Spatial scale in stereo and shape from shading: image input, mechanisms, and tasks

The problem of spatial scale in depth perception can be considered at three stages: image input, mechanisms, and depth descriptors specific for certain tasks. A review is presented of a number of earlier experiments supporting the distinction between a coarse, correlation-based mechanism and a feature-matching mechanism of stereopsis in terms of their respective inputs and outputs. In order to measure the influence of the correlation mechanism on the perception of three-dimensional shape, a shape-probe experiment was designed. For smooth intensity profiles with constant disparity, the results show that perceived shape is largely independent of overall disparity but does make use of shape from shading as well as the assumption that brighter parts are in front (proximity-luminance covariance).