Removal of blocking and ringing artifacts in transform coded images

Block-based discrete cosine transform (BDCT) image coding techniques are widely used in image and video compression applications such as JPEG and MPEG. At a moderate bit rate, the BDCT is usually a quite satisfactory solution to most of practical coding applications. However, for high compression rates it produces noticeable blocking and ringing artifacts in the decompressed image. We propose a novel post-processing algorithm to remove the blocking and ringing effects at low bit rates. The main steps in this algorithm include block classification, boundary low-pass filtering and mid-point interpolation, edge detection and filtering, and DCT coefficient constraint. The improvement is demonstrated both subjectively and objectively.