Three-Dimensional Shape from Shading: Perception and Mechanisms

[摘要] In this thesis, we address the issue of 3-D shape from shading by investigating shape perception in humans and the early vision mechanisms that subserve this perception. We first investigated the influence of scale, contour, and reflectance function on shape perception from shading. Our results suggest that subjects can form robust 3-D shape percepts that remain consistent across sittings for shapes of various contours and reflectance functions.We have found that salient 3-D percepts can be formed at the level of early vision mechanisms. Experiments in which a single target pattern is discriminated from multiple background distractors show that certain shaded, 2-D stimuli consistent with a top-lit, convex interpretation can be processed fast (<80 msec) and in parallel.Strong pop-out asymmetries and control experiments involving shaded patterns that do not have familiar 3-D interpretations suggest that such fast, parallel processing is indeed dependent upon perception of 3-D shape. We find that these mechanisms proceed most readily when the stimuli can be interpreted as convex and lit from top-left. These preferences for shape and lighting directions appear to be intrinsic to early vision and cannot be overturned using stereo disparity cues. These early vision 3-D mechanisms can also be influenced by 3-D contextual information.We report that, together with 3-D shape, apparent reflectance is computed fast as well.Moreover, it is apparent reflectance, rather than brightness or perceptual 3-D shape, that is the primary basis for discrimination during the early stages of visual processing.

[发布机构] University:California Institute of Technology;Department:Biology

[关键词] Biology