Summary: Backward Ray Tracing
Apollo Computer, Inc.
August, 1986 *
Ray tracing has become a very popular method for image synthesis due to its un
paralleled flexibility and its ability the generate images of high quality and realism.
Simulation of effects such as reflection and refraction have been the hallmarks of
ray tracing since its introduction . With the advent of stochastic ray tracing ,
the range of effects expanded to include motion blur, soft shadows, depth of field,
and both blurry reflections and translucency. A notable omission from the repertoire
of ray tracing, however, is diffuse reflection of indirect light. Though several new
algorithms have been introduced which simulate multiple diffuse reflections of light
in polygonal environments [1, 4], ray tracing continues to neglect these higher order
effects, and consequently falls short of a truly global model of illumination.
These notes describe a simple extension to ray tracing which takes a first step
toward alleviating this deficiency. The problem addressed is that of simulating diffuse
reflection of specularly reflected and/or refracted light originating from point light
sources. The technique involves one or more passes of backward ray tracing (from