FAST ALGORITHMS FOR DCT-DOMAIN IMAGE DOWN-SAMPLING AND FOR INVERSE MOTION COMPENSATION

Straightforward techniques for spatial domain processing of compressed video via decompression and recompression are computationally expensi ve. We describe an alternative approach wherein the compressed stream is processed in the compressed, discrete cosine transform (DCT) domain without explicit decompression and spatial domain processing, so that the output compressed stream, corresponding to the output image, conf orms to the standard syntax of 8 x 8 blocks, We propose computation sc hemes for down-sampling and for inverse motion compensation that are a pplicable to any DCT-based compression method, Worst-case estimates of computation savings vary between 37% and 50% depending on the task. F or typically sparse DCT blocks, the reduction in computations is more dramatic, A by-product of the proposed approach is improvement in arit hmetic precision.