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

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 by Chang and Messerschmitt (1995) and fast algorithm based on factorization of the DCT matrix is proposed by Merhav and Bhaskaran (see IEEE International Conference on Acoustics, Speech, and Signal Processing Conference Proceedings, vol.4, p.2307-10, 1996). These schemes, however, treat each 8/spl times/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 of Chang et al., our algorithms yield about a 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 by Merhav and Bhaskaran and by Assuncao and Ghanbari (see ICASSP 1997, p.2633-36, 1997).