Elliptical codebook for lattice vector quantization

A novel codebook design for lattice vector quantization that is better suited to the encoding of dyadic wavelet coefficients is proposed. This method deals with wavelet coefficients in horizontal or vertical orientation. The elliptical codebook allows better encoding of significant vectors corresponding to highest wavelet coefficients (strong edges). This improves visual quality. The present conclusions are supported by a comparative study of spherical and elliptical codebooks. The elliptical scheme associated with an optimal orientation allows one first to consider the neighboring wavelet-coefficient correlation, and then to credit the high ones representing edges. Those two points are partly responsible for the higher visual quality of the quantized image.<>