The orientation of patches on the surface of an object can be determined from multiple images taken with different illuminations, but from the same viewing position. This method, referred to as photometric stereo, can be implemented using table lookup based on numerical inversion of experimentally determined reflectance maps. Here we concentrate on objects with specularly reflecting surfaces, since these are of importance in industrial applications. Previous methods, intended for diffusely reflecting surfaces, employed point source illumination, which is quite unsuitable in this case. Instead, we use a distributed light source obtained by uneven illumination of a diffusely reflecting planar surface. Experimental results are shown to verify analytic expressions obtained for a method employing three light source distributions.
