Lapped RVQ and alphabet and entropy constraints

The paper reports on some methods to improve the performance of residual vector quantization (RVQ) for low bit rate image coding. The problem addressed is the direct application of RVQ-based techniques to coding images at low bit rates. In the first part of the paper, RVQs are investigated where vectors are allowed to overlap. The RVQ structure allows this to be done in stages and without increasing the bit rate, resulting in a reduction in blocking effects. In the second part of the paper, entropy-constrained RVQ is considered where an additional constraint is placed on the RVQ codebook to improve the reproduction quality given fixed memory constraints