Artifact reduction by post-processing in image compression

In this chapter, the post-processing techniques developed for reducing artifacts in low bit rate image compression will be discussed. They mainly emphasize the reduction of blocking and ringing artifacts, on which brief discussions will be given first. Then a review of recent developments on deblocking filters will be presented. Specifically, an adaptive DCT domain postfilter will be described in detail. Though the approach was designed to remove blocking artifacts, interestingly it is also observed to be capable of suppressing ringing artifacts in block-based DCT image compression. Following that, recent works on the ringing artifact reduction will be reviewed. The de-ringing techniques tailored for the DCT and wavelet transform based compression will both be discussed.