ADAPTIVE HIERARCHICAL VECTOR QUANTIZATION FOR IMAGE-CODING - NEW RESULTS

Adaptive hierarchical algorithms of vector quantization (VQ) for image coding are proposed. First the basic codebook is generated adaptively using adaptive VQ, then the quadruplets of codes/indices in the so-ca lled zigzag order are coded into higher level (second and third levels ) codes by creating the second- and third-level index codebooks to red uce the redundancy presented in the codes. Partially matched quadruple ts are also encoded in the second and third layers using the index cod ebooks along with corresponding correction schemes. The third-layer en coding achieves a better compression ratio than a two-layer encoding s cheme, which was shown to be optimal when partial encoding was not ado pted. This three-layer coding scheme achieves better compression with no extra distortion and little extra computation. Experiments show enc ouraging results.