TY - CONF T1 - Relative depth from motion using normal flow: an active and purposive solution T2 - Proceedings of the IEEE Workshop on Visual Motion, 1991 Y1 - 1991 A1 - Huang, Liuqing A1 - Aloimonos, J. KW - 3D information KW - Automation KW - Computer vision KW - Educational institutions KW - Image motion analysis KW - image recognition KW - Image sequences KW - Laboratories KW - Layout KW - Motion analysis KW - Motion estimation KW - Nonlinear optics KW - normal flow KW - optic flow KW - Optical computing KW - Optical sensors KW - relative depth KW - retinal motion KW - spatiotemporal derivatives KW - time varying image intensity function KW - visual motion AB - The authors show how an active observer can compute the relative depth of (stationary or moving) objects in the field of view using only the spatiotemporal derivatives of the time varying image intensity function. The solution they propose is purposive in the sense that it solves only the relative depth from motion problem and cannot be used for other problems related to motion; active in the sense that the activity of the observer is essential for the solution of the problem. Results indicate that exact computation of retinal motion does not appear to be a necessary first step for some problems related to visual motion. In addition, optic flow, whose computation is an ill-posed problem, is related to the motion of the scene only under very restrictive assumptions. As a result, the use of optic flow in some quantitative motion analysis studies is questionable JA - Proceedings of the IEEE Workshop on Visual Motion, 1991 PB - IEEE SN - 0-8186-2153-2 M3 - 10.1109/WVM.1991.212807 ER -