Optical flow constraint equation extended to transparency

Motion transparency phenomena in image sequences are frequent but classical methods of motion estimation are unable to deal with them. This paper describes a method for estimating optical flow by a generalization of the brightness constancy assumption to additive transparencies. This assumption is based on three successive images of a sequence. Thus, by a development to its second order, we obtain an extension of the optical flow constraint equation. The approach assumes that motion is translational on a region large enough in order to regularize the aperture problem. In the way of avoiding outliers, due to a non respect of the brightness constancy assumption, a robust multi-resolution method is used. It is composed of a low-pass pyramid and a M-estimator technique. This method offers some good results on artificial and natural image sequences.