Steven Parker -
Peter Shirley -
University of Utah
A simple extension to ray tracing is presented that creates visually plausible ``soft'' shadows with little extra computation. Although these soft shadows are approximate, they are robust and have penumbra widths that behave in a believable way, including accurate placement of singularities where penumbra width is zero. The method has continuous behavior in space and time, so it is appropriate for both static and dynamic image generation.
A postscript version of the paper is available here.