Shape and source from shading using zero crossings

Proposes a new estimation method of 3D shape of an object and the illuminant direction from a single image using the zero crossings under the assumption that the illuminant direction and strength, and the object surface albado are unknown. In most practical cases the illuminant direction is unknown. For these cases, a new theory was proposed by M.J. Brooks and B.K.P. Horn (1985) where the illuminant direction and 3D shape are simultaneously estimated from a single image. This theory, however, can not be applied to an object whose surface is not convex. The authors propose a new theory which has no such drawback