Bidirectional light transport with vertex merging

Abstract

We present vertex merging -- a bidirectional path sampling technique for Monte Carlo light transport integration. Vertex merging is simple and more computationally efficient for specular-diffuse-specular effects than the currently available techniques in bidirectional path tracing. It brings the advantages of photon mapping to the path integral framework, while avoiding the concept of density estimation altogether. This makes it possible for the first time to quantitatively reason about the efficiency of two rendering approaches that have been historically considered conceptually different. The practical result is a combined bidirectional rendering algorithm that efficiently handles a wide variety of lighting conditions, ranging from direct illumination and diffuse inter-reflections to the notoriously problematic reflected caustics. This algorithm also has a higher order of convergence than progressive photon mapping.