Dynamic Shading, Motion Parallax and Qualitative Shape
S. Waldon and C. R. Dyer, Proc. IEEE Workshop on Qualitative Vision, 1993, 61-70.

Abstract

We address the problem of qualitative shape recovery from moving surfaces. Our analysis is unique in that we consider specular inter-reflections and explore the effects of both motion parallax and changes in shading. To study this situation we define an image flow field called the reflection flow field, which describes the motion of reflection points and the motion of the surface. From a kinematic analysis, we show that the reflection flow is qualitatively different from the motion parallax because it is discontinuous at or near parabolic curves. We also show that when the gradient of the reflected image is strong, gradient-based flow measurement techniques approximate the reflection flow field and not the motion parallax. We conclude from these analyses that reliable qualitative shape information is generally available only at discontinuities in the image flow field.