Zero-crossing or feature-point based stereo algorithms can, by definition, determine explicit depth information only at particular points on 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. 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 principle, shading information from the two views can be used to determine the orientation of the surface normal along the feature-point contours, as well as the parameters of the reflective properties of the surface material. The numerical stability of the resulting equations is also examined.
