Efficient Image-Based Methods for Rendering Soft Shadows
We present two efficient image-based approaches for computation and display of high-quality soft shadows from area light sources. Our methods are related to shadow maps and provide the associated benefits. The computation time and memory requirements for adding soft shadows to an image depend on image size and the number of lights, not geometric scene complexity. We also show that because area light sources are localized in space, soft shadow computations are particularly well suited to image-based rendering techniques. Our first approach---layered attenuation maps---achieves interactive rendering rates, but limits sampling flexibility, while our second method---coherence-based raytracing---of depth images, is not interactive, but removes the limitations on sampling and yields high quality images at a fraction of the cost of conventional raytracers. Combining the two algorithms allows for rapid previewing followed by efficient high-quality rendering.
Maneesh Agrawala, Ravi Ramamoorthi, Alan Heirich, and Laurent Moll. "Efficient Image-Based Methods for Rendering Soft Shadows". In SIGGRAPH '00, pages 375–384, 2000.