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.
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@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}
}