A 3-D block transform based approach to color image compression

In this paper, we present a novel approach to color image compression using 3-D block transforms. Unlike, most of the other color image compression schemes, the proposed scheme do not transform the highly correlated RGB color components into a decorrelated color space like YUV, YCrCb etc but uses 3-D block transforms which is applied directly on RGB color components to reduce the intercolor redundancy, then the 3-D block transform coefficients are quantized and entropy coded. Two different transforms are used in this work, the first is 3-D Discrete cosine transform (DCT) and the second is Mixed transform. The Mixed transform consists of the Lapped Bi-orthogonal Transform in vertical and horizontal directions and DCT in temporal direction. The 3-D DCT exhibits blocky artifacts at low bit rates but Mixed transform gives better visual results. Both transform produces NxNx3 transform coefficients when applied on a NxNx3 3-D data block. We propose a wavelet structure for 3-D block transform coefficients which enables a very efficient encoding of the 3-D block transform coefficients at exact desired bit rate. Our proposed coder shows encouraging results when compared to the Rate Distortion performance of JPEG baseline coder and JPEG2000 coder. The R-D performance of the proposed coder outperforms the JPEG baseline coder consistently by a large margin and is roughly comparable to the JPEG2000 coder.