Fast DCT domain inverse motion compensation algorithm based on shared information in a macroblock

Abstract

The ability to construct intra-coded frame from motion-compensated inter-frame coded directly in the compressed domain is important for efficient video manipulation and composition. In the context of motion-compensated DCT-based coding of video as in MPEG video, this problem of DCT domain inverse motion compensation has been studied in [1] and fast algorithm based on factorization of the DCT matrix is proposed in [2]. These schemes, however, treat each 8×8 block as a fundamental unit, and do not take into account the fact that in MPEG, a macrolock consists of several such blocks. In this paper, we show how shared information within a macroblock such as motion vector and common blocks can be exploited to yield substantial speedup in computation. Compared to the brute-force approach in [1], our algorithms yield about 44% improvement. Our technique is independent of the underlying computational or processor model, and thus can be implemented on top of any optimized solution. We demonstrate an improvement by about 19% and 13.5% in the worst case on top of the optimized solutions presented in [2] and [3].