Lossless compression of VQ indexes using search-order and correction codes

In a fixed-rate vector quantization system, an image is divided into smaller blocks, and each block is usually independently encoded by an index of the same length that points to the closest codevector in the codebook. Recently, an algorithm called search-order coding has been proposed to further reduce the bit rate by encoding the indexes but without introducing any extra encoding distortion. We present an improved algorithm that extends the idea of the search-order coding algorithm by encoding the indexes pair by pair. In addition, the correction codes are also adopted to improve the bit rate further. Simulation results indicate that our algorithm is able to achieve a bit rate up to 7% lower than the search-order coding algorithm.