Visual Computing Laboratory at Saitama University on Visual Computing Laboratory

Member

Mon, 01 Jan 0001 00:00:00 +0000

Faculty

Kei Iwasaki (Professor)
- google scholar
- DBLP
- ORCID
- keiiwasaki at acm.org
- kiwasaki at mail.saitama-u.ac.jp

D1

Xu Mingrui
Zhang Tingyu

M2

Tomoya Kozuki
Risa Matsuda
Hiroto Kaburagi
Koji Miura

M1

Asuka Hada
Eiji Sakai
Tomoyuki Miyauchi
Keiya Umehara

B4

Yuki Koyanagi
Kaito Sunouchi
Giichi Tamori
Kiyomi Tsukamoto
Haruma Yachi

Address

255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan.
Visual Computing Laboratory (VCL)
Graduate School of Science and Engineering
Saitama University

Access Map

Sat, 10 May 2025 00:00:00 +0000

Spherical Lighting with Spherical Harmonics Hessian

Abstract

In this paper, we introduce a second-order derivative of spherical harmonics, spherical harmonics Hessian, and solid spherical harmonics, a variant of spherical harmonics, to the computer graphics community. These mathematical tools are used to develop an analytical representation of the Hessian matrix of spherical harmonics coefficients for spherical lights. We apply our analytic representation of the Hessian matrix to grid-based SH lighting rendering applications with many spherical lights that store the incident light field as spherical harmonics coefficients and their spatial gradient at sparse grid. We develop a Hessian-based error metric, with which our method automatically and adaptively subdivides the grid whether the interpolation using the spatial gradient is appropriate. Our method can be easily incorporated into the grid-based precomputed radiance transfer (PRT) framework with small additional storage. We demonstrate that our adaptive grid subdivided by using the Hessian-based error metric can substantially improve the rendering quality in equal-time grid construction.

Paper

paper
supplemental document

Code

code generator for Spherical Harmonics Hessian via Solid Spherical Harmonics

Cite

@inproceedings{10.1145/3721238.3730689, author = {Iwasaki, Kei and Dobashi, Yoshinori}, title = {Spherical Lighting with Spherical Harmonics Hessian}, year = {2025}, isbn = {9798400715402}, publisher = {Association for Computing Machinery}, address = {New York, NY, USA}, url = {https://doi.org/10.1145/3721238.3730689}, doi = {10.1145/3721238.3730689}, abstract = {In this paper, we introduce a second-order derivative of spherical harmonics, spherical harmonics Hessian, and solid spherical harmonics, a variant of spherical harmonics, to the computer graphics community. These mathematical tools are used to develop an analytical representation of the Hessian matrix of spherical harmonics coefficients for spherical lights. We apply our analytic representation of the Hessian matrix to grid-based SH lighting rendering applications with many spherical lights that store the incident light field as spherical harmonics coefficients and their spatial gradient at sparse grid. We develop a Hessian-based error metric, with which our method automatically and adaptively subdivides the grid whether the interpolation using the spatial gradient is appropriate. Our method can be easily incorporated into the grid-based precomputed radiance transfer (PRT) framework with small additional storage. We demonstrate that our adaptive grid subdivided by using the Hessian-based error metric can substantially improve the rendering quality in equal-time grid construction.}, booktitle = {Proceedings of the Special Interest Group on Computer Graphics and Interactive Techniques Conference Conference Papers}, articleno = {33}, numpages = {10}, keywords = {Spherical Harmonics, Solid Spherical Harmonics, Spherical Harmonics Hessian, Spherical Light}, location = { }, series = {SIGGRAPH Conference Papers '25} }

Mon, 14 Oct 2024 00:00:00 +0000

Two-stage Resampling for Bidirectional Path Tracing with Multiple Light Sub-paths

Abstract

Recent advances in bidirectional path tracing (BPT) reveal that the use of multiple light sub-paths and the resampling of a small number of these can improve the efficiency of BPT. By increasing the number of pre-sampled light sub-paths, the possibility of generating light paths that provide large contributions can be better explored and this can alleviate the correlation of light paths due to the reuse of pre-sampled light sub-paths by all eye sub-paths. The increased number of pre-sampled light subpaths, however, also incurs a high computational cost. In this paper, we propose a two-stage resampling method for BPT to efficiently handle a large number of pre-sampled light sub-paths. We also derive a weighting function that can treat the changes in path probability due to the two-stage resampling. Our method can handle a two orders of magnitude larger number of presampled light sub-paths than previous methods in equal-time rendering, resulting in stable and better noise reduction than state-of-the-art methods.

Paper

paper
supplemental document

Cite

@article{https://doi.org/10.1111/cgf.14139, author = {Nabata, K. and Iwasaki, K. and Dobashi, Y.}, title = {Two-stage Resampling for Bidirectional Path Tracing with Multiple Light Sub-paths}, journal = {Computer Graphics Forum}, volume = {39}, number = {7}, pages = {219-230}, keywords = {CCS Concepts, • Computing methodologies → Computer graphics, Ray tracing}, doi = {https://doi.org/10.1111/cgf.14139}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/cgf.14139}, eprint = {https://onlinelibrary.wiley.com/doi/pdf/10.1111/cgf.14139}, abstract = {Abstract Recent advances in bidirectional path tracing (BPT) reveal that the use of multiple light sub-paths and the resampling of a small number of these can improve the efficiency of BPT. By increasing the number of pre-sampled light sub-paths, the possibility of generating light paths that provide large contributions can be better explored and this can alleviate the correlation of light paths due to the reuse of pre-sampled light sub-paths by all eye sub-paths. The increased number of pre-sampled light subpaths, however, also incurs a high computational cost. In this paper, we propose a two-stage resampling method for BPT to efficiently handle a large number of pre-sampled light sub-paths. We also derive a weighting function that can treat the changes in path probability due to the two-stage resampling. Our method can handle a two orders of magnitude larger number of presampled light sub-paths than previous methods in equal-time rendering, resulting in stable and better noise reduction than state-of-the-art methods.}, year = {2020} }

Mon, 14 Oct 2024 00:00:00 +0000

Efficient Visualization of Light Pollution for the Night Sky

Abstract

Artificial light sources make our daily life convenient, but cause a severe problem called light pollution. We propose a novel system for efficient visu- alization of light pollution in the night sky. Numerous methods have been proposed for rendering the sky, but most of these focus on rendering of the daytime or the sunset sky where the sun is the only, or dominant light source. For the visualization of the light pollution, however, we must consider many city light sources on the ground, resulting in excessive computational cost. We address this problem by precomputing a set of intensity distributions for the sky illuminated by city light at various locations and with different atmospheric conditions. We apply a principal component analysis and fast Fourier transform to the precomputed distributions, allowing us to efficiently visualize the extent of the light pollution. Using this method, we can achieve one to two orders of magnitudes faster computation compared to a naive approach that simply accumulates the scattered intensity for each viewing ray. Furthermore, the fast computation allows us to interactively solve the in- verse problem that determines the city light intensity needed to reduce light pollution. Our system provides the user with both a forward and inverse investigation tool for the study and minimization of light pollution.

Downloads

paper
supplemental document

Cite

@article{10.1145/3618337, author = {Dobashi, Yoshinori and Ishikawa, Naoto and Iwasaki, Kei}, title = {Efficient Visualization of Light Pollution for the Night Sky}, year = {2023}, issue_date = {December 2023}, publisher = {Association for Computing Machinery}, address = {New York, NY, USA}, volume = {42}, number = {6}, issn = {0730-0301}, url = {https://doi.org/10.1145/3618337}, doi = {10.1145/3618337}, journal = {ACM Trans. Graph.}, month = dec, articleno = {219}, numpages = {11}, keywords = {fast fourier transform, light pollution, principal component analysis, the night sky} }

Mon, 14 Oct 2024 00:00:00 +0000

Adaptive Irradiance Sampling for Many-Light Rendering of Subsurface Scattering

Abstract

Rendering a translucent material involves integrating the product of the transmittance-weighted irradiance and the BSSRDF over the surface of it. In previous methods, this spatial integral was computed by creating a dense distribution of discrete points over the surface or by importance-sampling based on the BSSRDF. Both of these approaches necessitate specifying the number of samples, which affects both the quality and the computation time for rendering. An insufficient number of samples leads to noise and artifacts in the rendered image and an excessive number results in a prohibitively long rendering time. In this article, we propose an error estimation method for translucent materials in a many-light rendering framework. Our adaptive sampling can automatically determine the number of samples so that the estimated relative error of each pixel intensity is less than a user-specified threshold. We also propose an efficient method to generate the sampling points that make large contributions to the pixel intensity taking into account the BSSRDF. This enables us to use a simple uniform sampling, instead of costly importance sampling based on the BSSRDF. The experimental results show that our method can accurately estimate the error. In addition, in comparison with the previous methods, our sampling method achieves better estimation accuracy in equal-time.

Paper

paper
supplemental document

Cite

@ARTICLE{9380921, author={Nabata, Kosuke and Iwasaki, Kei}, journal={IEEE Transactions on Visualization and Computer Graphics}, title={Adaptive Irradiance Sampling for Many-Light Rendering of Subsurface Scattering}, year={2022}, volume={28}, number={10}, pages={3324-3335}, keywords={Rendering (computer graphics);Scattering;Three-dimensional displays;Monte Carlo methods;Sampling methods;Error analysis;Tuning;Subsurface scattering;BSSRDF;adaptive sampling;many-lights}, doi={10.1109/TVCG.2021.3066640}}

RISBPT

Mon, 14 Oct 2024 00:00:00 +0000

Resampling-aware Weighting Functions for Bidirectional Path Tracing using Multiple Light Sub-paths

Abstract

Bidirectional path tracing (BPT) with multiple importance sampling (MIS) is a popular technique for rendering realistic images. Recently, it has been shown that BPT can be improved by preparing multiple light sub-paths and by resampling a small number of light sub-paths from them to generate full paths with large contribution. Traditionally, for MIS weights, the balance heuristic has widely been used to minimize the upper bound of variance, where each full path is weighted in proportion to the probability of the path. Although the probability of the path can change due to the resampling process, the weighting functions used in the previous methods remain unaf- fected by the change in probability, resulting in less efficiency. To address this problem, we propose new weighting functions for BPT with multiple light sub-paths. Our main contribution is a precise formulation of the vari- ance and the derivation of the weighting functions that can appropriately treat the change in probability. We demonstrate that our weighting functions significantly improve the image quality. We will release a simple version of our implementation as open source to ensure reproducibility.

Paper

paper
supplemental

Code

Cite

@article{10.1145/3338994, author = {Nabata, Kosuke and Iwasaki, Kei and Dobashi, Yoshinori}, title = {Resampling-aware Weighting Functions for Bidirectional Path Tracing Using Multiple Light Sub-Paths}, year = {2020}, issue_date = {April 2020}, publisher = {Association for Computing Machinery}, address = {New York, NY, USA}, volume = {39}, number = {2}, issn = {0730-0301}, url = {https://doi.org/10.1145/3338994}, doi = {10.1145/3338994}, journal = {ACM Trans. Graph.}, month = mar, articleno = {15}, numpages = {11}, keywords = {resampling importance sampling, multiple importance sampling, Bidirectional path tracing} }