Multiple Vertex Next Event Estimation for Lighting in dense, forward‐scattering Media

• Published in: Computer graphics forum Vol. 36; no. 2; pp. 21 - 30
• Main Authors: Weber, Pascal, Hanika, Johannes, Dachsbacher, Carsten
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.05.2017
• Subjects: Categories and Subject Descriptors (according to ACM CCS); Forward scattering; I.3.7 [Computer Graphics]: Three Dimensional Graphics and Realism—Raytracing; Importance sampling; Light sources; Lighting; Monte Carlo simulation; Random walk; Segments
• ISSN: 0167-7055; 1467-8659
• DOI: 10.1111/cgf.13103

We present a new technique called Multiple Vertex Next Event Estimation, which outperforms current direct lighting techniques in forward scattering, optically dense media with the Henyey‐Greenstein phase function. Instead of a one‐segment connection from a vertex within the medium to the light source, an entire sub path of arbitrary length can be created and we show experimentally that 4–10 segments work best in practice. This is done by perturbing a seed path within the Monte Carlo context. Our technique was integrated in a Monte Carlo renderer, combining random walk path tracing with multiple vertex next event estimation via multiple importance sampling for an unbiased result. We evaluate this new technique against standard next event estimation and show that it significantly reduces noise and increases performance of multiple scattering renderings in highly anisotropic, optically dense media. Additionally, we discuss multiple light sources and performance implications of memory‐heavy heterogeneous media.