Block position dithering in DCT-coded sequences

摘要

An attempt has been made to hide the false edges perceived at block borders in DCT-coded image sequences. The standard H.261 codec is extended by simple pre- and postprocessing: shifting the input image over small pseudo-random horizontal and vertical distances and shifting back the output image by the same amount. A subjective comparison by a panel of 20 observers has established a quality improvement for interframe coding, if both the current image and the previous image are subjected to the same shift. Masking the block borders by adding a time-invariant noise image to the output is found to be a desirable option.