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UEI Research

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Nabata K.,Wakayama University | Iwasaki K.,Wakayama University | Iwasaki K.,UEI Research | Dobashi Y.,Hokkaido University | And 3 more authors.
Computer Graphics Forum | Year: 2016

The popularity of many-light rendering, which converts complex global illumination computations into a simple sum of the illumination from virtual point lights (VPLs), for predictive rendering has increased in recent years. A huge number of VPLs are usually required for predictive rendering at the cost of extensive computational time. While previous methods can achieve significant speedup by clustering VPLs, none of these previous methods can estimate the total errors due to clustering. This drawback imposes on users tedious trial and error processes to obtain rendered images with reliable accuracy. In this paper, we propose an error estimation framework for many-light rendering. Our method transforms VPL clustering into stratified sampling combined with confidence intervals, which enables the user to estimate the error due to clustering without the costly computing required to sum the illumination from all the VPLs. Our estimation framework is capable of handling arbitrary BRDFs and is accelerated by using visibility caching, both of which make our method more practical. The experimental results demonstrate that our method can estimate the error much more accurately than the previous clustering method. © 2016 The Author(s) Computer Graphics Forum © 2016 The Eurographics Association and John Wiley & Sons Ltd. Published by John Wiley & Sons Ltd.

Sato S.,UEI Research | Dobashi Y.,Hokkaido University | Yue Y.,Columbia University | Iwasaki K.,Wakayama University | Nishita T.,Hiroshima Shudo University
Visual Computer | Year: 2015

Physically based fluid simulations usually require expensive computation cost for creating realistic animations. We present a technique that allows the user to create various fluid animations from an input fluid animation sequence, without the need for repeatedly performing simulations. Our system allows the user to deform the flow field in order to edit the overall fluid behavior. In order to maintain plausible physical behavior, we ensure the incompressibility to guarantee the mass conservation. We use a vector potential for representing the flow fields to realize such incompressibility-preserving deformations. Our method first computes (time-varying) vector potentials from the input velocity field sequence. Then, the user deforms the vector potential, and the system computes the deformed velocity field by taking the curl operator on the vector potential. The incompressibility is thus obtained by construction. We show various examples to demonstrate the usefulness of our method. © 2015, Springer-Verlag Berlin Heidelberg.

Iwasaki K.,Wakayama University | Iwasaki K.,UEI Research | Mizutani K.,Wakayama University | Dobasbi Y.,Hokkaido University | And 3 more authors.
Computer Graphics Forum | Year: 2014

This paper proposes an interactive rendering method of cloth fabrics under environment lighting. The outgoing radiance from cloth fabrics in the microcylinder model is calculated by integrating the product of the distant environment lighting, the visibility function, the weighting function that includes shadowing/masking effects of threads, and the light scattering function of threads. The radiance calculation at each shading point of the cloth fabrics is simplified to a linear combination of triple product integrals of two circular Gaussians and the visibility function, multiplied by precomputed spherical Gaussian convolutions of the weighting function. We propose an efficient calculation method of the triple product of two circular Gaussians and the visibility function by using the gradient of signed distance function to the visibility boundary where the binary visibility changes in the angular domain of the hemisphere. Our GPU implementation enables interactive rendering of static cloth fabrics with dynamic viewpoints and lighting. In addition, interactive editing of parameters for the scattering function (e.g. thread's albedo) that controls the visual appearances of cloth fabrics can be achieved. © 2014 The Author(s) Computer Graphics Forum © 2014 The Eurographics Association and John Wiley & Sons Ltd. Published by John Wiley & Sons Ltd.

Huang C.-C.,National Taiwan University | Liang R.-H.,National Taiwan University | Liang R.-H.,Academia Sinica, Taiwan | Chan L.,National Taiwan University | And 2 more authors.
ACM SIGGRAPH 2014 Emerging Technologies, SIGGRAPH 2014 | Year: 2014

Hand tracking technologies allow users to control a remote display freely. The most prominent freehand remote controlling method is through a body-centric cursor, e.g. Kinect. Using that method, a user can first place the cursor to a rough position on the remote display, move the cursor to the exact position, and then commit the selection by a gesture. Although controlling the body-centric cursor is intuitive, it is not efficient for novel users who are not familiar with their proprioception. Inaccurate cursor placement results in long dragging movement, and therefore causes consequent arm fatigue problems. © 2014 held by the Owner/Author.

Kanazawa K.,University of Tokyo | Tanabe R.,Tokyo Denki University | Moriya T.,Tokyo Denki University | Takahashi T.,Tokyo Denki University | Takahashi T.,UEI Research
ACM SIGGRAPH 2015 Posters, SIGGRAPH 2015 | Year: 2015

Realistic representation of nature scenes is one of the most challenging areas in computer graphics community. There are important factors to synthesize realistic scenes in 3D CG which are decayed materials such as dead trees, weathered statues, rusty metals and so on. We are interested in the methodology for simulating its decaying processes. In this paper, we propose a simple method for rust aging simulation based on a probabilistic cellular automaton model taking into account object's geometries.

Kanazawa K.,University of Tokyo | Kanazawa K.,Tokyo Denki University | Sakato Y.,Tokyo Denki University | Takahashi T.,Tokyo Denki University | Takahashi T.,UEI Research
ACM SIGGRAPH 2013 Talks, SIGGRAPH 2013 | Year: 2013

To generate realistic representation of the nature scene is one of the most challenging areas in the computer graphics community. Ray tracing[1] is the most well-known technique to synthesize a realistic image. Since ray tracing is the most suitable method for simulating reflection and refraction of the light, it has been used for simulating atmospheric optical phenomena due to reflection and refraction of the light. The mirage is a kind of atmospheric optical phenomenon. Therefore, it is possible to synthesize mirages in 3DCG by simulating or modeling condition of the air. We focus on pencil tracing technique[2] that is an extention of conventional ray tracing technique based on the paraxial approximation theory. Our simple method based on pencil tracing can efficiently generate an appearance of mirage without any complex thermodynamic simulation.

Susaki M.,Tokyo Denki University | Sunagawa S.,Tokyo Denki University | Moriya T.,Tokyo Denki University | Takahashi T.,Tokyo Denki University | Takahashi T.,UEI Research
ACM SIGGRAPH 2013 Posters, SIGGRAPH 2013 | Year: 2013

There are a lot of people who have had yearning for conducting orchestra. It must be a very pleasant experience to coordinate orchestra performance with your own conduct, but it requires a vast amount of money. With such needs, there have been researches to simulate the situation of conducting orchestra by using gesture recognition [Usa][Baba][Sunagawa]. But, they do not generate performance scenes.

Takahashi T.,University of North Carolina at Chapel Hill | Takahashi T.,UEI Research | Dobashi Y.,UEI Research | Dobashi Y.,Hokkaido University | And 4 more authors.
Computer Graphics Forum | Year: 2015

We propose a stable and efficient particle-based method for simulating highly viscous fluids that can generate coiling and buckling phenomena and handle variable viscosity. In contrast to previous methods that use explicit integration, our method uses an implicit formulation to improve the robustness of viscosity integration, therefore enabling use of larger time steps and higher viscosities. We use Smoothed Particle Hydrodynamics to solve the full form of viscosity, constructing a sparse linear system with a symmetric positive definite matrix, while exploiting the variational principle that automatically enforces the boundary condition on free surfaces. We also propose a new method for extracting coefficients of the matrix contributed by second-ring neighbor particles to efficiently solve the linear system using a conjugate gradient solver. Several examples demonstrate the robustness and efficiency of our implicit formulation over previous methods and illustrate the versatility of our method. © 2015 The Author(s) Computer Graphics Forum © 2015 The Eurographics Association and John Wiley & Sons Ltd. Published by John Wiley & Sons Ltd.

Takahashi T.,Keio University | Takahashi T.,UEI Research | Nishita T.,UEI Research | Nishita T.,Hiroshima Shudo University | Fujishiro I.,Keio University
Computers and Graphics (Pergamon) | Year: 2014

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. © 2014 Elsevier Ltd.

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