Exploiting reflectance properties to analyze images of moving objects needs local constraints

Dreschler and Nagel and Westphal and Nagel describe a system, which derives polyhedral object descriptions of moving rigid objects from monocular image sequences. In order to explore the possibilities to improve such a non-convex polyhedral object description into one with curved surface patches, the systematic gray value variations in a series of corresponding locations within the images of a moving object are investigated. Conditions are stated for a non-linear approach which estimates the local surface normal and albedo. It is proven that the constraints induced by the temporal gray value variations are not sufficient in real outdoor scenes.