Image coding with variable rate RVQ

A new residual vector quantizer (RVQ) design algorithm is modified so that the multistage structure can be exploited to produce variable-rate RVQ (VR-RVQ) systems. VR-RVQ systems are shown to have very useful properties: (1) the codebook storage requirement and the search complexity are both reduced; (2) the VR-RVQ system is able to exploit the spatial variance of perceptually important information; and (3) the VR-RVQ codebook can operate over a wide range of rates, without having to store several codebooks. Experiments were performed using VR-RVQ systems with vectors of many sizes, and results show significant improvement over fixed-rate RVQ systems with the same block size