Improving the image quality of block-based video coders by exploiting interblock redundancy

Narrowband video transmission via ISDN or wireless channels requires high compression factors. Common block-based coders achieve this by taking account of the statistical correlations within the image blocks. Correlations between neighbouring image blocks, however, are neglected. We present an approach using discrete cosine transforms which takes advantage of this additional information hidden in the statistical dependencies between neighbouring blocks in order to improve the image quality of the decoder. The luminance of the current block to be coded is predicted from the surrounding image blocks in order to correct coding errors. By this means the annoying blocking artefacts will be reduced. A smooth and well-balanced image display results. At the same time edges of real objects are undisturbed, thus the sharpness remains.