Motion optimization of ordered blocks for overlapped block motion compensation

Abstract

While overlapped block motion compensation (OBMC) with block matching motion vectors yields better estimation accuracy than standard block matching, these estimates may be significantly improved by optimizing the motion vectors. Optimal motion vectors may be determined by an iterative and computationally intensive process. However, for a low-cost system (e.g., videoconferencing), such an approach is not feasible. An analysis of the compensation errors after motion optimization reveals that most gains in estimation accuracy result from the optimization of a fraction of the total number of blocks in a frame. It is thus conceivable that, by defining suitable ordering algorithms for blocks, coding systems could see improved performance by optimizing some number of blocks based on the ordering depending on available computational resources. With the aid of simulations we first show that most improvements by optimizing motion are limited to a few motion vectors. Then we present simple and intuitive algorithms based on compensation error after OBMC with block matching vectors to order blocks. Simulation results using these algorithms for ordering and optimizing motion are presented for two video sequences. The results reveal improvements obtained by optimizing the motion of the blocks from the ordering are reasonable; however, the improvements are not limited to the first fraction of blocks from the ordering, suggesting that better ordering algorithms be investigated in the future.