Spatially Varying Illumination: A Computational Model of Converging and Diverging Sources

There are three reasons for illumination to vary within a scene. First, a light source may be visible from some surfaces but not from others. Second, because of linear perspective, the shape and size of a finite source may be different when viewed from different points in a scene. Third, the brightness of a source may be non-uniform. These variations are captured by a new computational model of spatially varying illumination. Two types of source are described: a distant hemispheric source such as the sky in which light converges onto a scene, and a proximal source such as a lamp in which light diverges into a scene. Either type of source may have a non-uniform brightness function. We show how to render surfaces using this model, and how to compute shape from shading under it.