Display. Special Contribution from Asia Display/IDW'01. Enhancement of JPEG Coded Images Using a Region-based Algorithm.

We describe an improved post-processing algorithm that reduces the blocking and ringing artifacts caused by quantization noise of the DCT coefficients in block-coding techniques such as JPEG without excessively blurring. It is a region-based algorithm that is iteratively applied based on projection onto convex sets. It first segments the decoded image into three regions : the region where blocking artifacts are strongly presented, the region consisting of edge pixels, and the region where ringing artifacts are presented. A process for reducing quantization noise suitable for each region is then calculated. Finally, the DCT coefficients are modified in accordance with the quantization constraint. Some experimental results demonstrate that this algorithm effectively removes the blocking and ringing artifacts in each region without excessively blurring.