A projection-based post-processing technique to reduce blocking artifact using a priori information on DCT coefficients of adjacent blocks

We propose a novel post-processing technique based on the theory of projections onto convex sets (POCS) to reduce the blocking artifacts in decoded images. Assuming that original image is highly correlated, the global frequency characteristics in two adjacent blocks may be similar to the local one in each block. Thus, we can consider the high frequency components of the global characteristics that do not exist in the local one as the effect caused by blocking artifact. We employ N-point DCT to obtain the local characteristics, and 2N-point DCT to obtain the global one, and then derive the relation between N-point and 2N-point DCT coefficients. The comparison of N-point with 2N-point DCT coefficients makes it possible to detect the undesired high frequency components, caused by the blocking artifact. From the above notion, we propose novel convex sets and their projection operators in the DCT domain. Results of performance evaluation show that regardless of image contents, the proposed technique is superior to the conventional ones, in terms of objective quality, subjective quality and convergence behavior.