DIRECT ESTIMATION OF FIRST ORDER OPTIC FLOW

Time to contact can be approximated from the divergence of the flow field. Direct differentiation of a measured flow field is not feasible in practice because of the ill-posedness of differentiation. We propose a group theoretical framework for direct determination of higher order flow fields. The basis is the invariance of the power spectrum of the Fourier transform to translations. By change of coordinate-system, invariance to other groups of actions can be constructed. Using this phase-based estimation the group element acting on the image can be recovered simply by taking inner products in the normal retinal coordinate system. The theory is applied to estimation of first order optic flow.