Minimum distortion quantizer for fixed-rate 64-subband video coding

A motion-compensated sub-band coding (SBC) scheme for video signals, featuring fixed-rate and optimum quantizer, is presented. Block matching algorithm provides a suitable inter-frame prediction, and a 64 sub-band decomposition allows a high decorrelation of the motion- compensated difference field. The main drawback is that sub-bands containing sparse data of different statistics are produced, thus requiring run-length (RL) and variable length coding (VLC) for best performance. However, most digital communication channels operate at constant bit-rate (BR); hence, fixed-rate video coding is the main goal, in order to reduce buffering delays. The approach followed in this work is modeling the subbands as independent memoryless sources with generalized Gaussian PDFs and designing optimum uniform quantizers with the goal of minimizing distortion after a BR value, also accounting for the entropy of the RLs of zero/nonzero coefficients, has been specified. The problem is stated in terms of entropy allocation among sub-bands minimizing the overall distortion, analogously to optimal distortion allocation when fixed quality is requested. The constrained minimum is found by means of Lagrange multipliers, once the parametric PDFs have been assessed from true TV sequences. This procedure provides the optimum step for uniform quantization of each sub-band, thus leading to discarding some of the least significant ones.