Zero-crossing or feature-point based stereo algorithms can, by definition, determine explicit depth information only at particular points in the image. To compute a complete surface description, this sparse depth map must be interpolated. A computational theory of this interpolation or reconstruction process, based on a surface consistency constraint, has previously been proposed, implemented,
... [Show full abstract] and tested. In order to provide stronger boundary conditions for the interpolation process, other visual cues to surface shape are examined in this paper. In particular, it is shown that in theory, shading information from the two views can be used to determine the orientation of the surface normal along the feature-point contours, provided the photometric properties of the surface material are known. This computation can be performed by using a simple modification of existing photometric stereo algorithms. It is further shown that these photometric properties need not be known a priori, but can be computed directly from image irfadiance information for a particular class of surface materials. The numerical stability of the resulting equations is also examined.
