Wavelet packet coding with jointly optimized lattice vector quantization and data rate allocation

Describes a new coding scheme based on a joint optimization of signal decomposition and of lattice vector quantizers. The adaptive signal decomposition uses wavelet packets that allow to best match the decomposition to the signal nonstationary characteristics. In order to obtain a good tradeoff between frequency and spatial localization, nonstationary wavelet packets based on filters varying at each stage of the tree structured decomposition are considered. The complete tree is pruned into the best basis subtree which minimizes a perceptually weighted distortion for a given bit rate. Each subband is then quantized using data rate constrained lattice vector quantizers. The choice of the quantizer is usually determined by the minimization of the overall mean squared error of the reconstructed signal under the constraint of a given bit rate [Ramchandran and Vetterli, 1993]. However, this procedure is not optimum in terms of visual quality. A procedure of quantization based on the minimization of perceptually weighted distortion of each frequency band is introduced. The results show a very significant improvement both in terms of SNR and of visual quality versus the JPEG algorithm.<
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