Virtual Ray Lights for Rendering Scenes with Participating Media

 

We present an efficient many-light algorithm for simulating indirect illumination in, and from, participating media. Instead of creating discrete virtual point lights (VPLs) at vertices of random-walk paths, we present a continuous generalization that places virtual ray lights (VRLs) along each path segment in the medium.

August 5, 2012
ACM SIGGRAPH 2012

 

Authors

Jan Novák (Disney Research/Karlsruhe Institute of Technology)

Derek Nowrouzezahrai (Disney Research/Université de Montréal)

Carsten Dachsbacher (Karlsruhe Institute of Technology)

Wojciech Jarosz (Disney Research)

Virtual Ray Lights for Rendering Scenes with Participating Media

Abstract

We present an efficient many-light algorithm for simulating indirect illumination in, and from, participating media. Instead of creating discrete virtual point lights (VPLs) at vertices of random-walk paths, we present a continuous generalization that places virtual ray lights (VRLs) along each path segment in the medium. Furthermore, instead of evaluating the lighting independently at discrete points in the medium, we calculate the contribution of each VRL to entire camera rays through the medium using an efficient Monte Carlo product sampling technique. We prove that by spreading the energy of virtual lights along both light and camera rays, the singularities that typically plague VPL methods are significantly diminished. This greatly reduces the need to clamp energy contributions in the medium, leading to robust and unbiased volumetric lighting not possible with current many-light techniques. Furthermore, by acting as a form of final gather, we obtain higher-quality multiple-scattering than existing density estimation techniques like progressive photon beams.

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