ABSTRACT
Global illumination algorithms try to simulate all light-transport mechanisms that contribute to an image. Path tracing is a conceptually simple, brute-force technique for computing the direct and indirect illumination in scenes with area light sources. Each ray is followed through the scene until it hits a light surface, the maximum recursion depth is reached, or the ray leaves the scene. The easiest type of scene to render with path tracing has an environment light as the only source of illumination. Part of the rationale is that the direct illumination varies rapidly, particularly in shadows, while the indirect illumination usually varies more slowly. A light-sampling approach for the direct illumination, will therefore result in less noise. Several techniques based on bidirectional path tracing are quite effective.
