MINIMAL ERROR DRIFT IN FREQUENCY SCALABILITY FOR MOTION-COMPENSATED DCT CODING

We mathematically analyze the drift of low-resolution images obtained from a smaller IDCT of a subset of the DCT coefficients of the full-resolution images in motion-compensated hybrid predictive/DCT coding such as MPEG-2, which allows for frequency scalability. Using this mathematical structure, we derive a low-resolution decoder that has the theoretically minimum possible drift, and propose techniques for implementation that produce substantial improvement in real sequences. The minimum drift can also be used as a milestone, to be compared with other techniques of drift reduction (of worse performance but lower complexity). For the case where leakage is used to reduce the drift, we determine a minimum-energy non-uniform DCT-domain leakage matrix which is no more complex than uniform leakage, but gives a substantial improvement. Finally, we note that DCT-based pyramidal coding is essentially the same as the drift case, and thus we use the same mathematical structure to derive the theoretically-best upward predictor in pyramidal coding.