Hierarchical Light Sampling with Accurate Spherical Gaussian Lighting
SessionSampling and Light Transport
DescriptionImportance sampling using a light tree (i.e., a hierarchy of light clusters) has been widely used for many-light rendering. This technique samples a light source by stochastically traversing the tree according to the importance of each node. While this importance should be close to the illumination integral for each node's light cluster, it is infeasible to compute the exact solution. Therefore, existing methods used a rough approximation (e.g., upper bound), which results in significant Monte Carlo variance, especially for high-frequency microfacet BRDFs at grazing angles. In this paper, we present a more accurate approximation of the importance based on spherical Gaussians (SGs). Our method represents a light cluster with an SG light for each node, and analytically approximates the product integral of the SG light and a BRDF. Although high-quality SG lighting approximations have been studied, they could not be used for the node importance due to violations of an unbiased sampling constraint. To improve the sampling quality and satisfy the constraint for anisotropic microfacet BRDFs, we introduce a new high-quality SG lighting approximation by extending an NDF filtering method that has been used for specular antialiasing. For diffuse surfaces, we also present a simpler and more accurate SG lighting than the state-of-the-art SG approximation, satisfying the constraint. Using our method, we can efficiently reduce the Monte Carlo variance for many-light scenes with modern physically plausible materials.
Event Type
Technical Papers
TimeThursday, 5 December 20241:00pm - 1:11pm JST
LocationHall B5 (2), B Block, Level 5
