Backward Ray Tracing

Ray tracing has become a very popular method for image synthesis due to its un paralleled exibility and its ability the generate images of high quality and realism Simulation of e ects such as re ection and refraction have been the hallmarks of ray tracing since its introduction With the advent of stochastic ray tracing the range of e ects expanded to include motion blur soft shadows depth of eld and both blurry re ections and translucency A notable omission from the repertoire of ray tracing however is di use re ection of indirect light Though several new algorithms have been introduced which simulate multiple di use re ections of light in polygonal environments ray tracing continues to neglect these higher order e ects and consequently falls short of a truly global model of illumination These notes describe a simple extension to ray tracing which takes a rst step toward alleviating this de ciency The problem addressed is that of simulating di use re ection of specularly re ected and or refracted light originating from point light sources The technique involves one or more passes of backward ray tracing from the light and the construction of illumination maps as a pre processing step