Eric P. Lafortune and Yves D. Willems
Proceedings of the Winter School of Computer Graphics and Visualisation 95, Pilsen, Czech Republic (February 1995), pp. 384-392.
Bidirectional path tracing is a fairly new Monte Carlo algorithm for physically based rendering. Introduced as a generalisation of path tracing, the algorithm traces paths for each pixel, not only from the eye point but also from the light sources. It subsequently links the intersection points on the respective paths by means of shadow rays. Each shadow ray determines if a lighting contribution has to be added to the estimate of the radiance of the pixel.
In this paper we present a technique which reduces the number of shadow rays that are traced effectively. The resulting slight increase in the variance of the stochastic process can be undone by taking more samples. Practical tests show that the approach yields a reduction of the variance for the same amount of work.
This paper is available on-line as a gzip'ed Postscript file (9 pages, 117 KBytes, expands to 300 KBytes).