Region adaptive spectral transformation For wavelet based color image compression

Abstract

In general, each region of a color image exhibits different spectral characteristics. Therefore, the energy compaction characteristic of a single global spectral transformation is rather weak for compression purposes. In this paper, we propose that different groups of wavelet coefficients of a color image be subjected to different spectral transformations prior to the spectral planes being coded by a wavelet-based image coder such as CSPIHT (Color Set Partitioning in Hierarchical Trees, [7]). The decomposition of the color image into such groups is succintly represented with a quadtree structure which is optimized for rate-distortion performance by means of a known analytical rate-distortion model for wavelet-based image codecs. The experiments show that, when integrated with the CSPIHT coder, the proposed region adaptive transformation method yields compression gains of 0.4–0.5 dB, on the average, for rates between 0.5bpp and 2.5bpp over the single global transformation method.