A COMBINED-TRANSFORM CODING (CTC) SCHEME FOR IMAGE DATA-COMPRESSION

Transform coding has been used successfully for image compression in many applications. However, it suffers from the artifact known as "blocking effect" due to division of subblocks. In this paper, we propose a combined-transform coding (CTC) scheme to reduce this effect and achieve better subjective performance. First the proposed CTC scheme was described and its information-theoretic properties were investigated. Then a comparison between the CTC scheme and conventional DCT and DWHT was made to demonstrate the performance improvement of the proposed scheme. The advantages of the proposed CTC scheme also include (1): no ringing effect due to no error propagation across block boundaries, (2): no additional computation and (3): the ability to hold distortion below a certain threshold. In addition, we found that the idea of combined-coding can also be used in noiseless coding and slight improvement in the compression performance can also be achieved if used properly.