On the robustness of vector set partitioning image coders to bit errors

A vector enhancement of Said and Pearlman´s Set Partitioning in Hierarchical Trees (SPIHT) methodology, named VSPIHT has recently been proposed for embedded wavelet image compression. A major advantage of vector based embedded coding with fixed length VQs over scalar embedded coding, is its superior robustness to noise. In this work we show that vector set partitioning can effectively alter the balance of bits in the bit stream so that significantly fewer critical bits carrying significant information is transmitted, thereby improving inherent noise resilience. Additionally, the degradation in reconstruction quality caused by errors in non-critical quantization information, can be reduced by appropriate VQ indexing, or designing channel optimized VQs for the successive refinement systems. For very noisy channels unequal error protection to the critical and non critical bits with either block codes or convolution codes are used. Extensive simulation results are presented