Models of light sources and illumination are fundamental in computer vision. Light sources have traditionally been modelled as objects that emit light, while illumination has been modelled as a radiance function defined over free space. The difficulty with traditional light source models is that, while a diverse collection of models exists, each is so specific that relationships between them, and between the algorithms based on them, are unclear. At the other extreme, models of spatial illumination have been so general that they have not provided sufficient constraint for vision. We seek to unify these two extremes by developing a ray-based computational model of light sources and illumination. The model articulates strong constraints on the geometry and radiance of light rays in a scene, and expresses the relationship between free space, sources, and illumination. This leads to an illumination square of natural illumination scenarios. Applications of this model to problems in computer vision are discussed.
M. Langer, S.W. Zucker