Abstract

Since the time of Leonardo Da Vinci there has been very little research on how human observers perceive shape from shading. Our experiments suggest that shading is a primitive visual dimension that is extracted relatively early in visual processing. More recently, our research has focused on the question of how information about shading interacts with other visual functions such as motion, occlusion, stereopsis, symmetry, and perceptual grouping. We find that (1) In extracting shape from shading the visual system incorporates the single light source constraint; i.e., it assumes that there is only one light source illuminating most of the image. This is especially true for different parts of a single object. (The rule can sometimes be overridden for multiple objects.) (2) Tokens defined by shading can be used for perceptual grouping and segregation. (3) Occlusion boundaries (e.g., illusory contours) strongly influence the extraction of shape from shading. Chromatic borders, on the other hand, are completely ineffective. (4) Shading can provide an input to motion perception.

© 1989 Optical Society of America