High Performance Hierarchical Block-based Motion Estimation for Real-Time Video Coding

Abstract

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 computing a coarse motion field calculated at the highest level of a multiresolution pyramid, and successively refining it. The preliminary estimation is performed by a full-search fixed-size block matching, whose computational load is low due to the reduced scale.At the successive levels, the initial field is updated by both increasing the spatial density and refining the vectors. In the areas where the approximation is satisfactory, the spatial sampling is left unchanged and only the vectors are updated; in the other areas, a higher number of vectors are used.A novel strategy to perform vector propagation and adaptive correction jointly has been implemented, which allows both an efficient level-to-level update of the motion field and an effective recovery from wrong estimations.The advantages of the proposed method are two-fold: firstly, 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 would not produce a significant improvement, thus achieving a lower computational load that makes it particularly suited to the implementation of real-time video codecs.