Traditional stereo techniques determine range by relating two images of an object viewed from different directions. If the correspondence between picture elements is known, then distance to the object can be calculated by triangulation. Unfortunately, it is difficult to determine this correspondence. This paper introduces a novel technique called photometric stereo. The idea of photometric stereo is to vary the direction of the incident illumination between successive views while holding the viewing direction constant. This provides enough information to determine surface orientation at each picture element. Since the imaging geometry does not change, the correspondence between picture elements is known a priori. This stereo technique is photometric because it uses the intensity values recorded in a single picture element, in successive views, rather than the relative positions of features.
