Compression of color images without visible blocking artifacts using a modified DCT computation scheme

The discrete cosine transform (DCT) is widely used in image compression and has been adopted in the lossy compression method of JPEG. At very low bit rates, however, severe blocking as well as color artifacts can be noticed with this algorithm. Another problem of the DCT is its computation time. The subband-DCT (SB-DCT), introduced by Jung et al. (1996), has been shown to have a better performance when used on grey scale images. In this paper we investigate the compression of color images using the SB-DCT. Different configurations regarding input data, subband-DCT and distribution of bits between the different components (YUV) have been tried to find the qualitatively best technique. We give experimental results on the higher computational speed of this approach. Quantitative and subjective testing methods are employed to show the higher quality of reconstructed images encoded using the SB-DCT as compared with those obtained using the standard DCT