Variable-rate finite-state vector quantization and applications to speech and image coding

Two variable rate versions of the finite-state vector quantizer introduced by J. Foster, M.O. Dunham, and R.M. Gray (FDG) (1985) are presented, with the possibility of using structured as well as unstructured state codebooks. In the first scheme, the state codebook sizes can be different for different states, implying different rate distribution among the states. In the second scheme, in addition to this flexibility, pruned tree-structured vector quantizers are used as the state quantizers, i.e., each of the state quantizers can be a variable-rate encoder. For encoding sampled speech data, both schemes perform significantly better than the fixed-rate FDG scheme, and the second scheme gives the best performance of all. The 2-D extension of the above schemes is considered, and two low-bit rate image coding systems based on them are described