Liou and Jain 1987 : An analysis of existing motion detectors for determining desirable characteristics of a motion detector is presented. A gradient-based spatiotemporal model is then proposed for motion detection. Mathematical analysis of this model gives conditions under which the motion constraint equation is valid. The local motion information, obtained from the parameters of the Monge patch approximating the intensity hypersurface in the spatiotemporal space, may be used for segmentation of dynamic scenes. Motion detection results for real sequences show the robustness of the detector.