Spherical representation in wavelet packets for image coding

In this paper, we present an adaptation of the spherical coder, which has been developed for wavelet transform, to wavelet packets. This coder uses local energy as a direct measure to differentiate the spatial information available in wavelet subbands and to decide how to allocate the available bitrate within each subband. As local energy becomes available at finer resolutions, i.e. in smaller size windows, the coder automatically updates its decisions about how to spend the bitrate. We use a hierarchical set of variables to specify and code the local energy up to the highest resolution, i.e. the energy of individual wavelet coefficients. The performance of the algorithm is improved by the use of optimal wavelet packet in terms of the energy distribution. The resulting coder achieves over 1 dB coding gain, especially for textured images.