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arXiv · 2109.14398

Position-free Multiple-bounce Computations for Smith Microfacet BSDFs

Beibei Wang·Wenhua Jin·Jiahui Fan·Jian Yang·Nicolas Holzschuch·Ling-Qi Yan
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Abstract

Bidirectional Scattering Distribution Functions (BSDFs) encode how a material reflects or transmits the incoming light. The most commonly used model is the Microfacet BSDF. It computes material response from the micro-geometry of the surface assuming a single bounce on specular microfacets. The original model ignores multiple bounces on the micro-geometry, resulting in energy loss, especially with large roughness. In this paper, we present a position-free formulation of multiple bounces inside the micro-geometry, which eliminates this energy loss. We use an explicit mathematical definition of path space that describes single and multiple bounces in a uniform way. We then study the behavior of light on the different vertices and segments in path space, leading to an accurate and reciprocal multiple-bounce description of BSDFs. We also present practical, unbiased Monte-Carlo estimators to compute multiple scattering. Our method is less noisy than existing algorithms for computing multiple scattering. It is almost noise-free with a very-low sampling rate, from 2 to 4 samples per pixel.

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Beibei Wang, Wenhua Jin, Jiahui Fan, Jian Yang, Nicolas Holzschuch, Ling-Qi Yan. 2021-09-29. Position-free Multiple-bounce Computations for Smith Microfacet BSDFs. https://arxiv.org/abs/2109.14398

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