Eric P. Lafortune and Yves D. Willems
Computer Graphics Forum, Special Issue on Rendering, Vol. 13, No. 2 (June '94), pp. 97-107.
In this paper we introduce the concept of the global reflection distribution function that allows to concisely formulate the global illumination problem. Unlike previous formulations it is not geared towards any specific algorithm. As an example of its versatility we derive a Monte Carlo rendering algorithm called bidirectional path tracing that seamlessly integrates the ideas of shooting and gathering power to create photorealistic images.
Scene rendered with bidirectional
path tracing (extended
with Eric Veach's
technique for combining estimators): one corner of our office by night,
rendered with `only' a 100 samples per pixel (640x480, 183 KBytes).
Corner of our office by day, rendered
with 500 samples per pixel (640x480, 240 KBytes).