Scalable coding of variable size blocks motion vectors

In this paper we discuss an algorithm that is able to provide a scalable (multiresolution) representation of the motion field information. It has been recently demonstrated that, for an open loop wavelet video coder, it is possible to use at the decoder side a scaled version of the original motion information and the residual coefficients computed with the full resolution/quality motion field without incurring into drift. We propose a fully scalable wavelet based video coder that performs motion estimation-compensation in the wavelet domain. In particular the coding scheme is specifically designed for variable size block matching algorithms. In this scenario motion vectors are distributed across an irregular lattice according to a quadtree structure. The developed system allows a scalable representation of the motion field and a flexible allocation of the bit budget between motion and residual data. The simulations that we have carried out show, at low bit-rates, a significant gain of the proposed approach with respect to the case in which the motion information is coded lossless.