A unified framework for scene illuminant estimation

Most existing illuminant estimation algorithms work with assumptions of specific source types (e.g. directional light source or point light source). The assumptions bring up two main limitations which significantly restrict their applicabilities: first, the prior knowledge about source types is needed; second, it can not handle complex scenes where multiple source types co-exist. In this paper, we develop a general light source model which is designed to model arbitrary light sources. With the general source model, we are able to estimate multiple illuminants of different types within a single unified framework. We use a plastic sphere to probe both diffuse and specular reflections of a scene. With specular reflections, we estimate geometric parameters of the illuminants by a novel ray tracing and matching algorithm. The diffuse reflections are used to estimate photometric parameters of the illuminants. We also notice that common source types are degenerate cases of the general source model under certain conditions. Therefore, we can approximate light sources with common source types by checking the conditions. The approximations serve as type determinations of light sources, which makes our framework extremely useful for lighting related algorithms which need prior knowledge about light sources. Experiment results on a variety of real images demonstrate the efficiency and accuracy of our algorithm.