Embedded Wavelet Packet Image Coder with Fast Rate-Distortion Optimized Decomposition

A fast rate-distortion (R-D) optimized wavelet packet (WP) transform is proposed for image compression in this research. By analyzing the R-D performance of the quantizer and the entropy coder, we show that the coding distortion D can be modeled as an exponentially decaying function as the coding rate R increases. With this exponential R-D model, it is proved that the constant R-D slope criterion for optimum bit allocation is equivalent to the constant distortion criterion, which can be easily implemented via thresholding. Based on this analytical result, we develop a fast wavelet packet decomposition scheme which is optimized in the R-D sense by comparing simple parameters associated with each wavelet packet band such as the 1st or 2nd absolute moments. We have performed extensive experiments to demonstrate the performance of an image coder using the proposed R-D optimized wavelet packet transform, and shown that our scheme is highly competitive with all well known state-of-the-art image coders.