DCT-based color image compression algorithm using adaptive block scanning

A lossy compression algorithm for still color images is presented. Based on DCT and using adaptive block scanning, the proposed method utilizes a simple technique to encode efficiently the DCT coefficients. The required image quality is guaranteed by using the bisection method to threshold the DCT coefficients of the YCbCr image gotten from the input RGB image. Four scan orders (zigzag, horizontal, vertical and hilbert) are used as adaptive block scanning to read the DCT coefficients from the retained DCT block coefficients. Following a scan order, an index vector is formed by the length of the zero-run sequence that preceded a nonzero DCT coefficient. The lowest value of the four index vectors maximums determines the best scan. Finally, the nonzero DCT coefficients and the index vector for each block are encoded to form the compressed image. The obtained results faced to those reported in recent methods show clearly that the proposed technique achieves high performances.