Dynamic Shading, Motion Parallax and Qualitative Shape

W e address the problem of qualitative shape recovery f rom moving surfaces. Our analysis is unique an that we consider specular interreflections and explore the effects of both motion parallax and changes an shading. To study this si tuation we define an image flow field called the reflection flow field, which describes the motion of reflection points and the mot ion of the surface. From a kinematic analysis, we show that the reflection f low i s qualitatively different f rom the motion parallax because i t is discontinuous at or near parabolic curves. W e also show that when the gradient of the reflected image is strong, gradientbased f low measurement techniques approximate the reflection flow field and not the motion parallax. W e conclude f rom these analyses that reliable qualitative shape information i s generally available only at discontinuities in the image f low field.