Unbiased Emission and Scattering Importance Sampling For Heterogeneous Volumes

We present two new distance-sampling methods for production volume path tracing. We extend the null-collision integral formulation to efficiently gather heterogeneous volumetric emission, achieving higher-quality results. Additionally, we propose a tabulation-based approach to importance sample volumetric in-scattering through a spatial guiding data structure. Our methods improve the sampling efficiency for scenarios where low-order heterogeneous scattering dominates, which tends to cause high variance renderings with existing null-collision methods.