Advances in recursive per-pixel estimation of end-to-end distortion for application in H.264

This paper is concerned with open questions and modifications to expand the applicability of the recursive optimal per-pixel estimate (ROPE) of end-to-end distortion, which are particularly relevant to H.264. One open question involves the emergence of cross-correlation terms in the case of sub-pixel prediction or other pixel filtering operations. A new and improved low-complexity approximation is proposed, which accounts for the inter-pixel distance. Another open question involves the commonly ignored effects of rounding and clipping. The cumulative impact of rounding on the distortion estimate is shown to be extensive at low to medium packet-loss rates. Two schemes are proposed for effective rounding and clipping error compensation. Simulation results for H.264 with 1/4-pel prediction show that the revised ROPE maintains low complexity and achieves estimation accuracy that closely matches that of ROPE in the simpler case of full-pixel prediction, where it is optimal.