ON POISSON SOLVERS AND SEMIDIRECT METHODS FOR COMPUTING AREA BASED OPTICAL-FLOW

Simchony, Chellappa, and Shao [1] recently proposed a semi-direct meth od for computing area based optical flow. Their method is based on the iterative application of a direct Poisson solver. This method is rest ricted to Dirichlet boundary conditions, i.e., it is applicable only w hen velocity vectors at the boundary of the domain are known a priori. We show, both experimentally and through analysis, that the semi-dire ct method converges only for very large smoothness. At such revels of smoothness, the solution is obtained merely by filling in the known bo undary values; the data from the image is almost totally ignored. Next , we consider the Concus and Golub method [2], another semi-direct met hod, for computing optical flow. This method always converges, but the convergence is too slow to be of any practical value. We conclude tha t semi-direct methods are not suited for the computation of area based optical flow.