Illumination distribution from shadows

The image irradiance of a three-dimensional object is known to be the function of three components: the distribution of light sources, the shape, and reflectance of a real object surface. In the past, recovering the shape and reflectance of an object surface from the recorded image brightness has been intensively investigated. On the other hand, there has been little progress in recovering illumination from the knowledge of the shape and reflectance of a real object. In this paper, we propose a new method for estimating the illumination distribution of a real scene from image brightness observed on a real object surface in that scene. More specifically, we recover the illumination distribution of the scene from a radiance distribution inside shadows cast by an object of known shape onto another object surface of known shape and reflectance. By using the occlusion information of the incoming light, we are able to reliably estimate the illumination distribution of a real scene, even in a complex illumination environment.