"A practical path guiding method for participating media" by Hong Deng, Beibei Wang et al.

Article Title

A practical path guiding method for participating media

Authors

Hong Deng, Nanjing University of Science and Technology, Nanjing 210094, China.
Beibei Wang, Nanjing University of Science and Technology, Nanjing 210094, China.
Rui Wang, State Key Lab of CAD&CG, Zhejiang University, Hangzhou 310058, China.
Nicolas Holzschuch, Univ. Grenoble-Alpes, Inria, CNRS, Grenoble INP, LJK, 38000 Grenoble, France.

Keywords

Monte Carlo, ray tracing, path guiding, volume light transport, participating media, rendering

Abstract

Rendering translucent materials is costly: light transport algorithms need to simulate a large number of scattering events inside the material before reaching convergence. The cost is especially high for materials with a large albedo or a small mean-free-path, where higher-order scattering effects dominate. In simple terms, the paths get lost in the medium. Path guiding has been proposed for surface rendering to make convergence faster by guiding the sampling process. In this paper, we introduce a path guiding solution for translucent materials. We learn an adaptive approximate representation of the radiance distribution in the volume and use it to sample the scattering direction, combining it with phase function sampling by resampled importance sampling. The proposed method significantly improves the performance of light transport simulation in participating media, especially for small lights and media with refractive boundaries. Our method can handle any homogeneous participating medium, with high or low scattering, with high or low absorption, and from isotropic to highly anisotropic.