Thomas Porter, Tom Duff
Most computer graphics pictures have been computed all at once, so that
the rendering program takes care of all computations relating to the overlap
of objects. There are several applications, however, where elements must be
rendered separately, relying on compositing techniques for the anti-aliased
accumulation of the full image. This paper presents the case for four-channel
pictures, demonstrating that a matte component can be computed similarly to
the color channels. The paper discusses guidelines for the generation of
elements and the arithmetic for their arbitrary compositing.
Available in the Proceedings of SIGGRAPH 1984.