A space and frequency hybrid algorithm to remove block artifacts

Postfiltering of block artifacts in decoded images has drawn extensive attention. But less improvements have been made for staircase noise. In this paper a space and frequency hybrid algorithm is presented. First, the edge information in the decoded images is extracted. Based on an analysis of artifacts in the frequency domain, the block effect in the edge image is removed by using a notch filter. The filtered edge image is used for a neighborhood analysis. A space-variant filter, consisting of a 2D LPF and a 1D directional LPF, is then applied to the decoded image to reduce artifacts. Which of the filters is chosen depends on the neighborhood analysis. Finally, the contrast is enhanced. The simulation results demonstrate that the proposed algorithm improves both the subjective visual quality and PSNR of decoded images effectively.