Abstract

Shadow stereopsis is defined as the psychophysical phenomenon by which stereoscopic depth is perceived on the basis of shadows alone. It is impossible to judge the stereoscopic role of shadows by observing natural images because shadows are cast, and located, by edges that are themselves powerful stimuli for stereoscopic depth. Edges and shadows are inseparable. We isolate the role of shadows in stereo vision by means of a special technique that allows us to take stereo pictures in which all disparities, except those arising from shadows, are removed. These special stereo pairs (shadowgrams) present the same monocular view to each eye but preserve shadows as they would be seen by each eye in a natural, stereoscopic situation. The importance of shadows in stereo vision can be judged by observation of the presented shadowgrams. Shadows are a robust and powerful cue for depth perception. The same technique used to demonstrate the phenomenon of shadow stereopsis can be used to acquire anaglyph shadowgrams with a single camera and a very simple set-up consisting of a pair of light sources of complementary colors. We show many shadowgrams taken this way to corroborate the phenomenon and to demonstrate the potential of the technique.

© 1990 Optical Society of America