Deblocking of block-transform compressed images using weighted sums of symmetrically aligned pixels

Abstract

A new class of related algorithms for deblocking block-transform compressed images and video sequences is proposed in this paper. The algorithms apply weighted sums on pixel quartets, which are symmetrically aligned with respect to block boundaries. The basic weights, which are aimed at very low bit-rate images, are obtained from a two-dimensional function which obeys predefined constraints. Using these weights on images compressed at higher bit rates produces a deblocked image which contains blurred "false" edges near real edges. We refer to this phenomenon as the ghosting effect. In order to prevent its occurrences, the weights of pixels, which belong to nonmonotone areas, are modified by dividing each pixel's weight by a predefined factor called a grade. This scheme is referred to as weight adaptation by grading (WABG). Better deblocking of monotone areas is achieved by applying three iterations of the WABG scheme on such areas followed by a fourth iteration which is applied on the rest of the image. We refer to this scheme as deblocking frames of variable size (DFOVS). DFOVS automatically adapts itself to the activity of each block. This new class of algorithms produces very good subjective results and PSNR results which are competitive relative to available state-of-the-art methods.

Image Deblocking in Wavelet Domain Based on Local Laplace Prior

“…In Table 1, the PSNR results of the proposed method is compared with the best PSNR results obtained by any of the methods [5,13,23,24,25,26] as reported in [13]. The results show that for Lena, Barbara and Peppers images the proposed method outperforms the best results reported in [13].…”

“…Table 1. PSNR comparison between the proposed method and best results reported in [13] for restoration from JPEG compression with different Quality factors.…”

“…The techniques discussed in [11,12] use an overcomplete wavelet representation to reduce the blocking artifacts. Averbuch et al [13] proposed to apply weighted sums on pixel quartets which are symmetrically aligned to the block boundaries to suppress the blocking artifacts. The image deblocking scheme based on pointwise shape adaptive DCT (SA-DCT) [14] have shown excellent state of the art results which is able to remove both the blocking and ringing artifacts.…”

A Learning-Based Approach to Reduce JPEG Artifacts in Image Matting

“…[28,1,2,6]) aimed at reducing JPEG artifacts. These approaches target low-quality compressed images and perform various types of filtering to reduce blocking and ringing artifacts.…”

“…Even "high quality" JPEG images (e.g quality 9 2 ), which represent common compression level used on camera phones and social media sites, have subtle artifacts that can adversely affect the resulting alpha mattes.…”