On Poisson solvers and semi-direct methods for computing area based optical flow

T. Simchony et al. (1990) proposed a semidirect method for computing area-based optical flow, based on the iterative application of a direct Poisson solver. This method is restricted to Dirichlet boundary conditions, i.e. it is applicable only when velocity vectors at the boundary of the domain are known a priori. It is shown, both experimentally and through analysis, that the semidirect method converges only for a very high degree of smoothness. At such levels of smoothness, the solution is obtained merely by filling in the known boundary values; the data from the image is almost totally ignored. It is concluded that the semidirect method is not suited for the computation of area-based optical flow