A combined-transform coding (CTC) scheme for image data compression

The authors propose a combined-transform-coding (CTC) scheme to reduce the blocking effect due to division of subblocks and to achieve better subjective performance. The proposed CTC scheme is described, and its information-theoretic properties are investigated. A comparison between the CTC scheme and conventional discrete cosine transform (DCT) and discrete Walsh-Hadamard transform (DWHT) schemes was made to demonstrate the performance improvement of the proposed scheme. The advantages of the CTC scheme also include (1) no ringing effect due to the absence of error propagation across block boundaries, (2) no additional computation, and (3) the ability to hold distortion below a certain threshold. In addition, it was found that the idea of combined coding can also be used in noiseless coding.<
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