Abstract from Some of My Papers (3/6)


114 papers

　TVC 2015, 2015-6

“Incompressibility-Preserving Deformation for Fluid Flows Using Vector Potentials"

by Syuhei Sato, Yoshinori Dobashi, Yonghao Yue, Kei Iwasaki, Tomoyuki Nishita

Abstract

Physically-based uid simulations usually re- quire expensive computation cost for creating realistic animations.We present a technique that allows the user to create various uid animations from an input uid animation sequence, without the need for repeatedly performing simulations. Our system allows the user to deform the ow eld in order to edit the overall uid behavior. In order to maintain plausible physical be- havior, we ensure the incompressibility to guarantee the mass conservation. We use a vector potential for repre- senting the ow elds to realize such incompressibility- preserving deformations. Our method rst computes (time-varying) vector potentials from the input veloc- ity eld sequence. Then, the user deforms the vector po- tential, and the system computes the deformed velocity eld by taking the curl operator on the vector potential. The incompressibility is thus obtained by construction. We show various examples to demonstrate the useful- ness of our method.
Key worlds; flow deformation, incompressibility, vector potential

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　TVC 2014, 2014-12

“Volume preserving viscoelastic fluids with large deformations using position-based velocity corrections"

by Tetsuya Takahashi, Yoshinori Dobashi, Issei Fujishiro, Tomoyuki Nishita

Abstract

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.
Key worlds; Fluid simulation ・ Viscoelasticity

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　IEVC 2014, 2014-10

“Visual Simulation of Glazed Frost Taking into Accoun Supercooled State"

by Tomokazu Ishikawa, Yonghao Yue, Taichi Watanabe, Kei Iwasaki, Yoshinori Dobashi, Masanori Kakimoto, Kunio Kondo, Tomoyuki Nishita

Abstract

We propose a method for simulating glazed frost by computing heat transfers between water droplets and the surrounding air. Motions of air and water droplets are computed based on a FLIP (Fluid-Implicit-Particle)-based fluid solver. Glazed frost is a crystal clear ice and formed from supercooled raindrops that freeze when they hit object surfaces. We propose a method to create an animation of glazed frost formation by taking into account the heat transfer between particles and the out-side grids. The time to freeze is calculated by consider-ing the heat flux on the surface of the raindrop until freezing from the adhesion on the obstacles. We propose a technique which is highly compatible for a FLIP method to solve the heat conduction equation and we reproduce the formation of glazed frost.
Key worlds;

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　Computer & Graphics 2014, 2014-7

“Fast simulation of viscous fluids with elasticity and thermal conductivity using position-based dynamics "

by Tetsuya Takahashi, Issei Fujishiro, Tomoyuki Nishita

Abstract

Viscous fluids are ubiquitous, and reproducing their damped motions has been in demand for many applications. The most prevalent approach to simulating viscous fluids is based on the Navier?Stokes equations and necessitates viscosity integration. However, to simulate viscous fluids in a numerically stable manner, using explicit viscosity integration severely restricts time steps and requires an excessively long period for computation. In this paper, we propose a novel particle-based Lagrangian method for efficiently simulating viscous fluids by adopting position-based constraints. Our method uses the geometric configuration of particles for the positional constraints to approximate the dynamics of viscous fluids using position-based dynamics; thus the method can plausibly generate their motions while allowing for the use of much larger time steps than those previously adopted in the viscous fluid simulations. We also propose an associated boundary-handling scheme for position-based fluids to precisely specify boundary conditions for the constraints. Additionally, we reproduce elastic deformations of materials by controlling the constraints and incorporate thermal conduction into our framework to simulate resultant changes in particle properties and phase transition in the materials. By adjusting parameters, our method can encompass complex motions of fluids with different properties in a unified framework. Several examples demonstrate the effectiveness as well as versatility of our method.
Keywords: Fluid simulation; Viscous fluid; Position-based dynamics; Geometric constraint; Elasticity; Thermal conductivity

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　CGI 2014, 2014-6

“A Velocity Correcting Method for Volume Preserving Viscoelastic Fluids"

by Tetsuya Takahashi, Issei Fujishiro, Tomoyuki Nishita

Abstract

We propose a new particle-based method for simulating viscoelastic fluids which preserve their volumes. Our method achieves the volume preservation by enforcing the incompressibility of fluid, while correcting particle velocities to approximate the dynamics of viscoelastic fluids without disturbing computations for the incompressible flow. We offer three schemes for correcting particle velocities. The first scheme employs Shape Matching proposed by M\"uller et al. to derive appropriate transformations of particle sets. The second computes attraction forces on the basis of Hooke's law to restrict particle motions. The third utilizes Position-Based Dynamics to restore the original relations of particle positions. The first scheme enables smooth transfers of deformation waves, the second is intuitive and simple, and the third is easy to tune parameters. We demonstrate that our method can preserve fluid volumes while generating plausible viscoelastic motions.

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　NICOGRAPH International 2014, pp.35-42, 2014-6

“Visual Simulation of Compressible Snow with Friction and Cohesion"

by Tetsuya Takahashi, Issei Fujishiro, Tomoyuki Nishita

Abstract

Recent advances in physically-based simulation have made it possible to simulate various kinds of natural phenomena. However, characteristic behavior of accumulated snow while being compressed due to pressure has been insufficiently simulated merely with a height field approximation. In this paper, we propose a new method for simulating compressible snow by approximating snow as a set of porous snow particles. We introduce a new parameter called durability for each porous snow particle, which represents the rate of undamaged snow structures. The compression of accumulated snow is achieved by absorbing the impact from solids on the snow by taking the durability of snow particles into account. In addition to the compressibility, we incorporate friction and cohesion into our simulation framework to represent various effects of accumulated snow. For enhanced visual reality, fine scale simulations are performed as a post-processing. Several examples demonstrate the versatility of our method.

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　IIEEJ Transactions on Image Electronics and Visual Computing (T-IEVC), Vol.1，No.1, 2013-12

“Visual Simulation of Magnetic Fluids Using Dynamic Displacement Mapping for Spike Shapes"

by Tomokazu Ishikawa, Yonghao Yue, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

Although several simulation methods have been proposed to analyze the behavior of magnetic fluids in the computational physics field, it is still not reasonably tractable to simulate the spiking phenomenon using fully physically based methods. To synthesize spike shapes, a procedural approach has been proposed in the computer graphics field recently for visual simulation, which, however, cannot simulate dynamic arrangement and deformation of spikes since the spike shapes are determined beforehand. To overcome this drawback, we propose an improved model to incorporate the dynamic behavior of the spikes. The model is based on the assumption that the spikes are attracted by an external magnetic field and that each spike repels the others because of their magnetization. The position of the spikes on the liquid surface are determined in the simulation, and the spike shape is mapped according to the direction of the magnetic field lines. The coordinates at which the spike protrudes from the liquid surface are calculated in the fluid simulation.

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HPG13　

“Efficient Divide-And-Conquer Ray Tracing using Ray Sampling"

by Kosuke Nabata, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

Divide-and-conquer ray tracing (DACRT) methods solve intersection problems between large numbers of rays and primitives by recursively subdividing the problem size until it can be easily solved. Previous DACRT methods subdivide the intersection problem based on the distribution of primitives only, and do not exploit the distribution of rays, which results in a decrease of the rendering performance especially for high resolution images with antialiasing. We propose an efficient DACRT method that exploits the distribution of rays by sampling the rays to construct an acceleration data structure. 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. Our method accelerates the tracing of many types of rays (primary rays, less coherent secondary rays, random rays for path tracing) by a factor of up to 2 using ray sampling.

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　Proc. of IEVC. 2012, 2B-3, 2012-11

“Efficient image registration for cartoon animation"

by Pablo Garcia Trigo , Yoshihiro Kanamori, Sei Imai, Yonghao Yue, Tomoyuki Nishita

Abstract

Image registration is a fundamental technique that finds correspondences between two images and plays an important role in automating the production of 2D hand-drawn animations. However, previous methods for image registration are slow due to the high num- ber of searches used to find correspondences, reducing their utility. In this paper, we propose a method for accelerating the image registration of 2D hand-drawn animations. The key idea is to use random searches and propagate good correspondences to reduce the number of comparisons. Our experiments demonstrate that our method achieves a speedup of more than eight times without sacrificing the matching quality.

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　Proc. of IEVC. 2012, 2B-5, 2012-11

“Simulating plant color aging taking into account the sap flow in the venation "

by Paulo Silva, Yonghao Yue, Bing-Yu Chen Tomoyuki Nishita

Abstract

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　Proc. of IEVC. 2012, 4B-1, 2012-11

“Face detection and face recognition of cartoon characters using feature extraction "

by Kohei Takayama, Henry Johan, Tomoyuki Nishita

Abstract

In this paper, we propose methods for face detection and face recognition of cartoon characters which appear in cartoons, comics, games, etc. These methods can be applied to various applications, such as character search, automatic character classification, and character image editing. Previous researches on face detection and face recognition of real people have been abundant, on the other hand, there are little researches on face detection and face recognition of cartoon characters. Using previous methods for real people, cartoon character faces can hardly be detected and recognized because the face features of cartoon characters differ greatly from those of real people in terms of size and shape. Our methods solve these problems by considering the face features of cartoon characters. Using our methods, face detection and face recognition for cartoon characters search can be performed with good accuracy.

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　Proc. of IEVC. 2012, 5B-5, 2012-11

“Visual simulation of magnetic fluid taking into account dynamic deformation in spikes"

by Tomokazu Ishikawa, Yonghao Yue, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

In the physical field, several simulation methods for magnetic fluids had been proposed to analyze magnetic fluids' behavior. However, from their results, we estimate that it is difficult to simulate the spike shapes using only fully physically-based methods. Therefore in our previous work, we proposed the method which synthesizes the spike shapes by employing the procedural approach for visual simulation of magnetic fluids. Because the spike shape has been determined beforehand, this method has a drawback, that this method cannot simulate the dynamic arrangement and deformation of spikes. To overcome this drawback, we propose a simulation model based on the assumption that the spikes are attracted by an external magnetic field and each spike repels each other by the magnetization of itself. The coordinates of the conical undersurface centers of spikes on the liquid surface are determined in the simulation and the spike shape is mapped according to the direction of magnetic field lines.

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　 The journal of the Society For Art and Science, Volume.11, No.4 (Proc. of NICOKGRAPH Int. 2012, pp.83-93, 2012-7)

“Progressive Photon Beams with Adaptive Free Path Sampling"

by Kentaro Suzuki, Yonghao Yue, Tomoyuki Nishita

Abstract

Photo-realistic rendering of participating media, such as steam, water, fire, and smoke, is an important research topic in the computer graphics field. We present a fast and physically based method for rendering participating media based on the progressive photon beams method. For this, we propose a new version using adaptive free path sampling technique and applying a new estimation method for light transmittance functions based on stratified sampling, which overcomes the deficiencies in the progressive photon beams method. Our method is able to take into account not only single but also multiple scattering of light inside the participating medium. Using our method, participating media with complex density distributions can be handled, as well as complex lighting conditions. Additionally, we can obtain images which are guaranteed to converge to exact solutions. Moreover, our method is implemented on a GPU, enabling fast computation of the solutions.

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　 The journal of the Society For Art and Science, Volume.11, No.4, pp.118-128, 2012-12 (Proc. of NICOKGRAPH Int. 2012, pp.20-26, 2012-7)

“Visual Simulation of Bubbles in Carbonated Water"

by Yoshihiro Kanamori, Takeshi Nishikawa, Yonghao Yue, Tomoyuki Nishita

Abstract

In this paper, we propose a simple method for simulating the generation, growth and motion of bubbles in carbonated water. Bubbles are known to be generated at small air pockets on the surfaces of objects, such as a glass or a stirrer, and on the microscopic dusts in carbonated water. The number of bubbles and their growth rates differ according to the materials of the objects. In addition, the motion of bubbles also differs according to the materials; bubbles slowly glide on plastic and acrylic surfaces whereas such motions cannot be seen on a stainless-steel surface. Our method can represent such differences by controlling the number of generation points (i.e., air pockets) and applying adhesion forces to make bubbles stick on the surfaces. Because bubbles in carbonated water are sufficiently small, our method regards bubbles as non-deformable spherical particles. We simulate the flow in carbonated water using a grid-based method, together with the two-way coupling technique between bubbles and the convective flow. Additionally, the collisions and fusions among bubbles are also handled to reproduce the complex behavior of bubbles.

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　Proc. of WSCG2012, pp.?, 2012-6

“Animation of Water Droplets on a Hydrophobic Windshield"

by Nobuyuki Nakata, Masanori Kakimoto, Tomoyuki Nishita

Abstract

Animation of water drops on a windshield is used as a special effect in advanced driving games and simulators. Existing water droplet animation methods trace the trajectories of the droplets on the glass taking into account the hydrophilic or water-attracting nature of the glass material. Meanwhile, in the automobile industry, usage of hydrophobic glass windshields has recently been a common solution for the drivers clear vision in addition to cleaning the water with wipers. Water drops on a hydrophobic windshield behave differently from those on a hydrophilic one. This paper proposes a real-time animation method for water droplets on a windshield taking account of hydrophobicity. Our method assumes each relatively large droplet as a mass point and simulates its movement using contact angle hysteresis accounting for dynamic hydrophobicity as well as other external forces such as gravity and air resistance. All of a huge number of still, tiny droplets are treated together in a normal map applied to the windshield. We also visualize the Lotus effect, a cleaning action by the moving droplets. Based on the proposed simulation scheme, this paper demonstrates the motion of the virtual water droplets on the windshield of a running vehicle model.

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　Proc. of GRAPP2012, pp.319-327, 2012-2

“Visual Simulation of Magnetic Fluids"

by Tomokazu Ishikawa, Yonghao Yue, Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

In this paper, we focus on simulation of 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. In the field of electromagnetic hydrodynamics, many methods have also been proposed for simulating such spike shapes based on numerical fluid analysis. However, those methods are computationally expensive and they typically require tens of hours just to simulate a single spike. We propose a more efficient method by combining a procedural approach and the SPH method (smoothed particle hydrodynamics). Our method simulates overall behaviors of the magnetic fluids using the SPH method and then synthesizes the spike shapes by using the procedural approach. We demonstrate our method can generate visually plausible results within a reasonable computational cost.

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　Proc. of MIG 2011,In Proc. of Motion in Games 2011, Allbeck JM and Faloutsos P (Eds.), Lecture Notes in Computer Science (LNCS) 7060,, 2011-12

“Twisting, Tearing and Flicking Effects in String Animations"

by Witawat Rungjiratananon, Yoshihiro Kanamori, Napaporn Metaaphanon, Yosuke Bando, Bing-Yu Chen and Tomoyuki Nishita

Abstract

String-like objects in our daily lives including shoelaces, threads and rubber cords exhibit interesting behaviors such as twisting, tearing and bouncing back when pulled and released. In this paper, we present a method that enables these behaviors in traditional string simulation methods that explicitly represent a string by particles and segments. We offer the following three contributions. First, we introduce a method for handling twisting effects with both uniform and non-uniform torsional rigidities. Second, we propose a method for estimating the tension acting in inextensible objects in order to reproduce tearing and flicking (bouncing back); whereas the tension for an extensible object can be easily computed via its stretched length, the length of an inextensible object is maintained constant in general, and thus we need a novel approach. Third, we introduce an optimized grid-based collision detection for an efficient computation of collisions. We demonstrate that our method allows visually plausible animations of string-like objects made of various materials and is a fast framework for interactive applications such as games.

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　Proc. of 2011, , 2011-12

“An interactive system for structure-based ASCII art creation"

by Katsunori Miyake, Henry Johan and Tomoyuki Nishita

Abstract

Non-Photorealistic Rendering (NPR), whose aim is to create artistic style images, is one of the important research topics in computer graphics. One example of NPR is an art form called ASCII art which represents pictures using charac- ter strings. ASCII art is commonly used in media that cannot display images or mainly use text, such as e-mail and bulletin board system. ASCII art can be categorized into two styles, tone-based style and structure-based style. The structure- based style can represent content by using less number of ASCII characters compared to the tone-based style. However, in general, it takes beginners a long time to create structure- based ASCII art. As such, an automatic method that creates structure-based ASCII art is required to reduce the tasks of ASCII art creation. In this paper, we propose an interactive system which cre- ates structure-based ASCII art. We provide four matching metrics for converting an image into an ASCII art.Based on experimental results, we found that the suitable matching metrics to produce visually pleasant ASCII art images de- pend on the type of the input images. Since our system can produce ASCII art images in a few seconds, users can create several ASCII art images using different matching metrics, then select the one they like the most.

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　Proc. of SCCG2011, pp.69-76, 2011-4

“Interactive Texturing on Objects in Images via a Sketching Interface"

by Kwanrattana Songsathaporn, Henry Johan and Tomoyuki Nishita

Abstract

In this paper, we propose an interactive system for texturing objects in images without reconstructing the full 3D models. To make the texturing process easy for users, we emphasize on intuitiveness, and our system lets users perform texturing via a sketching interface. In addition, our system provides simple tools for specifying occlusion and perspective of the texturing objects. To texture with our system, first, with the sketching interface, users design the normal vector fields of objects in images that they wish to paste textures on. Next, to depict the shapes of the objects, the textures are deformed according to the normal vector fields, and pasted in the images over the objects. Once the textures are pasted on the images, users can manipulate (move, scale and rotate) the textures, and see the textures deformed interactively as if the textures were pasted on 3D models. The proposed system is tested with various kinds of objects in images, and we show that our system supports texturing with textures of regular, near-regular and irregular types.

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Best Paper Award

　Proc. of SCCG2011, pp.77-82, 2011-4

“Local Optimization of Distortions in Wide-Angle Images Using Moving Least-Squares"

by Yoshihiro Kanamori, Nguyen Huu Cuong and Tomoyuki Nishita

Abstract

We present a fast algorithm for reducing the undesired distortions (e.g., bending of straight lines) that often appear in wide-angle images especially taken with fisheye lenses. Our method allows the user to intuitively specify curves to be straightened by using quadratic control curves, and then automatically warps the image based on moving least-squares (MLS) while minimizing distortions in the vicinity of the curves. Unlike previous methods, our method provides results instantly, and allows the user to manipulate curves to obtain better results once after the initial solution is given. We demonstrate the effectiveness of our method with a variety of wide-angle images, together with comparisons to related projections.

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　Proc. of SCCG2011, pp.35-38, 2011-4

“Modeling of Aurora Borealis Using the Observed Data"

by Tomokazu Ishikawa, Yonghao Yue,Kei Iwasaki, Yoshinori Dobashi and Tomoyuki Nishita

Abstract

In the field of Computer Graphics (CG), applications such as movies and games benefit from realistic visualizations of atmospheric phenomena because realistic visualizations increase applications’ attractiveness. Among the atmospheric phenomena, auroras are some of the most beautiful phenomena, which makes their visualization highly desirable for such applications. Physically, the generation of auroras depends on the solar activity. Since auroras can be observed only in high latitudes and their observation depends on the weather condition, it is extremely rare to observe auroras directly in nature. Therefore, modeling and visualizing the aurora borealis using CG are important. In previous visual simulation methods for aurora borealis, the fluctuations and the curls of aurora are modeled by using a simple model that treats the aurora as fluids and therefore does not reflect the actual phenomena. One of the reasons for using such approximate simulations is that the motions of the aurora borealis are not fully understood yet among the researchers. In this paper, we propose a model for visualizing the aurora borealis using data gathered from satellite observations. The observed data represents the electric fields and the distributions of Field-Aligned Current (FAC) in high latitudes. By using the captured data and simulating the virtual current circuits that take place in the ionosphere, our method models the shapes of the aurora borealis. We demonstrate that our simulation method can model time-varying aurora borealis.

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　The Journal of IIEEJ, Vol.40, No.1, pp.6-13, 2011-1

“Deterministic Blue Noise Sampling by Solving Largest Empty Circle Problems"

by Yoshihiro Kanamori, Zoltan Szego and Tomoyuki Nishita

Abstract

Sampling patterns with a blue noise distribution are widely used in many areas of computer graphics, yet their efficient generation remains a difficult problem. We propose a method to generate point sets with a blue noise distribution using a deterministic algorithm with no preprocessing. We insert each new sample at the center of the largest empty circle in the point set, which is obtained by calculating the Delaunay-triangulation of the set and finding the triangle with the largest circumcircle. Our method supports adaptive sampling according to a user-specified density function, as well as specifying the exact number of required samples. It can also be extended to perform sampling on a three-dimensional curved surface.

Keywords Blue noise sampling, Delaunay triangulation, halftoning

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　The Journal of IIEEJ,Vol.40, No.1, pp.141-150, 2011-1

“Visual Simulation of Solar Photosphere Based on Magnetrohydrodynamics and Quantum Theory"

by T. Ishikawa, Y.Yue, Y. Dobashi, and Tomoyuki Nishita

Abstract

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.

Keywords

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　The Journal of IIEEJ, Vol.40, No.1, pp.105-113, 2011-1

“Real-Time Line Drawing of 3D Models Taking Into Account Curvature-Based Importance"

by Shohei Wada, H. Johan, Pablo Garcia Trigo, and Tomoyuki Nishita

Abstract

Keywords

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　Proc. of HC 2010, 2010-12

“Skeleton Extraction from a Mesh for Easy Skinning Animation"

by Martin Madaras, Roman Durikovic, Tomas Agoston, Tomoyuki Nishita

Abstract

This paper proposes the extraction of a skeleton and skinning weights from a given mesh, describes how to store computed data in Collada 1.5 and use it for an animation. Firstly, the mesh is contracted using constrained Laplacian smoothing in a few iterations. Few vertices from the contracted mesh are chosen as control points. Multiple edges are removed and vertices that are very close to each other are merged using a greedy algorithm minimizing the energy. The greedy selection is applied repeatable until we have the tree structure with edges corresponding to bones. We also propose the automatic assignment of the skinning weights that determine the rigid or soft mesh deformations. In the postprocessing stage the user can inspect the skeleton by previewing skinning deformations, make desired changes and export the skeleton to Collada 1.5. Transformation matrices used in a hierarchical skeleton tree are not transformed to joint's local transformation frame, so they are immediately compatible with majority of animation software and libraries.

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　Proc. of HC 2010, 2010-12

“Multi-touch Display using Combination of FTIR and HD LCD"

by Pavol Fabo, Roman Durikovic, Tomoyuki Nishita

Abstract

We present a multi touch display prototype based on optical tracking on commonly available LCD display. We describe several possible hardware configurations and discuss their problems. The output from this device is a video sequence that is processed to recognize the gestures. We propose a video preprocessing of input sequence and various applications of our multi touch system coupled with high definition LCD (HD LCD). By comparing the image preprocessing quality using possible setups we show that the method of frustrated total internal reflection (FTIR) gives the best results.

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　Proc. of CyberWorld 2010, 2010-10

“Interactive Lighting and Material Design for Cyberworlds"

by Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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, allfrequency 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.

Keywords: image-based lighting, interactive rendering, material design

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PG 2010　

“Fast Particle-based Visual Simulation of Ice Melting"

by Kei Iwasaki, Hideyuki Uchida, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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.

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　The Journal of IIEEJ,Vol.39, No.3, pp.369-375, 2010-7 (in Japanese)

“Glare Effect Aplication to Headramp Design Verification"

see
　 The Visual Computer, (Proc. CGI 2010) Vol.26, No.6-8, pp.659-667 2010-6

“Curling and clumping fur represented by texture layers"

by Paulo Silva, Yosuke Bando, Bing-Yu Chen, Tomoyuki Nishita

Abstract

Fur is present in most mammals which are common characters in both movies and video-games, and it is important to model and render fur both realistically and quickly. When the objective is real-time performance, fur is usually represented by texture layers (or 3D textures), which limits the dynamic characteristics of fur when compared with methods that use an explicit representation for each fur strand. This paper proposes a method for animating and shaping fur in real-time, adding curling and clumping effects to the existing real-time fur rendering methods on the GPU. Besides fur bending using a mass-spring strand model embedded in the fur texture, we add small scale displacements to layers to represent curls which are suitable for vertex shader implementation, and we also use a fragment shader to compute intra-layer offsets to create fur clumps. With our method, it becomes easy to dynamically add and remove fur curls and clumps, as can be seen in real fur as a result of fur getting wet and drying up.

Keywords : Fur Textures, Fur Curling, Fur Clumping, Real-Time Rendering

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dry fur -----> wet fur --- detail of wet fur
　 The Visual Computer, (Proc. CGI 2010) Vol.26, No.6-8, pp.883-891, 2010-6

“Visual Simulation of Mixed-motion Avalanches with Interactions Between Snow Layers"

by Yusuke Tsuda, Yonghao Yue, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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 in fast speed, often resulting in impressive visual effects. The mixed-motion avala- nche 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 denseflow 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.

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　 The IEICE Transactions of Information and Systems (Japanese edition), D, Vol.J92-D, No.9 pp.1613-1620, 2009-9 (in Japanese)

“Dual-quaternion Skinning with Scaling"

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　The Journal of IIEEJ, Volume 38, pp.1108-116 (in Japanese) 2009-7

"Calculation and Interpolation of Reflectance and Transmittance Distribution of Scattering Materials "

see
　 The Journal of IPSJ, vol. 17, pp.180-190 (2009). (in Japanese)

"Rendering Translucent Materials with Plane-parallel Solution"

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　 The Journal of IPSJ, Vol.50, No.8, pp.1917-1925, 2009-8 (in Japanese)

"Inverse Problem Approach for BRDF Modeling"

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　 IEICE Transactions on Information and Systems, Vol.E92-D, No.6, pp.1289-1295, 2009-6

“Interactive Region Matching for 2D Animation Coloring Based on Feature's Variation"

by Pablo GARCIA TRIGO, Henry JOHAN, Takashi IMAGIRE and Tomoyuki Nishita

Abstract

We propose an interactive method for assisting the coloring process of 2D hand-drawn animated cartoons. It segments input frames (each hand-drawn drawing of the cartoon) into regions (areas surrounded by closed lines. E.g. the head, the hands) extracts their features, and then matches the regions between frames, allowing the user to fix coloring mistakes interactively. Its main contribution consists in storing matched regions in lists called "chains" for tracking how the region features vary along the animation. Consequently, the matching rate is improved and the matching mistakes are reduced, thus reducing the total effort needed until having a correctly colored cartoon.

Key words: 2D animation, coloring, matching

Additional information
　 The Journal of Visualization and Computer Animation Volume 20, issue 3-4 (CASA 2009), 2009-6

"Deformation and fracturing using adaptive shape matching with stiffness adjustment"

by Makoto Ohta, Yoshihiro Kanamori, Tomoyuki Nishita

Abstract

This paper presents a fast method that computes deformations with fracturing of an object using a hierarchical lattice. Our method allows numerically stable computation based on so-called shape matching. During the simulation, the deformed shape of the object and the condition of fracturing are used to determine the appropriate detail level in the hierarchy of the lattices. Our method modifies the computation of the stiffness of the object in different levels of the hierarchy so that the stiffness is maintained uniform by introducing a stiffness parameter that does not depend on the hierarchy. By merging the subdivided lattices, our method minimizes the increase of computational cost.

KEY WORDS: interactive deformation; soft body; shape matching; fracturing

Additional information
　 The Visual Computer, 25, (Proc. of CGI2009), pp.719-727, 2009-6.

"A Fast Method for Simulating Destruction and the Generated Dust and Debris"

by Takashi Imagire, Henry Johan, Tomoyuki Nishita

Abstract

Simulating the destruction of objects due to collisions has many applications in computer graphics. Previous methods on the destruction of objects perform physically-based simulation of the fracture of objects into relatively large size fragments. However, if we observe the process of the destruction of objects, we can see that dust and fine debris are also generated. In particular, previous methods do not take into account the dust generation. In this paper, we present a unified framework for simulating destruction and the generated dust and various sizes of debris. Our method simulates destruction on three different scales: coarse fracture, fine debris and dust. We compute the distribution and the amount of fine debris and dust based on the fracture energy which is the energy that causes the object to be fractured.We demonstrate the effectiveness of the proposed method, in terms of the generated effects and the simulation speed, by showing the simulation results of destruction caused by the collision between objects.

Additional information
　 Proc. of GRAPP 2009, pp,129-136, 2009-2.

"AN INVERSE PROBLEM APPROACH TO BRDF MODELING"

by Kei Iwasaki, Fujiichi Yoshimoto, Tomoyuki Nishita and Yoshinori Dobashi

Abstract

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.

Additional information
　 Proc. of CW08, pp., 2008-9.

"Construction of Autostereograms Taking into Account Object Colors and its Applications for Steganography"

by Y. Tsuda, Y, Yue,,Tomoyuki Nishita

Abstract

Information on appearances of three-dimensional objects are transmitted via the Internet, and displaying objects plays an important role in a lot of areas such as movies and video games. An autostereogram is one of the ways to represent threedimensional objects taking advantage of binocular parallax, by which depths of objects are perceived. In previous methods, the colors of objects were ignored when constructing autostereogram images. In this paper, we propose a method to construct autostereogram images taking into account color variation of objects, such as shading. We also propose a technique to embed color information in autostereogram images. Using our technique, autostereogram images shown on a display change, and viewers can enjoy perceiving three-dimensional object and its colors in two stages. Color information is embedded in a monochrome autostereogram image, and colors appear when the correct color table is used. Our technique can also be used for steganography to hide color information. Moreover, file size gets smaller than that of an original autostereogram image because indexed colors are used. Therefore, the 3D images constructed using our method are useful for tranmission through the cyberworld.

Additional information
　 The Visual Computer, Volume 24, Numbers 7-9 pp.753-763, 2008-9.

"A virtual painting knife"

by Naoto Okaichi, Henry Johan, Takashi Imagire1, and Tomoyuki Nishita

Abstract

Recently, in the area of non-photorealistic rendering, there has been a significant effort in digital painting research to simulate traditional painting styles and painting pigments. In particular, the simulation of painting tools is very important because this enables an intuitive painting experience for a user and generates rich painting effects. Many painting systems have been proposed using brushes, but less for other painting tools. As a result, there is still a limitation in the variety of painting effects that can be generated. In this paper, we propose a method to simulate painting using a painting knife, which is an important tool in oil painting. We model a painting knife and model the pigments such that the system is suitable for realizing the impasto style. We also present a technique for simulating the interaction between a painting knife and pigments on a canvas in real-time.

Keywords Non-photorealistic rendering - Painting systems - Painting knife model

Additional information
　 IECV2007, 2007-11.

"FLUID SIMULATION BY PARTICLE LEVEL SET METHOD WITH AN EFFICIENT DYNAMIC ARRAY IMPLEMENTATION ON GPU"

by Yasuhiro Matsuda, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

We propose an efficient method to treat dynamic array data on Graphics Processing Unit (GPU), which is applicable to fluid simulations. Few numbers of dynamic structures have been realized on GPU since most of the previous methods store the data in texture to represent the structure and it is difficult to manage the dynamic structure on the texture. Our method uses vertex buffer object for representing the data structure and combines the transform feedback and the geometry program, which are the functionalities of GPU. Our method offers a simple but an efficient way of realizing dynamic array on GPU. Furthermore we apply our method to the implementation of a particle level set method. The particles data are represented by our dynamic array and they are updated, added, and deleted completely on GPU. By using the method, a fast and accurate fluid simulation can be realized.

Additional information
　 Journal of IIEEJ, Vol.37, No.3 pp.196-205, 2008-5.

"REAL-TIME REFLECTION AND REFRACTION ON A PER-VERTEX BASIS"

by Masanori Kakimoto,Tomoaki Tatsukawa,Geng Chun,Tomoyuki Nishita

Abstract

This paper proposes a novel method for real-time rendering of polygon mesh surfaces with reflection or refraction. The basic process is similar to dynamic environment mapping or cube mapping. Our proposed method is superior to those in that the accurate ray direction is reflected in the resulted image at every vertex on the mesh. Existing real-time techniques suffer from the differences between the viewpoint for the environment map and each reflection point. The proposed method minimizes this by finding an optimal viewpoint for the reflective or refractive mesh. With a sufficient number of vertices and map image resolutions, the users can render reflected images as accurate as ray tracing for all practical purposes, except for reflected objects around ray converging points of reflection on concave surfaces or refraction through convex lenses. The method can be applied to areas which require accuracy such as industrial design. Experiments with a CAD model of a car rear-view mirror and spectacle lenses exhibited results of sufficient quality for design verification. cube mapping suffice. For example, automobile designers need to check the reflecting image on the rearview mirror under design and are forced to use ray tracing. Our method enables them to verify the reflection/refraction result in real-time.

Additional information
　 The Visual Computer, Vol. 24, No. 2, pp.77-84. 2008-2.

"GPU-based rendering of point-sampled water surfaces"

by Kei Iwasaki, Yoshinori Dobasi, F.Yoshimoto, Tomoyuki Nishita

Abstract

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 the 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 presents 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.

Additional information
　 Journal for Geometry and Graphics, Volume 11, No. 2, 237-247. 2007-.

"An Educational Non-Photorealistic Rendering System Using 2D Images by Java Programming" Journal for Geometry and Graphics"

by Kunio Kondo, Tomoyuki Nishita, Hisashi Sato, Koichi Matsuda,

Abstract

It is important to improve the teaching and tutoring materials avail- able in undergraduate CG education. Exposure to such material will certainly help encourage CG research. However, new image generation algorithms proposed in recent research are not usually included in tutoring material at the undergraduate level. We, the authors, have developed teaching material designed for educating undergraduates in CG. This paper describes teaching materials that support the study of NPR, or “non-photorealistic processing”, a painting-style image process- ing technique used in CG education. Our goal is to make a tutoring system for studying NPR through Java programming. First, we will introduce “Jimmy”, an educational Java software program for NPR. Jimmy supports a new brush and filtering functions for painting-style images. Second, we introduce a “CG Ex- periment Course Syllabus” for using the proposed system, and we describe the outcomes of its exercises. Students can develop new brush, filtering, and drawing techniques for painting-style images by extending and modifying the algorithms. Through using our system we found the following results: (1) The proposed educational system was very useful for students in compre- hending an algorithm by extending the existing source of the algorithm, and the students were able to comprehend various painting processing methods by devel- oping new image filters. (2) The proposed educational system spurred an increase in the number of stu- dents interested in non-photorealistic image generation techniques.

Additional information
　 PG2007, pp.87-96, 2007-10.

"Global Illumination for Interactive Lighting Design using Light Paths Precomputation and Hierarchical Histogram Estimation"

by Yonghao Yue, K. Iwasaki, Y. Dobashi, Tomoyuki Nishita

Abstract

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 perform 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.

Additional information
　 PG2007, pp.363-372, 2007-10.

"Towards Digital Refocusing from a Single Photograph"

by Yosuke Bando, Tomoyuki Nishita

Abstract

This paper explores an image processing method for synthesizing refocused images from a single input photograph containing some defocus blur. First, we restore a sharp image by estimating and removing spatially-variant defocus blur in an input photograph. To do this, we propose a local blur estimation method able to handle abrupt blur changes at depth discontinuities in a scene, and we also present an efficient blur removal method that significantly speeds up the existing deconvolution algorithm. Once a sharp image is restored, refocused images can be interactively created by adding different defocus blur to it based on the estimated blur, so that users can intuitively change focus and depth-of-field of the input photograph. Although information available from a single photograph is highly insufficient for fully correct refocusing, the results show that visually plausible refocused images can be obtained.

Additional information
　 EGSR2007, pp.35-44, 2007-6.

"Precomputed Radiance Transfer for Dynamic Scenes Taking into Account Light Interreflection"

by Kei Iwasaki, Y. Dobashi, F. Yoshimoto, Tomoyuki Nishita

Abstract

Fast rendering of dynamic scenes taking into account global illumination is one of the most challenging tasks in computer graphics. This paper proposes a new precomputed radiance transfer (PRT) method for rendering dynamic scenes of rigid objects taking into account interreflections of light between surfaces with diffuse and glossy BRDFs. To compute the interreflections of light between rigid objects, we consider the objects as secondary light sources. We represent the intensity distributions on the surface of the objects with a linear combination of basis functions. We then calculate a component of the irradiance per basis function at each vertex of the object when illuminated by the secondary light source. We call this component of the irradiance, the basis irradiance. The irradiance is represented with a linear combination of the basis irradiances, which are computed efficiently at run-time by using a PRT technique. By using the basis irradiance, the calculation of multiple-bounce interreflected light is simplified and can be evaluated very quickly. We demonstrate the real-time rendering of dynamic scenes for low-frequency lighting and rendering for all-frequency lighting at interactive frame rates.

Additional information
　 NICOGRAPH International 2007, 2007-5.

"Intuitive Path-based Camera Control for Dynamic Scenes"

by Aritoki Kawai, Tsuneya. Kurihara, Tomoyuki Nishita

Abstract

This paper presents an intuitive user interface for a virtual camera controlled by a path and a set of constraints. Here, the constraints mean where an object is to be projected on the screen. In many cases, the camera position plays a more important role than other settings such as the orientation and the field of view angle of the camera. Therefore, in this paper, the user sets the camera path and the screen constraints, and then, both the orientation and the field of view angle are computed automatically. Thanks to the low computational cost in the presented method, real time control is possible. We generate several sample animations to confirm the effectiveness of this method.

Additional information
　 The Visual Computing, Volume 23, Issue 9 (CGI07), pp.697 - 705 2007-8.

"A Fast Rendering Method for Clouds Illuminated by Lightning Taking into Account Multiple Scattering"

by Yoshinori Dobashi, Y. Enjyo,T, Yamamoto, Tomoyuki Nishita

Abstract

Methods for rendering natural scenes are used in many applications such as virtual reality, computer games, and ?ight 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. In the proposed method, 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.

Additional information
　 The Visual Computer, Volume 23, Numbers 9-11, pp. 935-944 (CGI2007), 2007-9.

"Anti-Aliased and Real-Time Rendering of Scenes with Light Scattering Effects"

by Takashi Imagire, Henry Johan, Naoki Tamura, Tomoyuki Nishita

Abstract

Recently, for real-time applications such as games, the rendering of scenes with light scattering effects in the presence of volumetric objects such as sm oke, mist, etc, has gained much attention. Slice-based methods are well known techniques for achieving fast rendering of these effects. However, for real-ti me applications, it is necessary to reduce the number of slice planes that are used. As a result, aliasing (striped patterns) can appear in the rendered ima ges. In this paper, we propose a real-time rendering method for scenes contain ing volumetric objects that does not generate aliasing in the rendered images. When a scene consists of volumetric and polygonal objects, the proposed method also does not generate aliasing at the boundaries between the polygonal and the volumetric objects. Moreover, we are able to reduce alia sing at shadows inside a volumetric object that are cast by polygonal objects by interpolating the occlusion rates of light at several loc ations. The proposed method can be efficiently implemented on a GPU.

Additional information
　 Proc. ACM Symposium Virtual Reality Software and Technology (VRST) 2006, pp. 91-99 2006-10.

"A Fluid Resistance Map Method for Real-time Haptic Interaction with Fluids"

by Yoshinori Dobashi, S. Hasegawa, M. Kato, M. Sato, T. Yamamoto, Tomoyuki Nishita

Abstract

Under construction

Additional information
TVC;　 the Visual Computer Journa, Vol.22, No.9-11, p.702 - 712, 2006-10.

"A Practical and Fast Rendering Algorithm for Dynamic Scenes Using Adaptive Shadow Fields"

by Naoki Tamura, Henry Johan, Bing-Yu Chen, Tomoyuki Nishita

Abstract

Recently, a precomputed shadow fields method was proposed to achieve fast rendering of dynamic scenes under environment illumination and local light sources. This method can render shadows fast by precomputing the occlusion information at many sample points arranged on concentric shells around each object and combining multiple precomputed occlusion information rapidly in the rendering step. However, this method uses the same number of sample points on all shells, and cannot achieve real-time rendering due to the rendering computation rely on CPU rather than graphics hardware. In this paper, we propose an algorithm for decreasing the data size of shadow fields by reducing the amount of sample points without degrading the image quality. We reduce the number of sample points adaptively by considering the differences of the occlusion information between adjacent sample points. Additionally, we also achieve fast rendering under low-frequency illuminations by implementing shadow fields on graphics hardware.

Additional information
IEICE06;　 IEICE 2006, Vol.E89-D, No.9, pp.2562-2571

"Clustering Environment Lights for an Efficient All- Frequency Relighting"

by Henry Johan, Tomoyuki Nishita

Abstract

We present a novel precomputed radiance transfer method for efficient relighting under all-frequency environment illumination. Environment illumination is represented as a set of environment lights. Each environment light comprises a direction and an intensity. In a preprocessing step, the environment lights are clustered into several clusters, taking into account only the light directions. By experiment, we confirmed that the environment lights can be clustered into a much smaller number of clusters than their original number. Given any environment illumination, sampled as an environment map, an efficient relighting is then achieved by computing the radiance using the precomputed clusters. The proposed method enables relighting under very high-resolution environment illumination. In addition, unlike previous approaches, the proposed method can efficiently perform relighting when some regions of the given environment illumination change.

Additional information
CASA06;　 Proc. CASA 2006, pp.43-52, 2006-7.

"A Controllable Method for Animation of Earth-scale Clouds"

by Yoshinori Dobashi, Tsuyoshi Yamamoto, Tomoyuki Nishita

Abstract

Computer generated images of the earth are often used for space flight simulators, computer games, movies, and so on. Clouds are indispensable to the creation of realistic images in these applications. This paper proposes a method for animating clouds surrounding the earth. The method allows the user to control the motion of clouds by specifying the center positions of high/low atmospheric pressure areas on the earth’s surface. This data is used as input data and a three-dimensional velocity field is then calculated by solving Navier-Stokes equations. Water vapor is advected along the velocity field. Clouds are then generated due to the phase transition from water vapor to water droplets. We also propose an interactive system that enables the user to interactively control the simulation. The final photorealistic images are rendered by taking into account optical phenomena such as the scattering and absorption of light due to cloud particles.

Additional information
CGI06;　 Proc. of CGI2006, 2006-

"Real-time Rendering of Particle-based Fluid Simulation"

by Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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.

Additional information
NICOGRAPH06;　 CDROM of NICOGRAPH International2006, 2006-7

"Point-based Rendering of Water Surfaces with Splashes Simulated by Particle-based Simulation"

by Kei Iwasaki, Kaori Ono, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

Creating realistic animations of water is a challenging problem in the field of computer graphics. To create realistic animations of water, the fluid simulation of the movement of water is necessary. In recent years, attention has been paid to particle-based fluid simulation. Although several methods have been proposed to render the results of the particle-based simulation, there are few methods to render splashes. This paper presents an efficient rendering method for the results of the particle-based simulation with splashes. We calculate the water surfaces and the surfaces of the splashes by assigning the density to each particle and extracting iso-surfaces. The surfaces of the water and splashes are then sampled by points. This makes it possible to render the water surfaces and splashes efficiently by using point-based rendering.

Additional information
　 NICOGRAPH International 2006, 2006-5.

"A Fast Rendering Method for Shafts of Light in Outdoor Scene"

by Yoshitaka Moro, Ryo Miyazaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

Realistic rendering methods of natural phenomena in real-time have a variety of applications, such as flight simulators or computer games. The scattering effect due to atmospheric particles is one of the most important elements in creating realistic outdoor images. Shafts of light are caused by objects which shut out the sunlight, such as clouds and mountains. This paper proposes a method for creating outdoor images including shafts of light caused by mountains and clouds. In our method, shafts of light are displayed by subtracting the intensity of the shielded light. Our method is accelerated by using the fragment shader, which is a function of the latest graphics hardware.

Additional information
　 Computers & Graphics Volume 30, Issue 5, pp.767-778 2006-10.

"On pixel-based texture synthesis by non-parametric sampling"

by Seunghyup Shin, b, Tomoyuki Nishita and Sung Yong Shin

Abstract

In this paper, we propose a pixel-based method for texture synthesis with non-parametric sampling. On top of the general framework of pixel-based approaches, our method has three distinguishing features: window size estimation, seed point planting, and iterative refinement. The size of a window is estimated to capture the structural components of the dominant scale embedded in the texture sample. To guide the pixel sampling process at the initial iteration, a grid of seed points are sampled from the example texture. Finally, an iterative refinement scheme is adopted to diffuse the non-stationarity artifact over the entire texture. Our objective is to enhance texture quality as much as possible with a minor sacrifice in efficiency in order to support our conjecture that the pixel-based approach would yield high quality images.

Keywords:

Texture synthesis; Image processing; Non-parametric sampling

Additional information
art05;　 J. of the society for Art and Science pp.145-150, 2005-12

"Progressive 3D Animated Models for Mobile & Web Uses"

by Bing-Yu Chen , Sheng-Yao Cho, Henry Johan,Tomoyuki Nishita

Abstract

To date, more high resolution 3D animated models are required to present important details and fine structures, however, sometimes such high resolution models are un-necessary and undesired, especially on web and mobile phone environments. Though there are many well-known algorithms dealing well on simplifying 3D models, most of them are limited to static ones. Applying these mesh simplification methods to 3D animated models, a good simplified model in a specified pose can be obtained. However, some features of the original animated model, which can be shown in other poses, may be destroyed. In this paper, we propose an automatic method to simplify a 3D animated model which takes the features shown in every poses into account and preserves the geometry details of them. Therefore, a progressive 3D animated model can be generated for mobile or web uses.

Keywords:

Progressive Animated Models, Animated Model Simplification, LOD

Additional information
vis05;　 VIS05, pp. 495-502, 2005-10

"A Feature-Driven Approach to Locating Optimal Viewpoints for Volume Visualization"

by S. Takahashi, I. Fujishiro, Y. Takeshima, Tomoyuki Nishita

Abstract

Optimal viewpoint selection is an important task because it considerably influences the amount of information contained in the 2D projected images of 3D objects, and thus dominates their first impressions from a psychological point of view. Although several methods have been proposed that calculate the optimal positions of viewpoints especially for 3D surface meshes, none has been done for solid objects such as volumes. This paper presents a new method of locating such optimal viewpoints when visualizing volumes using direct volume rendering. The major idea behind our method is to decompose an entire volume into a set of feature components, and then find a globally optimal viewpoint by finding a compromise between locally optimal viewpoints for the components. As the feature components, the method employs interval volumes and their combinations that characterize the topological transitions of isosurfaces according to the scalar field. Furthermore, opacity transfer functions are also utilized to assign different weights to the decomposed components so that users can emphasize features of specific interest in the volumes. Several examples of volume datasets together with their optimal positions of viewpoints are exhibited in order to demonstrate that the method can effectively guide naive users to find optimal projections of volumes.

Keywords:

viewpoint selection, viewpoint entropy, direct volume rendering, interval volumes, level-set graphs

Additional information
CASA05;　 CASA05, pp.165-170, 2005-10

"A Fast Rendering Technique of Transparent Objects and Caustics"

by Kei Iwasaki, Fujiichi Yoshimoto, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

Rendering refractive caustics from transparent objects on opaque objects is computationally intensive. This paper presents a fast rendering technique for transparent objects and refractive caustics due to transparent objects on the opaque object. To calculate the intensities of caustics, we set virtual planes around the opaque object and store the intensities of caustics on the virtual planes as textures. Caustics are then rendered by using these textures. Our implementation, which additionally uses a GPU accelerator, enables us to render refractive caustics at interactive frame rates. We demonstrate this interactive rendering additionally for translation, rotation of both transparent objects and opaque objects, as well as for changing light and viewing directions.

Keywords:

caustics, transparent, refraction, global illumination, graphics hardwar

Additional information
CGI05;　 CGI05, pp.148-154

"A Method to Create Colored Pencil Style Images by Drawing Strokes Based on Boundaries of Regions"

by Hajime Matsui, Henry Johan, Tomoyuki Nishita

Abstract

A lot of Non-Photorealistic Rendering methods have been proposed for creating an artistic image from an image. In this paper, we propose a method for creating colored pencil style images. The feature of colored pencil drawings is that, though colored pencil drawings are drawn with limited number of colors of pencils, we can express a lot of colors and gentle textures by changing the strengths when drawing strokes and by overlapping strokes of different colors. In order to realize this feature, we determine which colors of pencils to use and how deep to push the pencils (equivalent to the strength when drawing strokes), then draw several types of strokes, such as strokes for outlines, basecoats, and shading, allowing the strokes to overlap each other. When we create strokes for shading, we make their directions to align along the boundaries of regions, resulting in images that are more like drawings made by human.

Additional information
IEICE2005;　 IEICE Transaction,E88-D: Special Issue on CyberWorlds, pp.904-911

"A Method for Fast Rendering of Caustics from Refraction by Transparent Objects"

by Kei Iwasaki, Fujiichi Yoshimoto, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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.

Additional information
NICO05;　 Nicograph International'05, pp.43-48,

"Visual Simulation of Spreading Fire"

by T. Ishikawa, Ryou Miyazaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

Visual simulation of fire is used as special effects in movies, applications of fire simulation for the training in disaster prevention. In this paper, we propose techniques for simulating fire spread taking into account the various properties of materials, and for an effective visualization of this phenomenon. In our simulation method, the flame dynamics is ob-tained by combining the Navier-Stokes equations and the heat conduction equation. The various com-bustion processes are simulated by specifying igni-tion points, the thermal diffusivity and calorie of chemical reaction depending on the types of materi-als. Moreover, in our method, fire is extinguished by reducing the fuel concentration. The reduction ratio of the fuel is based on the reaction kinetics theory developed in the field of chemistry. In our fire visu-alization method, the volume representing the fire is considered as a set of point light sources. The inten-sity of objects illuminated by the fire is calculated by accumulating the illumination due to the point light sources.

Additional information
CW2004;　 Proc. of CW2004 pp. pp.39-44

"A Rapid Rendering Method for Caustics Arising from Refraction by Transparent Objects"

by Kei Iwasaki, Fujiichi Yoshimoto, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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.

Additional information
artsci2004;　 Journal of artsci pp. 207-215

"Creating Watercolor Style Images Taking Into Account Painting Techniques"

by Henry Johan, Ryota Hashimoto, Tomoyuki Nishita

Abstract

Research for creating impressive images like paintings has attained more and more importance because of the recent growth in processing images. Among many painting styles, watercolor style gives a strong impression because of its thin colors and its soft appearance. This paper proposes a method to create watercolor style images from input images, for instance photographs. In contrast with the previously proposed watercolor methods that focuses only on simulating the effects of watercolor medium such as the mottled appearance and the color glazing, the proposed method also considers how the watercolor paintings are painted in order to simulate artists' painting techniques. In the proposed method, artists' painting techniques are represented using painting rules. Several painting rules are provided, in addition, user can specify their own painting rules. These painting rules are used for generating strokes to paint the objects. Painting techniques are simulated by first detecting the objects in the input image and generating strokes for each object according to the painting rules. The properties of watercolor medium are simulated by approximating each stroke with sampling points and diffuses their color to nearby pixels. Using the proposed method, a user can interactively create watercolor style images.

Key Words:

Watercolor painting, Painting techniques, Non-Photorealistic Rendering

Additional information
VRST 2004;　 Proc. of VRST 2004 pp.150 - 153

"An Efficient Representation of Complex Materials for Real-Time Rendering"

by Wan-Chun Ma , Sung-Hsiang Chao, Bing-Yu Chen, Chun-Fa Chang, Ming Ouhyoung, Tomoyuki Nishita

Abstract

To make the computer generated imagery (CGI) vivid, analyzing the appearance of materials becomes the first priority. Real world materials usually exhibit complex appearance and cannot be faithfully represented simply by analytical or parametric reflectance functions, such as the combination of bump, glossy, specular and diffuse maps which is widely used in current real-time rendering programs. In this paper, we propose an appearance representation for general complex materials which can be applied in real-time rendering framework. By combining a single parametric shading function (such as the Phong model) and the proposed spatial-varying residual function (SRF), this representation can recover the appearance of complex materials without much loss of visual fidelity. The difference between the real data and the parametric shading is directly fitted by a specific function for easy reconstruction. It is simple, flexible and easy to be implemented on programmable graphics hardware. We capture real photographs of different materials with a homemade lighting platform and use them to obtain the the data of SRF representation. Experiments show that the mean square error (MSE) between the reconstructed appearance and real photographs is less than 5%.

Additional information

CW2004;　Proc. of CW 2004 pp.210-215, 2004-11

"3D Character Model Creation from Cel Animation"

by Y. Ono, Bing-Yu Chen, Tomoyuki Nishita

Abstract

When creating a cel animation, the animators often use 3D character models to add some effects on the character or to generate intermediate images between the key frames. However, it is a troublesome and time-consuming task to create a 3D model. In this paper, we present an easy-to-use approach for creating a set of consistent 3D character models from the user-specified strokes on a 2D image sequence. The created consistent 3D models can be used in cel animation editing systems for adding shadowing effects, textures, etc. Moreover, since the vertices of the consistent 3D models have one-to-one correspondence among the frames, by using 3D morphing techniques, this approach can also be used to generate intermediate images between the key frames.

Additional information

CW2004;　Proc. of CW 2004

"Real-time Rendering of Bumpmap Shadows Taking Account of Surface Curvature"

by Koichi Onoue, Nelson L. Max, Tomoyuki Nishita

Abstract

The bump-mapping technique is often used to represent bumps on objects such as bark on trees and craters on the moon. In order to render shadows cast by bumps, the horizon map method was proposed. The horizon map is a table which has, for each of a small collection of azimuthal directions, slopes from each viewpoint on the bump map (height field) to the corresponding horizon point, which is the highest viewable point seen from that viewpoint. In this paper, we propose a more precise method for rendering bumpmap shadows using a both a horizon map and a distance map, to take curvature of surfaces into consideration. The distance map is a table which has, for each azimuthal direction, horizontal projected distances from each point of the bump map to its corresponding horizon point. The proposed method can render shadows efficiently by using programmable graphics hardware.

Additional information

PG2004;　

"Radiosity for Point-Sampled Geometry"

by Yoshinori Dobashi, Tsuyoshi Yamamoto, Tomoyuki Nishita

Abstract

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.

Additional information

PG2004;　

"A PROGRESSIVE REFINEMENT APPROACH FOR IMAGE MAGNIFICATION"

by Henry Johan, Tomoyuki Nishita

Abstract

The rapid growth in computer graphics and digital cameras has resulted in computer users being able to easily produce digital images. As a result, the need to display and print digital images has increased. Nowadays, high-resolution display and printing devices are available to users. Therefore, high-resolution images are needed in order to produce high quality displayed images and high quality prints. However, since high-resolution images are not usually provided, there is a need to magnify the original images. Previous methods on magnifying images have the disadvantage that either the sharpness of the edges cannot be preserved or that some distinct artifacts are produced in the magnified image. In this paper, we present a novel method for doubling the size of images in which the sharpness of the edges is preserved without introducing distinct artifacts in the magnified images. The proposed method consists of two steps, first generation of an initial magnified image and then progressively refining this image to produce a high quality magnified image. The experimental results show that with the proposed method it is possible to produce magnified images of comparable, and in some cases superior, visual quality to those produced using previous methods.

Additional information

PG2004;　

"Glare Generation Based on Wave Optics"

by Masanori Kakimoto, Kaoru Matsuoka, Tomoyuki Nishita, Takeshi Naemura and Hiroshi Harashima

Abstract

This paper proposes a novel and general method of glare generation based on wave optics. A glare image is regarded as a result of Fraunhofer diffraction, which is equivalent to a 2D Fourier transform of the image of given apertures or obstacles. In conventional methods, the shapes of glare images are categorized according to eyelash and their basic shapes (e.g. halos, coronas or radial streaks) are manually generated as templates, mainly based on statistical observation. Realistic variations of these basic shapes often depend on the use of random numbers. Our proposed method computes glare images fully automatically from aperture images and can be applied universally to all kinds of apertures, including camera diaphragms. It can handle dynamic changes in the position of the aperture relative to the light source, which enables subtle movement or rotation of glare streaks. Spectra can also be simulated in the glare, since the intensity of diffraction depends on the wavelength of light. The resulting glare image is superimposed onto a given computer-generated image containing high intensity light sources or reflections, aligning the center of the glare image to the high intensity areas. Our method is implemented as a multi-pass rendering software. By pre-computing the dynamic glare image set and putting it into texture memory, the software runs at an interactive rate.

Additional information

CGIM 2004;　

"A Fast Rendering Method of Clouds Using Shadow-View Slices"

by Ryou Miyazaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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”.

Key Words:

Clouds, Natural Phenomena, Atmospheric Effects, Volume Rendering, Graphics Hardware.

Additional information

IEICE2004;　

"An Effcient Cloud Visual Simulation Using Adaptive Grid Method"

by Ryou Miyazaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

Simulation of natural phenomena such as cloud, smoke, flame, and water are is an important research field in computer graphics. In particular, clouds play an important role in creating images of outdoor scenes. Fluid simulation is an effective method for creating realistic clouds although its computational cost is high. In this paper, we create realistic cloud animation using a numerical difference method for an atmospheric fluid model. Moreover, we consider a mountain as an obstacle, and simulate the cloud generated by the collision of the air current with a mountain, which could not be simulated in previous methods. To use the finite difference method, it is common to divide the space into grids. However, to create realistic clouds with high resolution, it is necessary to divide the space into a detailed grid, which increases the computational cost. Therefore, we introduce an adaptive grid method, which subdivides and rejoins the grid cells adaptively. This makes the simulation efficient by reducing the number of total grid cells. We show the cloud images produced using our approach and create some realistic animations.

Additional information

IIEEJ 2004;　Journal of IIEEJ, Vol.33, No.4, 2004-8 (in Japanese)

"A Calculation of Multiple Scattering Using Scattering Maps and An Efficient Method for Rendering Sky"

see
IIEEJ 2004;Journal of IIEEJ, Vol.33, No.4, 2004-8 (in Japanese)

"Animating Spattering Granular Material using Distinct Element Method"

see
CGI 2004;　Proc. of CGI 2004, pp.344-348 , 2004-6

"Real-time Rendering of Soap Bubbles Taking into Account Light Interference,"

by Kei Iwasaki, K, Matsuzawa, Tomoyuki Nishita

Abstract

In the field of computer graphics, simulation of physical phenomena is of great interest. We focus on the optical effects of soap bubbles. Soap bubbles have fascinating coloration and interesting physical properties. Therefore they are useful for the entertainment such as movies and games. Soap bubbles change their shapes by surface tension and external forces, and therefore their surface thickness also changes. Since the thickness of the soap bubble is several hundred nanometers, interference of the light occurs. This paper proposes a fast rendering method for the soap bubbles taking into account light interference and dynamics. In our method, the reflectivities of the thin film that is the cause of the light interference are calculated in advance and stored as textures. This makes it possible to render the deformable soap bubbles in real-time.

Additional information

PG 2003;　Proc. of Pacific Graphics 2003 (The 11th Pacific Conference on Computer Graphics and Applications), pp. , 2003-10

"Virtual Sandbox,"

by Koichi Onoue, Tomoyuki Nishita

Abstract

Interactive applications such as virtual reality systems have become popular in recent years. A ground surface composed of a granular material can be deformed when it comes into contact with an object, and, in this paper, we propose a deformation algorithm for the ground surface which is useful for such applications. The deformation algorithm is divided into three steps: (1) detection of the collision between an object and the ground surface, (2) displacement of the granular material, and (3) erosion of the material at steep slopes. The proposed algorithm can handle objects of various shapes, including a concave polyhedron, and a texture sliding technique is proposed to represent the motion of the granular materials. In addition, the proposed algorithm can be used at an interactive frame rate.

Additional information

PG 2003;　Proc. of Pacific Graphics 2003 (The 11th Pacific Conference on Computer Graphics and Applications), pp. , 2003-10

"Blending Multiple Polygonal Shapes,"

by Henry Johan, Tomoyuki Nishita

Abstract

Shape blending has several applications in computer graphics. In this paper, we present a new method for smoothly blending among multiple polygonal shapes. The blended shape is computed as a weighted average of the input shapes. The weight of each input shape is allowed to vary across the shape. This feature increases the flexibility for controlling the local appearance of the blended shapes. Our method computes the blended shape hierarchically, starting from the coarse version of the shape and adding the details gradually. Several examples are shown to demonstrate the advantages of the proposed method.

Additional information

PG 2003;　Proc. of Pacific Graphics 2003 (The 11th Pacific Conference on Computer Graphics and Applications), pp. , 2003-10

"Physics Motivated Modeling of Volcanic Clouds as a Two Fluids Model,"

by Ryoichi Mizuno, Yoshinori Dobashi, Bing-Yu Chen, Tomoyuki Nishita

Abstract

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.

Additional information

VG2003;　 Proc. of Volume Graphics 2003, pp.129-136, 2003-7

"A Volume Rendering Approach for Sea Surfaces Taking into Account Multiple Scattering Using Scattering Maps"

by Kei Iwaski, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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.

Additional information

CGI2003;　Proc. of CGI2003, pp.312-317, 2003-7

"Creating Various Styles of Animations Using Example-Based Filtering,"

by R. Hashimoto, H, Johan, Tomoyuki Nishita

Abstract

A number of Non-Photorealistic Rendering methods for producing artistic style images are proposed. Recently, a method called "Image Analogies" is proposed. This method is based on the notion of example-based filtering that uses a pair of images (an original image and a filtered image) as training data and generate an image which has a style that resembles the filtered image of the training data. This method has a great flexibility since the users can generate various styles of images by simply changing the training data. In this paper, we extend "Image Analogies" to generate various styles of animations. The coherence between frames is considered by computing the pixel flows between the frames. From experimental results, the proposed method can generate nice animation sequences.

Additional information

CGI 2003;　Proc. of CGI2003, pp.34-41, 2003-7

"An Efficient Mesh Simplification Method with Feature Detection for Unstructured Meshes and Web Graphics"

by Bing-Yu Chen, Tomoyuki Nishita

Abstract

This paper presents an efficient method of mesh simplification for geometric 3D models. The transmission of 3D models on the Internet is an important task. The data size of a 3D model is usually large to enable more detail to be represented. Hence, it is necessary to represent the 3D model while keeping the data size small and preserving its features, even if the meshes that constitute the model are unstructured. Although there are many methods for simplifying the meshes, most of them are time-consuming. Our approach is to obtain an adequate simplified model in a short amount of time. Therefore, the model provider can check the simplified result interactively before uploading to the server. After transmitting the simplified model, if the user at the client needs to get more details, by transmitting some necessary information, the progressively increasing model detail and the original model without losses could be reconstructed.

Additional information

img
IIEEJ 2003;　Journal of IIEEJ, Vol.32, No.4, 2003-7 (in Japanese)

"An Efficient Method for Displaying Marks on Soft Grounds Created by Objects"

see
IIEEJ 2003;　 Journal of IIEEJ, Vol.32, No.4, pp. 336-345, 2003-7 (in Japanese)

"A Real-Time Glare Rendering Technique Taking into Account Surface Reflection Attributes"

see
IEICE 2003;　 Journal of IEICE, pp.282-289, 2003-2

"A Rendering Method on Desert Scenes of Dunes with Wind-ripples"

by Kouichi Onoue, Tomoyuki Nishita

Abstract

This paper proposes a terrain formation method and a rendering method to synthesize realistic desert scenes. A desert terrain includes sand dunes and wind-ripples which are ripple patterns formed on a dune surface. We use two types of scale models to form them. Next, we put together the dunes and the wind-ripples, that is, we render the dunes with the wind-ripples by using the bump mapping technique with LOD (Levels Of Detail). We also take into account shadows due to the dunes and the wind-ripples.

Key Words:

desert, dunes, wind-ripples, Level of Detail, shadow, sand smoke

Additional information

CW2002;　Proc. of Cyber Worlds 2002, pp.472-479, 2002-11

"Free-Form Deformation with Automatically Generated Multiresolution Lattices"

by Yutaka Ono, Bing-Yu Chen, Tomoyuki Nishita, Jieqing Feng

Abstract

Developing intuitive and efficient methods for shape editing is one of the most important areas in computer graphics, and free-form deformation (FFD), which is one such methods, allows the user to deform a model easily by moving a set of control points, collectively called the lattice. Although the FFD method can be used for both global and local deformations, the user must define a suitable lattice manually or use a simple shaped lattice such as a parallelepiped. Therefore, we propose a new FFD method that automatically generates the lattices with which both types of deformations can be achieved. Our method refines a bounding box of the model and generates a set of finer lattices, which hierarchically ap- proximate the shape of the model. Through adjusting the control points of the generated lattices, both global and local deformations of the model can be achieved easily. Moreover, the method allows hierarchical deformation of the model by combining different levels of lattice.

Additional information

CW2002; 　Proc. of Cyber Worlds 2002, pp.465-471, 2002-11

"Topological Morphing Using Reeb Graphs"

by Pizzanu Kanonchayos, Tomoyuki Nishita, Shinagawa Yoshihisa, Tosiyasu L. Kunii

Abstract

Metamorphosis between 3D objects is often the trans- formation between a pair of shapes that have the same topology. This paper presents a new model using Reeb graphs and their contours to create morphing between 3D objects having different topology. The proposed method specifies the correspondence between of the input objects by using the graph isomorphic theory. Then the super Reeb graph, which has the equivalent topological infor- mation to the Reeb graphs of the two input objects, is con- structed and used to conduct the sequence of the morph- ing. The evolutions of the topology that occur during the morph can be specified by the transformation of the Reeb graphs and their contours of the input objects. Reeb graph-based modeling allows the users precisely and in- tuitively control the morph because the topological infor- mation of the objects, represented by the structures of the Reeb graphs, is explicit and easy to understand. Moreover, the contours of the Reeb graphs also represent the geo- metrical information of the objects. The examples of morphing between different topological shapes are dem- onstrated.

Additional information

IIEEJ 2002; Journal of IIEEJ, Vol.31, No.4, pp.468-476, 2002-7 (in Japanese)

"Network-based Walk-through System using Relief Textures as Distant View Billboards"

see ??
PG 2002;　Proc. of Pacific Graphics 2002 (The 10th Pacific Conference on Computer Graphics and Applications), pp.166-175, 2002-10

"A Simple Method for Modeling Wrinkles on Human Skin"

by Yosuke Bando, Takaaki Kuratate, Tomoyuki Nishita

Abstract

Realism of rendered human skin can be strongly enhanced by taking into account skin wrinkles. However, modeling wrinkles is a difficult task, and considerable time and effort are necessary to achieve satisfactory results. This paper presents a simple method to easily model wrinkles on human skin, nevertheless taking into account the properties of real wrinkles. Wrinkles are specified using intuitive parameters, and are generated over a triangle mesh representing a body part, such as a hand or a face. Wrinkled skin surfaces are rendered at an interactive frame rate, dynamically modulating wrinkle amplitude according to skin surface deformation while animating the body part. We demonstrate the ability of our method to model realistic wrinkle shapes by comparing them with real wrinkles.

Key Words:

wrinkle simulation, human skin rendering, facial animation,
human body simulation, texture mapping

Additional information

PG 2002; Proc. of Pacific Graphics 2002, pp.433-434, 2002-10

"Adaptive solid texturing for Web3D applications"

by Bing-Yu Chen, Tomoyuki Nishita

Abstract

Solid texturing is a well-known computer graphics tech-nology, but still has problems today, because it consumes too much time if every pixel is calculated on the fly or has a very high memory requirement if all of the pixels are storedin the beginning. Although some methods have been proposed, almost all of them need the support of spe-cific hardware accelerators. Hence, these methods could not be applied to all kinds of machines, especially the low-cost ones available over the Internet. Therefore, we pre-sent a new method for procedural solid texturing in this paper. Our approach could almost render an object with solid texturing in real-time using only a software solution. Furthermore, to demonstrate that our approach is widely applicable we choose pure Java for its implementation, since it could not receive any benefit from the hardware and could be executed on the Internet directly.

Additional information

VIIP 2002;　Proc. of the 2nd IASTED International Conference, pp.282-287, 2002-9

"3D Model Deformation along a Parametric Surface"

by Bing-Yu Chen, Yutaka Ono, Henry Johan, Masaaki Ishii, Tomoyuki Nishita, Jieqing Feng

Abstract

Free-Form Deformation (FFD) is an efficient technique for editing the shapes of 3D models, and widely used in Computer-Aided Design (CAD), computer animation, computer graphics entertainment etc. The basic idea of some famous previous FFD approaches deforms a target 3D model by adjusting some control points of a 3D lat-tice surrounding the model. It is a tedious work, espe-cially when the lattice contains too many control points. Moreover, how to place the control points of the lattice to make them cover the region of the target model is also a problem, and it is also difficult to keep the geo-metric measurement for the deformed model. Therefore, in this paper, a novel FFD method without any lattice-like structure is proposed by borrowing the idea of non-distortion texture-mapping for free-form surfaces. By using this method, the shape of the deformed model due to a given parametric surface can be predicted easily, so that the user can get his or her desirable results more intuitively and has no necessary to place the control points of a proper lattice. Moreover, since this method is simple, efficient, and has a real-time response, it is more suitable for doing the animation with thin objects.

Key Words:

3D model deformation, non-distortion, deformation, non-distortion mapping,
flattened surface, animation

Additional information

ICGG 2002;　Journal of 10th ICGG, Vol.2, pp.123-128, 2002-8

"DEVELOPMENT OF A WEB BASED TRAINING SYSTEM AND COURSEWARE FOR ADVANCED COMPUTER GRAPHICS COURSES ENHANCED BY INTERACTIVE JAVA APPLETS"

by Tomoyuki NISHITA, Kunio KONDO, Yoshio OHNO, Yoshiaki TAKAI, Kenjiro T. MIURA, Yoshinori DOBASHI, Satomi ISHIUCHI, Tokiichiro TAKAHASHI, Ayumi KIMURA, Ayumi MIYAI

Abstract

We propose a web-based training system and courseware for advanced computer graphics for undergraduate students. By using the system, the students have no temporal and spatial limitations for learning computer graphics technologies. Once they can connect to the Internet, they can study for as much time as they wish and in any place . We have designed more than 50 Java applets from the educational viewpoint, and developed them to enable complicated computer graphics algorithms to be comprehensibly understood. All of the applets have been developed by using pure Java programming language because of its hardware-neutral features and wide availability on many hardware platforms. Hence, the students can use any Java enabled browser on any kind of platform to study interactively computer graphics technologies via the system.

Key Words:

computer graphics, Java applet, web-based training

Additional information

ICGG 2002;　Journal of 10th ICGG, Vol.2, pp.172-177, 2002-8

"DEVELOPMENT FOR WEB-BASED CG SYSTEM AND ITS APPLICATION TO MODELING AND ANIMATION SYSTEMS"

by Yoshinori MOCHIZUKI, Tomoyuki NISHITA

Abstract

Network infrastructure has become an important topic in recent years, and there are now many different services using the World Wide Web. Accesses to Web contents from mobile terminals such as notebook PC's, cellular phones (i-mode, iappli) have increased. This paper proposes a Web-based CG system. Users specify parameters for the Web client using HTML FORM or Java Applets. The Web server receives these parameters, and executes a rendering process, which requires a high computational cost.We also apply this system to modeling and animation systems.

Key Words:

computer graphics, Java Applets, World Wide Web

Additional information

IEICE 2002;　Journal of IEICE, Vol.J85-D-II, No.6, pp.1047-1054, 2002

"The Development of 3D Graphics and VRML Libraries for Web3D Platform by Using Java"

by Bing-Yu Chen, Tomoyuki Nishita

Abstract

This paper proposes a new programming platform for 3D graphics on Web3D or Internet. To develop 3D graphics programs on Internet is not very easy, because there are no popular tools like OpenGL. For this purpose, we have developed a 3Dgraphics library, called jGL, by using pure Java. jGL is a general-purposed 3D graphics library, and its application programming interface is defined in a manner quite similar to that of OpenGL. Since jGL offers the same functionalities as OpenGL, the programmers could utilize it easily. Recently, people can use some simple Java programs on cellular phones, the migration testing toward iAPPLI will also be descript in this paper. Moreover, VRML (Virtual Reality Modeling Language) is a standard 3D graphics file format and very popular. To display a 3D model on Internet, people would like to use the VRML file format. Hence, we developed a VRML library, called jVL, by using pure Java and jGL.

Key Words:

OpenGL, VRML, Web3D, Java, Graphics Library

Additional information

Web3D 2002; 　Proc. of Web3D 2002, pp.35-42, 2002-2

"Multiresolution Streaming Mesh with Shape Preserving and QoS-like Controlling"

by Bing-Yu Chen, Tomoyuki Nishita

Abstract

How to transmit 3D meshes efficiently has become an important topic on Web3D platform, since there are more and more people need to use 3D models on the Internet. The data size of a geometric 3D model is usually large for being able to represent more details of the model, although we do not need to use such a detail model in most cases. Hence, to offer 3D model which shape and features could still be recognized easily with less data size is necessary. Additionally,the network bandwidth of the Internet is not stable actually, how much data is suitable for Internet is also a question. Therefore, we propose a new multiresolution streaming mesh for Internet transmission with QoS-like (Quality of Service) controlling in this paper. While transmitting the streaming mesh with our system, the server first deliversa simplified mesh model with the data size according to the current network bandwidth. If the user at the client side needs to use a more detail model, the server then sends some necessary patches to the client, so that the client program could show the detail model progressively. Our approach is different from previous works, for Web3D utilization, the size of the patch data which is used for reconstructing the original 3D model is less, and the shape and features of the simplified model could still be recognized easily. Moreover, ourmethod needs no complex computations, to generate this streaming mesh on demand is possible. With the QoS-like controlling, the transmission rate between the server and the client has been controlled automatically and the users could get the 3D models with proper qualities as their network situations.

Key Words:

Streaming Mesh, Mesh Simplification, Level of Detail, Geometric

Additional information

img
PG 2001; 　Proc. of Pacific Graphics 2001, p.374-383, 2001-10

"Efficient Rendering of Optical Effects within Water using Graphics Hardware,"

by Kei Iwasaki, Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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.

Key Words:

Water, Shafts of Light, Caustics, Shadows, Graphics Hardware, Natural Phenomena

Additional information

PG 2001;　 Proc. of Pacific Graphics2001, pp.363-372, 2001-10

"A Method for Modeling Clouds based on Atmospheric Fluid Dynamics"

by Ryou Miyazaki, Satoru Yoshida ,Yoshinori Dobashi, Tomoyuki Nishita

Abstract

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. This paper proposes a new method for modeling various kinds of clouds. The proposed method is based on the physical simulation of atmospheric fluid dynamics which characterizes the shape of clouds. To take account of the dynamics, we used a method called the coupled map lattice (CML). The coupled map lattice 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.

Key Words:

Clouds, natural phenomena, simulation, Coupled Map Lattice,
cellular automaton, metaballs

Additional information

PG 2001; 　Proc. of Pacific Graphics 2001, pp.390-399, 2001-10

"Efficient Rendering of Lightning Taking into Account Scattering Effects due to Cloud and Atmospheric Particles"

by Yoshinori Dobashi, Tsuyoshi Yamamoto, Tomoyuki Nishita

Abstract

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.

Key Words:

Lightning, Clouds, Atmospheric Scattering, Efficient Rendering,
Level of Detail, Graphics Hardware

Additional information
CADGraphics2001; 　Proc. of CAD & Graphics 2001, pp.333-343, 2001-8

"Animation Method for Pen-and-Ink Illustrations Using Stroke Cohenrency,"

by T.Haga, Henry Johan, Tomoyuki Nishita

Abstract

Pen-and-ink illustrations are attractive is that they have greater ability than photorealistic images to omit unimportant details,to clarify shapes and so on. Considering these advantages,we have created pen-and-ink-style animations.In our method, we treat 3D models as inputs and generate pen-and-ink-style line drawings in which the strokes of the illustration express the features of the original 3D geometry. In the illustrations generated,the density of strokes and the shapes of strokes represent the tone and the shape of the 3D models.If the models are moving/changing, we keep the coherence between the frames in order to generate smooth animations.For this purpose,the strokes are stored using a simple data structure that is able to retain the information in the previous frame.

Key Words:

pen-and-ink illustrations,line drawings,non-photorealistic rendering

Additional information
CGI2001; Proc. of Computer Graphics International 2001, pp.149-156, 2001-7

"Modeling and Rendering of Various Natural Phenomena Consisting of Particles"

by Tomoyuki Nishita, Yoshinori Dobashi

Abstract

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, flight 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 on sky, clouds, smoke, desert scenes and atmospheric effects, such as shafts of light. These phenomena have the common feature that they 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 very time-consuming. This paper describes efficient methods for creating realistic images of such natural phenomena.

Additional information
Web3D 2001; 　Proc. of Web3D 2001, pp.85-91, 2001-2

"jGL and its Applications as a Web3D Platform"

by Bing-Yu Chen, Tomoyuki Nishita

Abstract

This paper proposes a new platform for 3D graphics on the Internet (and recently also for Web3D). To develop 3D graphics programs on the Internet is not very easy, because there are no high-quality tools like OpenGL. For this purpose, we have developed a 3D graphics library, called jGL, by using pure Java since the end of 1996. At that time, we ignored some functions, such as texture mapping, because these functions were too complex to be realized on low-cost machines, even on the fastest machine three years ago. jGL is a general-purpose 3D graphics library, and its application-programming interface is defined in a manner quite similar to that of OpenGL. Today, the hardware is better, but the network bottleneck is still the same as before, so we almost re-wrote all the code to enhance its capabilities and performance and minimized its code size to make it more suitable for running on the Internet. Moreover, VRML is a standard 3D graphics file format and very popular. To display or play a 3D model or scene on the Internet, people would like to use the VRML file format, and use the VRML browser plug-in of the Internet browsers to view it. Unfortunately, besides the Microsoft Windows and SGI workstation environments, the support for displaying VRML models is not enough. Hence, we also developed a real platform independent VRML browser applet by using jGL, that can be used on any Java enabled Internet browsers. It is also a good example for jGL.

Key Words:

OpenGL, VRML, Web3D, Java

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PG2000; Proc. of Pacific Graphics2000 ,pp.348-358, 2000-10   

"Morphing Using Curves and Shape Interpolation Techniques"

by Henry Johan, Yuichi Koiso, T. Nishita

Abstract

This paper presents solutions to the feature correspondence and feature interpolation problems in image morphing. The user specifies the correspondence between the source and the target images by drawing input curves on the features of the objects. The correspondence between hese curves at the finest level (pixel level) is computed by optimizing a cost function. Based on this correspondence, the input curves are approximated by using Bezier curves. We represent the B´ ezier curves and the connections among them by using a dependency graph. Feature interpolation is performed by interpolating the dependency graphs using the edge-angle blending technique. We also propose methods for controlling the transition rates of the shape and the color. We implemented the proposed algorithms in our morphing system which is based on the field morphing technique. From experimental results, our algorithms can generate a smooth morphing animation even when the objects in the source and the target images have different orientations. Also, the user’s workload is reduced because the system includes an automatic feature correspondence computation.

Key Words:

Morphing, Shape Interpolation, Transition Control, Warping, Deformation, Animation.

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"Display Method of Smoke Flow Taking Obstacles into Account"

by Satoru Yoshida, T. Nishita

Abstract

Recently, displaying natural phenomena such as smoke has become a topic of interest in computer graphics. The ability to simulate the complex shapes and motion of the smoke particles is not only important but is also a difficult problem to solve. In this paper, we propose a method of displaying swirling smoke, including the consideration of its passage round obstacles. By using the idea of metaballs, we can easily represent the 3-dimensional density distribution of smoke. We solve the physical equation of the flow, and represent the vortices by using the vorticity vector. Therefore, we can make a model of the smoke flow even if there are obstacles in its path.

Key Words:

Smoke, Metaballs, Vorticity, Computational Fluid Dynamics, Natural Phenomena.

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PG 2000; Proc. of Pacific Graphics 2000, pp.427-430, 2000-10

"A Method for Modeling and Rendering Dunes with wind-ripples"

by Kouichi Onoue, T. Nishita

Abstract

This paper proposes a method for modeling and rendering realistic desert scenes. A desert terrain includes sand dunes and wind ripples.
We use two types of scale models to form them. We render the dunes with the wind-ripples by bump-mapping using LODs (Levels of Detail).

Key Words:

Natural phenomena, Dunes, Wind-ripples, Levels of Detail, Texture mapping, Bump mapping

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PG'99;　Proc. of Pacific Graphics 1999, pp.92-101, 1999-10

"A Scan Line Algorithm for Rendering Curved Tubular Objects"

by T. Nishita , H.Johan

Abstract

Parametric surfaces and implicit surfaces are generally used for representing curved surfaces in CAD/CG Systems. This paper discusses a curved tubular object (or generalized cylinder) which is a surface swept by a sphere/circle moving along a curve. For the trajectory curve, a 3D B\'{e}zier curve is employed, and its radius can be varied along the curve. In general, its surface cannot be defined by a closed form, while a high degree of polynomial must be solved for ray/surface intersection. This paper proposes an effective rendering method which uses a scan line algorithm for detecting curved tubular objects on the projection plane.
The calculation of the distance from a point to a curve plays an important role in our algorithm; Bezier Clipping Method is employed for this calculation.

Key Words:

Curved tubular objects, Swept volume, Bezier curve, Projection for curve, Closest point, Bezier Clipping

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PG'99; 　Proc. of Pacific Graphics 1999, pp.218-219, 1999-10

"Modeling and Rendering Methods of Clouds "

by T. Nishita , Y. Dobashi

Abstract

Recently, simulation of natural phenomena, such as water, smokes, fire, clouds, have been attempted in computer graphics. Clouds play an important role when generating images of outdoor scenes, the earth viewed from outer space and the visualization of weather information.
This paper describes the modeling methods of clouds, and an efficient calculation method for light scattering due to clouds taking into account both multiple scattering and sky light. The methods discussed here are also useful for displaying snow.

Key Words:

Clouds, multiple scattering, satelight image, metaballs, Fractal, natural phenomena, cellular automaton

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SMI99; Proc. of Shape Modeling International 99, pp.218-219, 1999-3

"Modeling and Deformation Method of Human Body Model Based on Range Data,"

by R. Matusda, T. Nishita

Abstract

A cloth simulation system must generate a human body model based on measured data obtained from range data. We propose modeling and deformation methods based on such data. In our system, the human body is modeled by layered metaballs which correspond to the horizontal cross section of the body. For each cross section, metaballs are generated by measured sample points on the boundary of the cross section. In order to fit the metaball surface with the sampling points, we employed the Steepest Descent method. For body deformation, the sampling points on the cross section are smoothly moved using Bezier curves. To show the effectiveness of the proposed method, we demonstrate fitting and deformation, the two human body models to be used for the cloth simulation.

Key Words:

dress simulation, metaball

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SCCG98; 　Proc. of SCCG98, pp.3-15, 1998-4

"Applications of Bezier Clipping Method and Their Java Applets,"

by T. Nishita

Abstract

Displaying objects with high accuracy is important in CAGD and for the synthesis of photo-realistic images. The representation of free-form surfaces can be classified into two: parametric surfaces such as Bezier patches, and implicit surfaces like metaballs. We discuss display methods for both Bezier patches and metaballs by using Bezier Clipping. Traditionally, polygonal approximation methods have been employed to display parametric surfaces. This paper introduces various display methods for Bezier patches without polygonal approximation. Bezier Clipping can be also applied to the following: 1) curve/curve intersection, 2) curve/surface intersection, 3) scan conversion of curved regions such as outline fonts, 4) various lighting simulations such as curved light sources and radiosity method. In order to show the effectiveness of Bezier Clipping widely by using the Internet, we have coded some of them(e.,g.,curve/curve intersection, metaballs) in Java language. The Bezier Clipping is very effective for displaying metaballs and metacircles (2D version of metaballs) and for the application of metaballs, we demonstrate realistic rendering of clouds, snow, smoke, and water droplets.

Additional information

Gazoudenshi 96; 　The Journal of Image and Electronics Society of Japan, Vol.24, No.3, pp.196-205,1995

"A Quick Rendering Method for Outdoor Scenes Using Sky Light Luminance Functions Expressed with Basis Functions,"

by Yoshinori Dobashi, Kazufumi Kaneda, Hideo Yamashita, Tomoyuki Nishita

Abstract

Recently, computer graphics has been often 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 design under various conditions by changing time in a day, seasons, or atmospheric conditions (clear or overcast sky). In traditional methods of calculating the illuminance due to sky light, however, all calculation must be performed from scratch if such conditions are changed. 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 method of quickly generating images of an outdoor scene by expressing the illuminance due to sky light with a series of basis functions, even if the luminous intensity distribution of the sky is changed.

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PG'96; 　Proc. of Pacific Graphics 1996, pp.117-132, 1996-8

"Display Method of the Sky Color Taking into Account Multiple Scattering"

by Tomoyuki Nishita, Yoshinori Dobashi, Kazufumi Kaneda, Hideo Yamashita

Abstract

Research on the rendering of natural scenes, such as clouds, ocean waves, trees, terrain, grass, and fire, has been growing very popular. This paper reports a shading model for sky color which is indispensable for natural scenes. In most cases, the sky color in outdoor scenes is blue in computer graphics for the sake of simplicity. However, the color of the sky is not simply blue. It changes according to viewing direction, the position of the sun, and conditions of the atmosphere. The sky plays an important role in architectural design and flight simulators. The color of the sky is determined by the scattering and absorption of air molecules, aerosols and other small particles in the atmosphere. In the previous method, only single scattering was taken into account for the sky color calculation. To display realistic images, multiple scattering can not be ignored.

This paper proposes two methods: a fast method to calculate the spectral distribution of sky radiation for single scattering, and an efficient method to calculate the sky color taking into account multiple scattering.

Key Words:

Sky color, Atmospheric scattering, Multiple scattering, Rayleigh scattering, Reflected light from the ground

Additional information

PG'96; 　Proc. of Pacific Graphics 1996, pp.66-79, 1996-8

"A Display System for Bezier Surfaces and Metaballs using Bezier Clipping"

by Tomoyuki Nishita

Abstract

Displaying objects with high accuracy is important in CAGD (Computer-Aided Geometric Design) and for the synthesis of photo-realistic images. The representation of free-form surfaces can be classified into two: parametric surfaces, such as Bezier patches and implicit surfaces, such as metaballs (or blobs). This paper discusses display methods for both Bezier patches and metaballs. Traditionally, polygonal approximation methods have been employed to display parametric surfaces. This paper introduces various display methods for trimmed Bezier patches without polygonal approximation by using raytracing, scanline algorithm, or hidden line elimination. In most display systems, parametric patches and Metaballs can not be displayed by a single program. In commercial software, to display both of them polygonization is used. This paper introduces a display system for both of them without polygonization. In our system, for hidden surface removal and shadow detection for both types of surfaces, the same idea, called Bezier Clipping, is employed. The Bezier Clipping can be also applied to various lighting simulations such as radiosity method.

Additional information

PG'96; 　Proc. of Pacific Graphics 1996, pp.50-65, 1996-8

"Animation of Water Droplet Flow on Curved surfaces"

by Kazufumi Kaneda, Y. Zuyama, Hideo Yamashita, Tomoyuki Nishita

Abstract

This paper proposes a method for generating a realistic animation of water droplets and their streams on curved surfaces, such as a windshield, taking into account the dynamics that act on the droplets. A water droplet runs down an inclined surface. The stram meanders down beacuse of impurities on the surface. Some amount of water remains behind because of the nature of the wetting phenomena. Therefore, the mass of the droplet decreases, and the droplet is decelerated as the result. Finally, the flow stops. In this paper, a discrete model of curved surfaces is debveloped to simulate the streams from the water droplets as described above. The urbed surface is divided into small meshes, and the flow of water droplets is calculated based on probability of movement. For rendering scenes to a wide variety of applications, we also develop two rendering mehods: a fast rendering method using a simplew model of water droplets and a high quality rendering mehotd that pursues the photo-reality. Animations of water droplets on a windshield or a teapot demonstrate the usefulness of the proposed method.

Keyword:

Animation, Water Droplet Flow, Curved Surface, Discrete Model, Dynamics

Additional information
PG'95; 　Proc. of Pacific Graphics 1995, pp.194-208, 1995

"A Fast Display Method of Sky Color using Basis functions"

by Yoshinori Dobashi, Kazufumi Kaneda, Hideo Yamashita, Tomoyuki Nishita

Abstract

Computer graphics recently have began 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 color 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, Legendre polynomials are used as basis functions. The sun altitude is altered at certain intervals and the distributions of the sky color for each sun altitude are pre-calculated and stored efficiently using Legendre polynomials. The color of the sky in the view direction for an arbitrary sun position can be obtained from the stored distributions and displayed quickly.

Additional information
CGI'93; 　Proc. of Computer Graphics International 1993, pp.244-257, 1993-6

"Display Algorithm of Brush Strokes using Bezier Functions"

by Tomoyuki Nishita, Shinichi Takita, and Eihachiro Nakamae

Abstract

Graphics editors have recently come into wide use. But for displaying high quality images, a more powerful tool has been desired. This paper proposes a useful display method for Chinese calligraphy, traditional Japanese ink painting called sumie, and watercolor painting. The method comprises techniques to express the outlines of a brush stroke and to vary shades of color. That is, the outlines of a brush stroke are modeled using piecewise Bezier curves, and the variation of gray shade inside of the outline are defined by Bezier functions. This method provides effective characteristics of a brush stroke such as shade variation, the scratchiness produced by dry brush, and blotchiness caused by the diffusion of ink.

Key Words:

Outline fonts, Bezier curves, Brush strokes, Chinese calligraphy, Scan conversion

Additional information

PG'93; 　Proc. of Pacific Graphics1993, pp.162-173, 1993

"METAMORPHOSIS USING BEZIER CLIPPING"

by TOMOYUKI NISHITA, TOSHIHISA FUJII, EIHACHIRO NAKAMAE

Abstract

Recently, in the field of entertainment, the metamorphosis of 2-D images, as it is an attractive technique, has come to be used in movies and television commercials. This technique is referred to as morphing. In the proposed method, Bezier or B-spline nets are overlapped onto digital images, and their deformation is performed by moving the control points of the nets on the images. The method proposed here has the following advantages: 1st order derivative continuity is preserved after deformation, any kind of affine transformation is available, and the nets are automatically set by extracting the contours of images.

Key Words:

Animation, Metamorphosis, Morphing, Free-form deformation

Additional information
CGI'92; 　Proc. of Computer Graphics International 1992, pp.429-445, 1992-6

"A Shading Model of Parallel Cylindrical Light Sources"

by Tomoyuki Nishita, Shinichi Takita, Eihachiro Nakamae

Abstract

In many industrial designs, such as automobiles and electrical products, evaluating the quality of curved surfaces in the design is very important. If the designer can confirm shapes of curved surfaces visually, working with photo-realistic computer generated images, the designer's ^^ ^^ sense'' is well utilized. In this paper we will demonstrate method for producing images which can be used by designers to evaluate the visual quality of free-form curved surfaces. The method uses the reflected images of cylindrical light sources. It is important that curved surfaces be displayed accurately, without polygonal approximation, and that the generated images be photo-realistic images, including shadows. The shading model presented in this paper satisfies these requirements.
Many offices, classrooms, and factories are lit with multiple fluorescent lamps arrayed in parallel rows on the ceiling. The shading technique presented in this paper is applicable to estimation of illuminance distribution in such an environment. Our method performs hidden surface removal and shadowing of curved surfaces without polygonal approximation, yielding accurate display.

Key Words:

Cylindrical light sources, quality of curved surfaces, shadows, penumbra, Bezier surfaces.

Additional information

CGI'90; 　Proc. of Computer Graphics International 1990, pp.493-506, 1990-6

"High-Quality Rendering of Parametric Surfaces by Using a Robust Scanline Algorithm"

by Tomoyuki Nishita, Kazufumi Kaneda, Eihachiro Nakamae

Abstract

Displaying objects with high accuracy is seriously required not only for CAGD (Computer Aided Geometric Design) but also for the synthesis of photo-realistic images. Traditionally, polygonal approximation methods have been employed to display curved surfaces. They bring on low accuracy of display not only in shape but also in intensity of objects. In this paper a scanline algorithm to directly display surface patches, expressed by Bezier surfaces, without polygonal approximation is proposed. In our proposal, curved surfaces are subdivided into subpatches with curved edges intersecting with a scanline, and the intersections of every subpatch and the scanline are calculated. This method is extremely robust for calculation of the intersections, which can be obtained with only a few iterations. Furthermore, the greater the number of patches, the more effective the method is regarding required memory and calculation time. Anti-aliased images with shadows and texture mapping are given to show the effectiveness of the method proposed.

Key Words:

Bezier Surfaces, Scanline algorithm, Robustness, High-quality rendering, Surface trimming, Silhouette detection, Shadowing

Additional information

CGI'92; 　Proc. of Computer Graphics International 1992, pp.595-619, 1992-6

"Hidden Curve Elimination of Trimmed Surfaces Using Bezier Clipping"

by Tomoyuki Nishita, Shinichi Takita, Eihachiro Nakamae

Abstract

Shaded display is popular for displaying curved surfaces because of the realistic appearance of the images produced. In the field of computer aided geometric design, however, line drawings are more commonly used. For accurate evaluation of the curved surfaces in these designs, the conventional method of approximating curved surfaces with polygons is insufficient. In this paper we will present a method of hidden line elimination without resorting to polygonal approximation. The method provides the designer smoother, more precise iso-parametric curves than traditional polygonal approximation methods. In addition, the method can draw precise silhouette curves, trimming curves, drawings of patterns represented by curves on the surface, and contour lines. Furthermore, the method is valid even for surfaces which penetrate each other.

Key Words:

Hidden curve elimination, Bezier clipping, extraction of silhouette, penetrated surfaces, contour lines, trimmed patch, curve-curve intersection.

Additional information

CGI'90; 　Proc. of Computer Graphics International 1990, pp.493-506, 1990-6

"High-Quality Rendering of Parametric Surfaces by Using a Robust Scanline Algorithm"

by Tomoyuki Nishita, K. Kaneda, Eihachiro Nakamae

Abstract

Displaying with high accuracy is seriously required not only for CAGD (Computer Aided Geometri Design) but also for the synthesis of photo-realistic images. Traditionally, polygonal approximation methods have been employed to display curved surfaces. They bring on low accuracy of display not only in shape but also in intensity of objects. In this paper a scanline algotithm to directly display surface patches, expressed by Bezier surfaces, without polygonal approximation is proposed. In our proposal, curved surfaces are subdivided into subpatches with curved edges intersecting with a scanline, and the intersections of every subpatch and the scanline are calculated. This method is extremely robust for calculation of the intersections, which can be obtained with only a few iterations. Furthermore, the greater the number of patches, the more effective the method is regarding required memory and calculation time. Anti-aliased images with shadows and texture mapping are given to show the effectiveness of the method proposed.

Keywords:

Bezier Surfaces, Scanline algotithm, Robustness, High-quality rendering,

Additional information

CGI'90; 　Proc. of Computer Graphics International 1990, pp.117-131, 1990-6

"Highly Realistic Visual Simulation of Outdoor Scene under Various Atmospheric Conditions"

by Kazufumi Kaneda, T. Okamoto, Eihachiro Nakamae, Tomoyuki Nishita

Abstract

A method for creating realistic images is proposed from the view point of displaying simulation results when designing a building in which various weater conditions are taken into account. So far, in order to create realistic images for interior design, the concept of readiosity as ambient light including spectral distribution has been debeloped. The method can display not only the brightness but also the hue and saturation of color. In contrast, for designing a building sky light has been treated as ambient light, in which the brightness under barious weather conditions could be calculated, but the influences on the hue and saturation of color were ignored. The proposed method creates realistic images considergin the brightness, hur and saturation under barious atmospheric conditions by taking into account the spectral distribution of both direct sunlight and sky light, Views of buildings including the influences of the particles in the atmosphere, i.e. clouds, fog, and beams, are useful for design not only of new buildings but also of new city areas.

Keywords:

Sky Lights, Specular Reflectance, Atmospheric Scattering Model, Visual Environment, Building Design

Additional information

CGI'89; 　Proc. of Computer Graphics International 1989, pp.633-647, 1989

"Reliability of Computer Graphics Images as Visual Assessment Tool"

by Eihachiro Nakamae, Kazufumi Kaneda, K. Miwa, Tomoyuki Nishita, Saeki

Abstract

This paper analyzes the use of computer graphics images as architectural assessment tool. The characteristics of such images as an architectural simulation tool are discussed and thir reliability as an assessment tool is evaluated and compared with that of traditional hand-generated perspective drawings. An example application, architectural simulation of a city renewal plan, is presented.

Keyword:

reliability, montage image, assessment, architectural simulation, computer graphcis system.

Additional information

IEE05; IEEE Computer Society Press, pp. 495-502, October, 2005

"A Feature-Driven Approach to Locating Optimal Viewpoints for Volume Visualization"

by Shigeo Takahashi , Issei Fujishiro, Yuriko Takeshima, and Tomoyuki Nishita

Abstract

Optimal viewpoint selection is an important task because it considerably influences the amount of information contained in the 2D projected images of 3D objects, and thus dominates their first impressions from a psychological point of view. Although several methods have been proposed that calculate the optimal positions of viewpoints especially for 3D surface meshes, none has been done for solid objects such as volumes. This paper presents a new method of locating such optimal viewpoints when visualizing volumes using direct volume rendering. The major idea behind our method is to decompose an entire volume into a set of feature components, and then find a globally optimal viewpoint by finding a compromise between locally optimal viewpoints for the components. As the feature components, the method employs interval volumes and their combinations that characterize the topological transitions of isosurfaces according to the scalar field. Furthermore, opacity transfer functions are also utilized to assign different weights to the decomposed components so that users can emphasize features of specific interest in the volumes. Several examples of volume datasets together with their optimal positions of viewpoints are exhibited in order to demonstrate that the method can effectively guide naive users to find optimal projections of volumes.

Keyword:

viewpoint selection, viewpoint entropy, direct volume rendering, interval volumes, level-set graphs

Additional information

IEE06; 　IEEE Transactions on Visualization and Computer Graphics, Vol. 12, No. 5, pp. 1141-1148, 2006.

"Occlusion-Free Animation of Driving Routes for Car Navigation Systems"

by Shigeo Takahashi , Kenichi Yoshida, Kenji Shimada, and Tomoyuki Nishita

Abstract

This paper presents a method for occlusion-free animation of geographical landmarks, and its application to a new type of car navigation system in which driving routes of interest are always visible. This is achieved by animating a nonperspective image where geographical landmarks such as mountain tops and roads are rendered as if they are seen from different viewpoints. The technical contribution of this paper lies in formulating the nonperspective terrain navigation as an inverse problem of continuously deforming a 3D terrain surface from the 2D screen arrangement of its associated geographical landmarks. The present approach provides a perceptually reasonable compromise between the navigation clarity and visual realism where the corresponding nonperspective view is fully augmented by assigning appropriate textures and shading effects to the terrain surface according to its geometry. An eye tracking experiment is conducted to prove that the present approach actually exhibits visually-pleasing navigation frames while users can clearly recognize the shape of the driving route without occlusion, together with the spatial configuration of geographical landmarks in its neighborhood.

Keyword:

car navigation systems, nonperspective projection, occlusion-free animation, visual perception, temporal coherence

Additional information