paper, we propose a new method for the visual simulation of the water using the overlapping grids. Our method is very efficient and suitable for simulating the interaction of objects and water.
  • YOSHIDA Yuki, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  情報処理学会研究報告. CG,グラフィクスとCAD研究会報告  125-  (0)  101  -106  2006/11/16  [Not refereed][Not invited]
  • YOSHIDA Yuki, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  IPSJ SIG Notes  2006-  (119)  101  -106  2006/11/16  [Not refereed][Not invited]
     
    One of the important factors for creating synthetic images of a rainy scene by using computer graphics is raindrop streaks. Previously, the raindrop streaks are rendered by using a particle system. That is, raindrops are represented by particles and the raindrop streaks are rendered by drawing streaks of the particles. However, the number of the raindrops is about 100,000 in general. Therefore, rendering the streaks of all particles is computationally very expensive. This indicates that the rendering of the rainy scene in real-time is difficult by using the previous approach. To address thi...
  • IWASAKI KEI, DOBASHI YOSHINORI, YOSHIMOTO FUJIICHI, NISHITA TOMOYUKI  情報処理学会研究報告. CG,グラフィクスとCAD研究会報告  125-  (0)  113  -118  2006/11/16  [Not refereed][Not invited]
  • IWASAKI KEI, DOBASHI YOSHINORI, YOSHIMOTO FUJIICHI, NISHITA TOMOYUKI  IPSJ SIG Notes  2006-  (119)  113  -118  2006/11/16  [Not refereed][Not invited]
     
    Realistic image synthesis is one of the most important research subjects in Computer Graphics. This paper presents a fast rendering method for dynamic scenes, where objects arid light sources move, taking into accout interreflection. Our method calculates glossy interreflections of light by decomposing glossy BRDFs into incident direction dependent functions and outgoing direction dependent functions. Our method calculates the interreflected light illuminated by an object, by considering the object as a secondary light source. We represent the illumination distribution of the object surface...
  • KOSHIMURA Naoto, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  ITE technical report  30-  (55)  17  -20  2006/10/30  [Not refereed][Not invited]
  • DOBASHI Yoshinori, ENJYO Yoshihiro, YAMAMOTO Tsuyoshi  ITE technical report  30-  (55)  21  -24  2006/10/30  [Not refereed][Not invited]
  • SAKAI Masahiro, ITO Kazuhiko, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  ITE technical report  30-  (55)  103  -106  2006/10/30  [Not refereed][Not invited]
  • Yoshida Yuko, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム一般講演論文集  5-  (3)  199  -200  2006/08/21  [Not refereed][Not invited]
  • Enjyo Yoshihiro, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム一般講演論文集  5-  (3)  201  -202  2006/08/21  [Not refereed][Not invited]
  • Ishida Katsunori, Yamamoto Tsuyoshi, Dobashi Yoshinori  情報科学技術フォーラム一般講演論文集  5-  (3)  283  -284  2006/08/21  [Not refereed][Not invited]
  • 岩崎慶, 土橋宜典, 田村尚希, JOHAN Henry, 吉本富士市, 西田友是  Visual Computing グラフィクスとCAD合同シンポジウム予稿集  2006-  23  -28  2006/06/22  [Not refereed][Not invited]
  • Kuroda Yusuke, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2006-  (2)  87  -87  2006/03/08  [Not refereed][Not invited]
  • YAMAMOTO Tsuyoshi, DOBASHI Yoshinori  計測と制御 = Journal of the Society of Instrument and Control Engineers  45-  (1)  8  -12  2006/01/10  [Not refereed][Not invited]
  • IWASAKI KEI, MORO YOSHITAKA, DOBASHI YOSHINORI, NISHITA TOMOYUKI  IPSJ SIG Notes  2005-  (116)  121  -126  2005/11/18  [Not refereed][Not invited]
     
    In recent years, attention has been paid to particle-based fluid simulation, which represents fluids as a set of particles and simulates the fluids dynamics by the interactions between the particles. Several methods have been developed to simulate fluids by using particles in the field of Computer Graphics. Particle-based fluid simulation is easy to handle the deformations in the convection terms, but the computational cost is expensive since it requires the computation of the interactions between many neighbour particles. In recent years, GPU(Graphics Processor Unit) has made significant p...
  • 小野 佳織, 岩崎 慶, 土橋 宜典  研究会講演予稿  222-  (0)  57  -64  2005/11/18  [Not refereed][Not invited]
  • 岩崎慶, 吉本富士市, 土橋宜典, 西田友是  Visual Computing グラフィクスとCAD合同シンポジウム予稿集  2005-  117  -122  2005/06/16  [Not refereed][Not invited]
  • Suzuki Junji, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2005-  (2)  290  -290  2005/03/07  [Not refereed][Not invited]
  • Sato Tomoya, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2005-  (2)  292  -292  2005/03/07  [Not refereed][Not invited]
  • Yamada Yuki, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2005-  (2)  293  -293  2005/03/07  [Not refereed][Not invited]
  • SUZUKI JUNJI, SATO TOMOYA, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI  IPSJ SIG Notes  2005-  (13)  49  -54  2005/02/07  [Not refereed][Not invited]
     
    Recently, many researchers have paid attention to a technique called non-photorealistic rendering (NPR). In this paper as one of the NPR techniques, we propose a method for painterly rendering of water surface. We propose an efficient method for generating painterly images of water surface by making use of techniques used in the field of three-dimensional computer graphics. Our method can create not only static images but also painterly animations of water such as the river. Moreover, we develop an interactive system using our method. This enables the user to reflect the user's mind on the ...
  • YAMADA YUKI, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI  IPSJ SIG Notes  2004-  (121)  109  -114  2004/11/26  [Not refereed][Not invited]
     
    Recently, realistic image synthesis using computer graphics has been used in various fields. The reality of the synthetic images can be improved by taking into account specular reflections such as mirrors, sufaces of cars, glass windows of buildings reflecting other objects. So, there are many methods to simulate the specular reflections. However, the simulation of this phenomenon is quite complex and therefore is very time-consuming. This is especially true for glossy specular reflections. On the other hand, the recent advancement of graphics hardware has made significant progress in the p...
  • BATO Siren, AOYAMA Yuki, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  IEICE technical report.  104-  (430)  37  -42  2004/11/09  [Not refereed][Not invited]
     
    Many works has been done to explore how to reproduce computer graphics in the real world. One of these approaches is using projectors to graphically animate physical objects in the real word. In this paper we describe a new approach to graphically reproduce the original medical object by projecting texture onto the surface of the physical model made from multi-slice medical data using 3D printer. Proposed system consists of real-time position recognition of target object and dynamic texture projection onto the object. This system aims to put virtual coloring and/or annotative information on...
  • HOSHINO TAKASHI, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI  IPSJ SIG Notes  2004-  (86)  35  -40  2004/08/18  [Not refereed][Not invited]
     
    Recently, computer graphics have been used in various fields. Especially, a technique for rendering cartoon images, expressed by the eel-shading and the outline, is expected to animation productions. In this paper, we propose a method for creating cartoon images and animation of smoke. In the method, images are created by using volume data representing smoke. The proposed method makes it possible to create cartoon images of dynamic smoke viewed from arbitrary viewpoints in real time.
  • 石川 知一, 土橋 宜典, 宮崎 玲  研究会講演予稿  210-  (0)  11  -16  2004/05/21  [Not refereed][Not invited]
  • 石川 知一, 土橋 宜典, 宮崎 玲, 西田 友是  第66回全国大会講演論文集  2004-  (1)  209  -210  2004/03/09  [Not refereed][Not invited]
  • 柳田哲一, 岩崎慶, 土橋宜典, 西田友是  情報処理学会全国大会講演論文集  66th-  (4)  4.181-4.182  2004/03/09  [Not refereed][Not invited]
  • 柳田 哲一, 岩崎 慶, 土橋 宜典, 西田 友是  第66回全国大会講演論文集  2004-  (1)  179  -180  2004/03/09  [Not refereed][Not invited]
  • Sato Tomoya, Dobashi Yoshinori, Yamamoto Tsuyoshi, Takao Katsumi, Anjyo Kenichi  Proceedings of the IEICE General Conference  2004-  (2)  328  -328  2004/03/08  [Not refereed][Not invited]
  • HOSHINO TAKASHI, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI  IPSJ SIG Notes  2004-  (16)  43  -47  2004/02/12  [Not refereed][Not invited]
     
    Recently, computer graphics have been used in various fields. Especially, a technique called non-photorealistic rendering (NPR) has become indispensable for cartoon movies, art, and so on. In these fields, NPR is used for simulating brush strokes/patterns to create painterly images. In this paper, we propose a method for painterly animation of clouds. In the method, images are created by using volume data representing clouds. The proposed method makes it possible to create painterly images of dynamic clouds viewed from arbitrary viewpoints.
  • SATO TOMOYA, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI, TAKAO KATSUMI, ANJYO KEN  IPSJ SIG Notes  2004-  (16)  49  -54  2004/02/12  [Not refereed][Not invited]
     
    In the cel animation workplace, non-photorealistic rendering (NPR) techniques are often applied to a 3D scene model, which is constructed by referring to the 2D hand-drawn images of the scene. There exist a lot of scene features that must be modeled from the 2D information. The accentuation effects are amongst the most important features in a hand-drawn scene. In this context, accentuation refers to adding hand-drawn shading of the scene. The specific region that an artist wishes the viewer to observe is drawn brighter than the other regions. In this paper, a method is proposed for the extr...
  • 岩崎慶, 土橋宜典, 西田友是  Visual Computing グラフィクスとCAD合同シンポジウム予稿集  2003-  207  -212  2003/06/19  [Not refereed][Not invited]
  • 柳田哲一, 岩崎慶, 土橋宜典, 西田友是  情報処理学会全国大会講演論文集  65th-  (4)  4.109-4.110  2003/03/25  [Not refereed][Not invited]
  • 柳田 哲一, 岩崎 慶, 土橋 宜典, 西田 友是  第65回全国大会講演論文集  2003-  (1)  109  -110  2003/03/25  [Not refereed][Not invited]
  • TAKADA SHINTARO, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI  IPSJ SIG Notes  2003-  (15)  67  -72  2003/02/14  [Not refereed][Not invited]
     
    To create realistic townscape images, the skylight as well as the sunlight have to be taken into account to compute illuminance of objects. But it is extremely expensive to calculate illuminance by the skylight. We propose a fast method for rendering townscape images taking into account the skylight, illuminance. In the proposed method, the rendering of images is accelerated by graphics hardware, and the calculation cost is reduced by using the idea of LOD (Level of Detail). The proposed method is efficient especially for rendering mass polygon data such as townscape. Furthermore, We extend our method to making animations.
  • KUMAZAWA SEIJI, DOBASHI YOSHINORI, YAMAMOTO TSUYOSHI  IPSJ SIG Notes  2003-  (15)  87  -92  2003/02/14  [Not refereed][Not invited]
     
    Many automatie region extraction methods for medical images, which aim at the computer-assisted diagnosis, have been proposed. Doctors correct the results of automatic extraction manually since these results are imperfect, in most cases. Because this manual correction is a very time consuming task, it is necessary to develop the system which supports this correction. In this paper, we propose a region extraction method which can correct the results of automatic extraction interactively. The automatic extraciton in our method is based on both morphological operation and region growing method...
  • YOSHIKAWA Shigeki, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  ITE Technical Report  27-  (8)  5  -10  2003/02/03  [Not refereed][Not invited]
     
    In this research, using a 3D digitizer as an interface, we propose a system which can create clouds intuitively by carrying out direct pointing in the 3D space. It makes possible to create the desired clouds interactively in the position where a user wants. Various methods have been developed for modeling clouds to create realistic images of clouds. However they have problems, that is, like that calculation cost is expensive or a parameter setup is complicated. In this system, it is possible for a user to create clouds easily without spending calculation time.
  • YOSHIKAWA Shigeki, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  電子情報通信学会技術研究報告. ITS  102-  (629)  5  -10  2003/01/27  [Not refereed][Not invited]
     
    In this research, using a 3D digitizer as an interface, we propose a system which can create clouds intuitively by carrying out direct pointing in the 3D space. It makes possible to create the desired clouds interactively in the position where a user wants. Various methods have been developed for modeling clouds to create realistic images of clouds. However they have problems, that is, like that calculation cost is expensive or a parameter setup is complicated. In this system, it is possible for a user to create clouds easily without spending calculation time.
  • YOSHIKAWA Shigeki, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  IEICE technical report. Image engineering  102-  (631)  5  -10  2003/01/27  [Not refereed][Not invited]
     
    In this research, using a 3D digitizer as an interface, we propose a system which can create clouds intuitively by carrying out direct pointing in the 3D space. It makes possible to create the desired clouds interactively in the position where a user wants. Various methods have been developed for modeling clouds to create realistic images of clouds. However they have problems, that is, like that calculation cost is expensive or a parameter setup is complicated. In this system, it is possible for a user to create clouds easily without spending calculation time.
  • Iwasaki Kei, Dobashi Yoshinori, Nishita Tomoyuki  IPSJ SIG Notes  2002-  (109)  41  -46  2002/11/22  [Not refereed][Not invited]
     
    Caustics pattern is the light effect caused by the divergence and convergence of the light. Several methods have been developed to render caustics. However calculating caustics is quite complex and therefore it is time consuming. Recently. graphics hardware has made significant progress in the performance. This fact encourages researchers to research the acceleration of realistic image synthesis. We present a fast method for rendering caustics on objects within water by using graphics hardware. To render objects within water viewed from above the water surface, caustics on objects and refra...
  • Kumazawa Seiji, Yamamoto Tsuyoshi, Dobashi Yoshinori  情報技術レターズ  1-  (0)  123  -124  2002/09/13  [Not refereed][Not invited]
  • Takada Shintaro, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報技術レターズ  1-  (0)  165  -166  2002/09/13  [Not refereed][Not invited]
  • Yamada Fumihiro, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム一般講演論文集  2002-  (3)  219  -220  2002/09/13  [Not refereed][Not invited]
  • Sato Tomoya, Dobashi Yoshinori, Yamamoto Tsuyoshi  情報科学技術フォーラム一般講演論文集  2002-  (3)  231  -232  2002/09/13  [Not refereed][Not invited]
  • Dobashi Yoshinori, Yamamoto Tsuyoshi, Nishita Tomoyuki  情報技術レターズ  1-  (0)  167  -168  2002/09/13  [Not refereed][Not invited]
  • Mizuno Ryoichi, Dobashi Yoshinori, Nishita Tomoyuki  IPSJ SIG Notes  2002-  (77)  115  -120  2002/08/08  [Not refereed][Not invited]
     
    The animation of the volcanic smoke is useful for natural disaster simulations, entertainments, etc. In this paper, we propose a model to generate realistic animations of the volcanic smoke. The model is designed by taking the variety of the atmospheric density along the height and the loss of the pyroclasts (fragments of magma). Thus, the model is based on the dynamics of the volcanic smoke. Moreover, we solve the Navier-Stokes equations of the model by using the Coupled Map Lattice (CMIL) that is an efficient solver. Hence, in our system, the behavior of the volcanic smoke can be calculat...
  • KUMAZAWA Seiji, YAMAMOTO Tsuyoshi, DOBASHI Yoshinori  IEICE technical report.  102-  (223)  7  -12  2002/07/12  [Not refereed][Not invited]
     
    In functional magnetic resonance imaging (fMRI), one serious problem is that these images depict false activation areas resulting from image-to-image physiological movements of subject during fMRI data acquisition. In order to truly detect functional activation areas, it is necessary to eliminate the effects of physiological movements of subject (i.e., gross head motion, pulsation and respiration) from fMRI time series data. In this paper, we propose a method for eliminating false activation due to physiological movements of subject. The proposed method estimates subject movements by using ...
  • Miyazaki Ryo, Dobashi Yoshinori, Nishita Tomoyuki  IPSJ SIG Notes  2002-  (33)  43  -48  2002/04/19  [Not refereed][Not invited]
     
    Simulation of the natural phenomenon is one of the important research fields in computer graphics. In particular, clouds play an important role in creating images of outdoor scenes. The fluid simulation is effective to create realistic clouds because clouds are visualization of atmospheric fluid. In this paper, we propose simulation technique based on numerical solution of the partial differential equation of the atmospheric fluid model for creating the animation of cumulus and cumulonimbus with feature form by turbulent vortex.
  • 岩崎 慶, 西田 友是, 土橋 宜典  第64回全国大会講演論文集  2002-  (1)  45  -46  2002/03/12  [Not refereed][Not invited]
  • YAMADA Fumihiro, DOBASHI Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2002-  (2)  2002/03/07  [Not refereed][Not invited]
  • Sato Tomoya, Dobasi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2002-  (2)  2002/03/07  [Not refereed][Not invited]
  • S Kumazawa, T Yamamoto, Y Dobashi  IEICE TRANSACTIONS ON INFORMATION AND SYSTEMS  E85D-  (1)  60  -68  2002/01  [Not refereed][Not invited]
     
    In functional brain images obtained by analyzing higher human brain functions using functional magnetic resonance imaging (fMRI), one serious problem is that these images depict false activation areas (artifacts) resulting from image-to-image physiological movements of subject during fMRI data acquisition. In order to truly detect functional activation areas, it is necessary to eliminate the effects of physiological movements of subject (i.e., gross head motion, pulsatile blood and cerebrospinal fluid (CSF) flow) from fMRI time series data. In this paper, we propose a method for eliminating artifacts due to not only rigid-body motion such as gross head motion, but also non-rigid-body motion like the deformation caused by the pulsatile blood and CSF flow. The proposed method estimates subject movements by using gradient methods which can detect subpixel optical flow. Our method estimates the subject movements on a "pixel-by-pixel" basis, and achieves the accurate estimation of both rigid-body and non-rigid-body motion. The artifacts are reduced by correction based on the estimated movements. Therefore, brain activation areas are accurately detected in functional brain images. We demonstrate that our method is valid by applying it to real fMRI data and that it can improve the detection of brain activation areas.
  • Iwasaki Kei, Dobashi Yoshinori, Nishita Tomoyuki  IPSJ Magazine  42-  (9)  41  -44  2001/09/15  [Not refereed][Not invited]
  • DOBASHI Yoshinori  The Journal of the Institute of Electronics, Information, and Communication Engineers  84-  (9)  673  -675  2001/09/01  [Not refereed][Not invited]
  • YAMADA Fumihiro, DOBASHI Yoshinori, YAMAMOTO Tsuyoshi  Proceedings of the Society Conference of IEICE  2001-  (0)  203  -203  2001/08/29  [Not refereed][Not invited]
  • Satou Tomoya, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the Society Conference of IEICE  2001-  (0)  204  -204  2001/08/29  [Not refereed][Not invited]
  • Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the Society Conference of IEICE  2001-  (0)  205  -205  2001/08/29  [Not refereed][Not invited]
  • Kumazawa Seiji, Yamamoto Tsuyoshi, Dobashi Yoshinori  Proceedings of the Society Conference of IEICE  2001-  (0)  277  -277  2001/08/29  [Not refereed][Not invited]
  • DOBASHI Yoshinori, NISHINOTO Nobuo, KANEDA Kazufumi, YAMASHITA Hideo  The Journal of the Institute of Image Electronics Engineers of Japan  30-  (4)  362  -370  2001/07/25  [Not refereed][Not invited]
     
    Recently many researchers have been trying to display natural phenomena such as clouds, ocean waves, and flames using computer graphics. This paper proposes a fast method for generating images of clouds. Since clouds consist of particles with a high albedo, multiple scattering cannot be ignored. In our method, the density distribution of clouds is expressed by sets of metaballs. A metaball is a sphere and a density distribution is defined inside it. Multiple scattering is taken into account by computing the energy transfer between metaballs. To reduce the computation time, metaballs are grouped into a hierarchical structure, and graphics hardware is utilized. The proposed method is applied to creating images of outdoor scenes to demonstrate its usefulness.
  • 岩崎慶, 土橋宜典, 西田友是  Visual Computing グラフィクスとCAD合同シンポジウム予稿集  2001-  19  -24  2001/06/21  [Not refereed][Not invited]
  • MUKAIDANI Hiroaki, NITTA Tomoaki, DOBASHI Yoshinori  計測自動制御学会論文集  37-  (4)  316  -324  2001/04/30  [Not refereed][Not invited]
  • Satou Tomoya, Dobashi Yoshinori, Yamamoto Tsuyoshi  Proceedings of the IEICE General Conference  2001-  (2)  275  -275  2001/03/07  [Not refereed][Not invited]
  • Y. Dobashi, T. Yamamoto, T. Nishita  Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers  55-  (7)  1019  -1024  2001  [Not refereed][Not invited]
     
    An important element in enhancing the reality of computer graphics is the effect of atmospheric scattering. This effect creates shafts of light when atmospheric particles are illuminated. We have developed an accurate and fast method for displaying shafts of light produced by studio spotlights. To calculate the intensity of the light reaching the viewpoint, multiple semi-transparent planes are placed in front of the viewpoint. The intensities of these planes are set to the intensities of the light reaching the viewpoint. The shafts of light are displayed based on the intensities of the planes. These processes are accelerated by graphics hardware, using, in particular, color blending, texture mapping, shadow mapping, and multi-texturing functions. The proposed method renders the shafts of light very quickly, making it useful for designing lighting effects in sudios, on stages, and so on.
  • Dobashi Y, Nishita T, Okita T  全国大会講演論文集  59-  (4)  "4  -147"-"4-148"  1999/09/28  [Not refereed][Not invited]
  • KANEDA Kazufumi, TOMIDA Kazuhiro, YAMASHITA Hideo, DOBASHI Yoshinori  The Journal of the Institute of Image Electronics Engineers of Japan  28-  (4)  349  -357  1999/08/25  [Not refereed][Not invited]
  • Tsumura Hisashi, Okita Tsuyosi, Dobashi Yoshinori  IEICE technical report. Nonlinear problems  99-  (42)  23  -30  1999/05/14  [Not refereed][Not invited]
     
    Due to development of system science and various social requirements, we have encountered various complicated nonlinear system. In the identification of system whose a priori information of structure is poor, adequate candidate models may not be hypothesized. This paper proposes the system identification method in which the GA may be applied to generate the candidate models. The models are evaluated by Bayesian theorem in consideration of the reliability of the a posteriori probability. The availability of this proposed method is shown by digital simulations.
  • Dobashi Yoshinori, Nishita Tomoyuki, Okita Tsuyoshi  Proceedings of the IEICE General Conference  1999-  (2)  314  -314  1999/03/08  [Not refereed][Not invited]
  • DOBASHI Yoshinori, NAKATANI Hideki, KANEDA Kazufumi, YAMASHITA Hideo  The Journal of the Institute of Image Electronics Engineers of Japan  27-  (4)  349  -359  1998/08/25  [Not refereed][Not invited]
  • KANEDA Kazuhumi, YAMAMOTO Kazunori, DOBASHI Yoshinori, YAMASHITA Hideo  Proceedings of the conference on computational engineering and science  2-  (2)  487  -490  1997/05/28  [Not refereed][Not invited]
  • Dobashi Yoshinori, Kaneda Kazufumi, Yamashita Hideo, Nishita Tomoyuki  IPSJ SIG Notes  96-  (98)  1  -8  1996/10/09  [Not refereed][Not invited]
     
    Volume rendering is an important technique in scientific visualization, as this method can visualize the three-dimensional distribution of a scalar field. In order to visualize a time variant scalar field, a great deal of time has to be spent on generating images since the scalar field must be rendered at every sampled time. Generally, the time variant scalar field has coherency between frames. In this paper, by exploiting the coherency, a fast method for generating images is proposed. In the proposed method, volume data is transformed into wavelet to eliminate the redundancy. This makes it...
  • YAMAMOTO Kazunori, DOBASHI Yoshinori, KANEDA Kazuhumi, YAMASHITA Hideo  Proceedings of the conference on computational engineering and science  1-  (1)  27  -30  1996/05/29  [Not refereed][Not invited]
  • DOBASHI Yoshinori, KANEDA Kazufumi, YAMASHITA Hideo, NISHITA Tomoyuki  The Journal of the Institute of Image Electronics Engineers of Japan  24-  (3)  196  -205  1995/06/25  [Not refereed][Not invited]
  • Dobashi Yoshinori, Kaneda Kazufumi, Nakatani Hideki, Yamashita Hideo, Nishita Tomoyuki  全国大会講演論文集  50-  (2)  421  -422  1995/03/15  [Not refereed][Not invited]
     
    近年、コンピュータ・グラフィックスが照明設計に多く利用されるようになってきている。コンピュータ・グラフィックスを用いれば、照明器具の種類や輝度等を変更し、様々な視点から、視覚的に事前評価を行なうことができる。しかし、これまでのレンダリング手法では、光源の種類を変更した場合には、全ての計算をはじめからやり直さなくてはならないため、画像作成に時間がかかり、インタラクティブに画像生成を行うことは困難であった。本論文では、この問題を解決する方法として、点光源の配光特性を基底関数を用いて表現し、視点や光源に関するパラメータを変更した場合でも、高速に画像生成の行なえるインタラクティブ照明設計システムを提案する。

Awards & Honors

  • 2014 文部科学省 文部科学大臣表彰 科学技術賞
     CG映像制作のための演出技術の数理モデルに関する研究 
    受賞者: 安生;落合,土橋
  • 2012 Institute for Systems and Technologies of Information, Control and Communication Best Student Paper Award
     Visual Simulation of Magnetic Fluids 
    受賞者: T. Ishikawa;Y. Yue;K. Iwasaki;Y. Dobashi;T. Nishita
  • 2009 芸術科学会・NICOGRAPH CG国際大賞受賞特別賞
     Feedback Control of Cumuliform Cloud Formation based on Computational Fluid Dynamics 
    受賞者: 土橋,楠元;西田,山本
  • 2009 Institute for Systems and Technologies of Information, Control and Communication Best Paper Award
     An Inverse Problem Approach to BRDF Modeling 
    受賞者: K. Iwasaki;Y. Dobashi;F. Yoshimoto;T. Nishita
  • 2008 情報処理学会グラフィクスとCAD研究会 優秀研究発表賞
     Horizon Mapを用いた地形の効率的かつリアルなレンダリング 
    受賞者: 土橋宜典
  • 2007 情報処理学会グラフィクスとCAD研究会 優秀研究発表賞
     事例ベースアプローチによる動的な雲の多重散乱を考慮した効率的レンダリング 
    受賞者: 土橋宜典
  • 2006 情報処理学会グラフィクスとCAD研究会 優秀研究発表賞
     重なり格子を用いた流体のビジュアルシミュレーション 
    受賞者: 土橋宜典
  • 2001 情報処理学会北海道支部 奨励賞
     コンピュータグラフィックスを用いたリアルな画像生成のためのレンダリングパラメータ決定支援手法 
    受賞者: 土橋宜典
  • 1997 情報処理学会グラフィクスとCAD研究会・画像電子学会Visual Computing研究会 研究奨励賞
     
    受賞者: 土橋宜典
  • 1997 電気学会 論文発表賞B
     
    受賞者: 土橋宜典
  • 1996 画像電子学会 優秀論文賞
     天空光照度の基底関数表現を用いた屋外環境下における高速レンダリング法 
    受賞者: 土橋,金田;山下,西田
  • 1995 EUROGRAPHICS Best Paper Award
     A Quick Rendering Method using Basis Functions for Interactive Lighting Design 
    受賞者: Y. Dobashi;K. Kaneda;E. Nakamae;H. Yamashita;T. Nishita

Research Grants & Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2023/04 -2027/03 
    Author : 佐藤 周平, 土橋 宜典, 岩崎 慶
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2023/04 -2026/03 
    Author : 土橋 宜典, 佐藤 周平
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2022/04 -2025/03 
    Author : 井尻 敬, 土橋 宜典, 小檜山 賢二
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2021/04 -2025/03 
    Author : 岩崎 慶, 土橋 宜典
     
    実世界の材質の反射率(BRDF)を，波長を考慮して計測した計測スペクトラルBRDFの表現力を高めるために，計測スペクトラルBRDFを解析し編集する手法の研究開発を行なっている．2021年度は，反射率の5次元テーブル(入射方向2次元・反射方向2次元・波長1次元)である計測スペクトラルBRDFを，解析モデルによるパラメトリック表現する手法の研究開発を行なった．具体的には，広く用いられているCook-Torrance BRDFモデルへのフィッティングを行なっている．フィッティング精度を定量的に評価するために，スペクトラルレンダラの実装も行った． また，本来2023年度に実施予定であった，計測スペクトラルBRDFの意味的解析も同時に行なった．具体的には，計測スペクトラルBRDFを拡散反射成分と鏡面反射成分に分離する手法を開発した．拡散反射成分を方向成分と波長成分に分離し，鏡面反射成分を方向成分と方向によって色が変化する波長成分に分離するモデルを開発した．これにより，従来手法よりも精度良く元の計測スペクトラルBRDFを再現することが可能となった．また，拡散・鏡面反射成分の方向成分を主成分分析することでハイライトの鋭さや大きさを編集することを可能とした．さらに，Belcourらが提案した，構造色を考慮したフレネル反射モデルを用いて，鏡面反射成分の色成分をフィッティングすることで，鏡面反射成分の色を編集する手法も実装した．
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2020/11 -2025/03 
    Author : 神谷 之康, 土橋 宜典
     
    本研究課題では、脳-機械信号変換を3次元モデルに拡張することにより、3次元質感の脳内表現の解明を進めている。コンピュータビジョンやコンピュータグラフィックス分野で開発されてきた2次元画像から3次元構造への変換モデル（２D-3Dモデル）を、脳内の階層的情報表現のプロキシとして用いる。２D-3Dモデルの信号とfMRIで計測する脳活動信号を、脳デコーディングにもとづく脳-機械信号変換によって関連付けることで、世界の実在感を生み出す質感情報表現の解明を目指している。2021年度は、同一の刺激を入力したときのDNNモデルの活動値と脳の活動パターンの関係を定量化する一般的なアルゴリズムを完成させた。また、再構成画像に主観を反映させられることを実験的に証明する研究を発表した。２D-3Dモデルに関しては、ボクセルおよびメッシュ出力をもつモデルを探索し、脳活動パターンからのモデルの内部信号を高精度で予測できることを確認した。また、予測（デコード）されたモデルの内部信号から3次元形状を再構成するための基盤的技術を開発した。CG研究に関しては、物理方程式に基づいたリアルで立体感のある映像の生成のため、仮想物体の輝度および動きという二つの観点から研究を進めている。２０２１年度は、３次元質感を再現する基盤技術として、インタラクティブなパレットベースの色変換のための最適化手法を開発した。また、人工光源を考慮した夜空の効率的な描画に関する研究発表を行った。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2019/04 -2024/03 
    Author : 溝上 陽子, 土橋 宜典, 阿山 みよし, 石川 智治, 津村 徳道
     
    コンピュータグラフィックス技術を活用した照明の拡散度と質感再現の関係性の解明に関する研究を進めた。CG環境において照明の拡散度が物体の見えに与える影響を実験し、実空間での結果と比較検証した。実験刺激には3種類の質感の異なる球体を用いた。さらにその表面に凹凸を加えた刺激も追加して実験を行った。被験者は、複数の環境マップでレンダリングされた観察画像を観察することにより質感を記憶した。その後、7段階の拡散度条件でテスト刺激の質感再現評価を行った。CG環境における質感判断の安定性には、物体の素材および表面形状の影響が示唆される結果を得た。また、実空間において曲面を持つ立体や、明度や色が異なる場合に、照明の拡散度が様々な印象に影響を調べた。実験では、表面に正弦波状の凹凸を持つ無彩色の円柱、平面、および曲率を変えた刺激を、３段階の照明拡散度条件で観察し、光沢感と凹凸感を評価した。その結果、照明の拡散性と、光沢感・凹凸感の関係には、円柱の曲率による影響もあることが示唆された。 布の実際的なサンプルを用いた実験と検証も継続して行った。指向性光と拡散光を組み合わせた照明光下で凹凸のある一枚の布地を観察させた場合に、指向性光による明るい領域と拡散光によるそれ以外の領域の情報をどのように統合して布地全体の明度判定を行っているのかについて検討し、論文にまとめた。その他、照明の色と物体の色認識の関係、照明の距離が紙の表面反射特性に与える影響の測光的解析および質感知覚との関係、Web会議環境での照明が顔の見えに与える影響等についても検証した。
  • パラメータ調整が不要な誤差推定付き高精細画像生成技術の開発
    Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2018/04 -2021/03 
    Author : 岩崎 慶, 土橋 宜典
     
    本研究では，多光源レンダリング法に着目し誤差推定法を提案する．多光源レンダリング法は，多数の仮想的な点光源(Virtual Point Light, 以降VPLと略す)を用いて，輝度を計算する点（以降，シェーディング点と呼ぶ）への照明を表現する手法である．多光源レンダリング法は，アルゴリズムがシンプルで用途が広いため，商業用デザインソフトウェアにも採用されている．多光源レンダリング法では，高精細な画像を生成するために通常数十万から数百万のVPLを使用する．すべてのVPLを用いてシェーディング点での反射光の輝度を計算することは計算コストが高いため，VPLをクラスタリングして高速化する手法が主流となっている．しかしながら，VPLをクラスタリングする手法では，クラスタリングによる誤差を制御できていないという問題点がある．クラスタリングによる誤差はアーティファクトやノイズとして画像に現れるため，誤差を制御できないと，所望の画質を得るためにはクラスタリングに関するパラメータ調整の試行錯誤が必要となり，ユーザに多大な負担がかかる．本研究は，真値との誤差を精度よく推定し，誤差を制御することで，パラメータ調整を不要とする効率的かつ実用的な画像生成法を提案する．画質に関する2つの直感的なパラメータを指定するだけで，1度のレンダリング（画像生成）で所望の画質を得ることを目標とする． 2018年度は，関与媒質・アンチエイリアシング・被写界深度を考慮した画像生成における誤差推定法を提案した．従来手法であるMultidimensional Lightcutsと比較して，推定精度を2倍以上向上させた．
  • 多様な質感認識の科学的解明と革新的質感技術の創出
    Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Date (from‐to) : 2015/11 -2020/03 
    Author : 西田 眞也, 岩井 大輔, 堀内 隆彦, 佐藤 いまり, 中内 茂樹, 岡嶋 克典, 南本 敬史, 土橋 宜典, 神谷 之康, 佐藤 洋一, 梶本 裕之, 坂本 真樹
     
    （西田班）澤山が仏国INRIAに短期滞在して、固有画像分解に関する共同研究を進めた。独国Giessen大学からの実習生と弾性物体知覚の研究を立ち上げた。欧州質感プロジェクトであるDyViToとの連携も深めた。（南本班）米国NIHのRichmond博士ら３名を招聘し、サル局所脳活動のDREADD制御法、多点電極留置手術に関する技術支援を受け、価値判断や情動の神経回路基盤、側頭葉における質感情報処理機構についての共同研究を推進した。（土橋班）米国ノーザンブリア大学と羽虫の動きのシミュレーションに関する共同研究を実施した。Nelson Max (UC Davis)、Theodore Kim (Pixer)との共同研究も進めた。（梶本班）米国MITに滞在し、電熱ワイヤに熱を加えることによる高速な振動を触覚提示に利用する手法についてハードウエアの作成および評価を行った。（坂本班）音象徴語を用いた質感評価に対する国際比較研究の一環として、上海交通大学の呂研究室と、中国語話者を対象とする実験を行った。（岩井班）Punpongsanonが米国MIT CSAILのMueller研究室に短期滞在し、食べ物を出力する3Dプリンタを用いて、様々な食質感を生成する方法について議論し、内部構造や表面微細構造が食質感に与える影響を調査するための予備的な実験を進めた。（佐藤班）米国Simon Fraser大などとの共同研究を進めた。（岡嶋班）英国Oxford大学Spence研究室を訪問し、食品のクロスモーダル研究に関する研究打合せと予備実験を行なった。（堀内班）富永が米国の国際会議Electronic Imagingの質感関連のセッションに出席し、会議チェアの Ingeborg博士らと意見交換した。また、スタンフォード大学のWandell教授を訪問し蛍光物体の蛍光と反射の分光推定などについて討論をした。
  • コンピュータグラフィクスによる質感表現技術
    Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Date (from‐to) : 2015/06 -2020/03 
    Author : 土橋 宜典, 井尻 敬, 岡部 誠, 岩崎 慶, 藤堂 英樹
     
    質感の表現・解析・編集に関する研究、それぞれについて、本年度の成果を述べる。 ・質感の表現に関して：代表者の土橋は、任意の質感を表現可能な特殊な反射板の設計手法を1件の国際論文としてまとめ成果発表を行った。この成果は国内シンポジウムでの招待講演としても発表した。また、音の質感表現として、大気中の音の伝播解析を高速に行う手法を開発し、国内研究会にて成果発表を行い、技術論文賞を受賞した。この他、CGにおける簡易陰影表現（Ambient Occlusion）の高速計算など、3件の国内研究発表と1件の国際会議招待講演を行った。分担者の井尻は、深層学習を用いて文字の質感を転写する試みを開始し、その成果を1件の国内研究会と1件の国際会議にて発表した。また、これまでの成果をまとめたものを国際会議の招待講演として発表した。分担者の岩崎は、流体解析の高速化に関する研究を1件の国際論文誌にて発表した。また、輝度計算における誤差推定および微細構造物のBRDF推定法に関して、それぞれ、1件ずつ計2件の国内研究会にて発表を行った。前者を発展させた研究は国際会議にて発表した。分担者の藤堂は、散乱物体の高速レンダリング手法を開発し、国内研究会で発表した後、国際論文誌にまとめた。 ・質感の解析に関して：代表者の土橋は、透明物体の知覚的等価性に関する実験を行い、不透明物体の知覚的等価性との違いを明らかにし、国内研究会にて発表した。分担者の井尻は、VR環境下における3次元空間知覚に関して、双眼鏡により引き起こされる錯視に関する研究を国内研究会にて発表した。 ・質感の編集に関して：代表者の土橋は、流体の質感編集に関する研究を2件の国際論文としてまとめ成果発表を行った。これらは国内シンポジウムの招待講演としても発表した。分担者の岡部は、インタラクティブな動画修復手法を開発し、国内研究会にて発表した。
  • デジタル映像数学の構築と表現技術の革新
    科学技術振興機構：戦略的創造研究推進事業ＣＲＥST
    Date (from‐to) : 2010 -2015 
    Author : 安生健一
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2009 -2011 
    Author : YAMAMOTO Tsuyoshi, DOBASHI Yoshinori
     
    We have studied on architecture of annotation projection system that displays high-level information on 3D solid models created by rapid-prototype production machines. In the study, we developed a technique to measure 6 degree-of-freedom position of solid model and data structure of annotation data to be projected on it. We applied the experimental system to guidance system for 3D puzzle assembling game and confirmed that our system is applicable to guidance systems for complex parts assembling works.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2008 -2011 
    Author : DOBASHI Yoshinori, IWASAKI Kei
     
    We developed fast methods for the generating synthetic images of gaseous objects and deformable objects. These objects have been difficult to be handled and it took about several minutes to create an image of these objects. Our method creates a database in a preprocessing step to accelerate the image generation process. The proposed method made it possible to generate an image within 100 milliseconds.
  • ネットワーク情報配信プラットフォームとしての高自由度映像方式－ハイパーリンクムービーの実現－
    総務省：戦略的情報通信研究開発推進制度
    Date (from‐to) : 2005 -2007 
    Author : 長谷山美紀
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)
    Date (from‐to) : 2002 -2004 
    Author : 土橋 宜典
     
    本年度は、ポイントモデルを用いた仮想物体の高精度輝度計算、空・雲の高速表示の研究を行った。さらに、画像だけでなく、音まで加えることで仮想空間のリアリティの向上を図った。それぞれについて、概要を述べる。 ・ポイントモデルによる仮想物体の表示 本研究では、ポイントサンプルジオメトリのための相互反射計算法を開発した。サンプル点の集合で表現された3次元物体からメッシュを発生させることなく相互反射計算を行う。メッシュ構築の手間を軽減し、記憶容量の削減が実現できる。 ・空の高速表示 空の色を忠実に表現するために,天空光の輝度計算を多重散乱まで考慮して行う必要があるが,この多重散乱の計算は非常に複雑であり,膨大な計算コストがかかってしまう.本研究では,光の多重散乱の計算を効率よく行う手法を開発した。大気を仮想的な層(サンプリングシェル)に分割し,それらの層上での微粒子による散乱光の輝度分布を散乱マップと呼ぶテクスチャとして扱うことで,グラフィクスハードウェアを効果的に使用した手法を開発した. ・雲の高速表示 流体シミュレーションなどで得られる雲密度のボリュームデータを可視化するためには、光源方向の光の減衰とおよび視点方向の光の減衰を考えなければならない.従来法では、ボリュームデータを光源方向と視点方向にそれぞれ垂直にスライスを取ることによって減衰の計算を行っていた.本稿ではシャドウ・ビュースライスという光源方向と視点方向間のスライスを取ることにより、二つの計算のプロセスを統合し、従来法よりも計算コストを削減した手法を提案する. ・炎の音のシミュレーション 本研究では、炎によって生じる音のシミュレーション手法を提案する。炎の音は流体中の渦の非定常運動が主原因であるため、流体解析結果から渦度分布の時間変化から計算する。
  • 仮想空間におけるジオラマ作成システムの開発に関する研究
    中山隼雄科学技術文化財団：研究助成
    Date (from‐to) : 2002 -2002 
    Author : 土橋宜典

Educational Activities

Teaching Experience

  • Computer Graphics
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 情報科学院
    キーワード : コンピュータグラフィックス，写実的画像生成，物理ベースビジュアルシミュレーション
  • Information Media Environment
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 情報科学研究科
    キーワード : コンピュータグラフィックス，写実的画像生成，物理ベースビジュアルシミュレーション
  • Computer Graphics
    開講年度 : 2021
    課程区分 : 博士後期課程
    開講学部 : 情報科学院
    キーワード : コンピュータグラフィックス，写実的画像生成，物理ベースビジュアルシミュレーション
  • Information Media Environment
    開講年度 : 2021
    課程区分 : 博士後期課程
    開講学部 : 情報科学研究科
    キーワード : コンピュータグラフィックス，写実的画像生成，物理ベースビジュアルシミュレーション
  • Computer Engineering
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : ノイマン型計算機，アドレス方式，命令語．中央処理装置，演算装置，記憶装置
  • Media Programming
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : オブジェクト指向プログラミング，C++，音声，画像，コンピュータグラフィックス
  • Freshman Seminar
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : コンピューターグラフィックス、画像処理、マルチメディア
  • Media Processing System
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : マイクロコンピュータ，割り込み処理，リアルタイムOS，インターフェース回路，マルチメディア処理，開発プロセス

Committee Membership

  • 2022/06 - Today   Elsevier   Editorial Board of Computers and Graphics Journal

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