William T. Reeves, David H. Salesin, Robert L. Cook
We present a solution to the aliasing problem for shadow algorithms that use
depth maps. The solution is based on a new filtering technique called percentage
closer filtering. In addition to antialiasing, the improved algorithm provides
soft shadow boundaries that resemble penumbrae. We describe the new algorithm
in detail, demonstrate the effects of its parameters, and analysze its performance.
Available in the Proceedings of SIGGRAPH 1987.