HIGH-PERFORMANCE HIERARCHICAL BLOCK-BASED MOTION ESTIMATION FOR REAL-TIME VIDEO CODING

The paper addresses the problem of block-based motion estimation (BBME ) for video sequence coding, and a hierarchical strategy that sharply reduces the computation is proposed. Estimation is performed by comput ing a coarse motion held calculated at the highest level of a multires olution pyramid, and successively refining it. The preliminary estimat ion is performed by a full-search fixed-size block matching, whose com putational load is low due to the reduced scale. At the successive lev els, the initial field is updated by both increasing the spatial densi ty and refining the vectors. In the areas where the approximation is s atisfactory, the spatial sampling is left unchanged and only the vecto rs are updated; in the other areas, a higher number of vectors are use d. A novel strategy to perform vector propagation and adaptive correct ion jointly has been implemented, which allows both an efficient level -to-level update of the motion field and an effective recovery from wr ong estimations. The advantages of the proposed method are two-fold: f irstly, it produces a motion field whose density is locally adaptive, thus allowing the transmission of a smaller number of motion vectors. Moreover, it reduces the BBME task when a more detailed estimation wou ld not produce a significant improvement, thus achieving a lower compu tational load that makes it particularly suited to the implementation of realtime video codecs. (C) 1998 Academic Press Limited.