Conservative Radiance Interpolants for Ray Tracing

Abstract

Classical ray-tracing algorithms compute radiance returning to the eye along one or more sample rays through each pixel of an image. The output of a ray-tracing algorithm, although potentially photorealistic, is a two-dimensional quantity — an image array of radiance values — and is not directly useful from any viewpoint other than the one for which it was computed.

This paper makes several contributions. First, it directly incorporates the notion of radiometric error into classical ray-tracing, by lazy construction of conservative radiance interpolants in ray space. For any relative error tolerance ε, we show how to construct interpolants which return radiance values within ε of those that would be computed by classical (e.g., Whitted) ray-tracing. The second contribution of the paper is an explication of the four sources of aliasing inherent in classical ray tracing — termed gaps, blockers, funnels, and peaks — and an adaptive subdivision algorithm for identifying ray space regions guaranteed to be free of these phenomena. Finally, we describe a novel data structure that exploits object-space coherence in the radiance function to accelerate not only the generation of single images, but of image sequences arising from a smoothly varying sequence of eyepoints. We describe a preliminary implementation incorporating each of these ideas.