title: CONCOLOR: Constrained Non-Convex Low-Rank  Model for Image Deblocking.
abstract: Due to independent and coarse quantization of transform coefficients in each block, block-based transform coding usually introduces visually annoying blocking artifacts at low bitrates, which greatly prevents further bit reduction. To alleviate the conflict between bit reduction and quality preservation, deblocking as a post-processing strategy is an attractive and promising solution without changing existing codec. In this paper, in order to reduce blocking artifacts and obtain high-quality image, image deblocking is formulated as an optimization problem within maximum a posteriori framework, and a novel algorithm for image deblocking using constrained non-convex low-rank model is proposed. The ℓ(p) (0 < p < 1) penalty function is extended on singular values of a matrix to characterize low-rank prior model rather than the nuclear norm, while the quantization constraint is explicitly transformed into the feasible solution space to constrain the non-convex low-rank optimization. Moreover, a new quantization noise model is developed, and an alternatively minimizing strategy with adaptive parameter adjustment is developed to solve the proposed optimization problem. This parameter-free advantage enables the whole algorithm more attractive and practical. Experiments demonstrate that the proposed image deblocking algorithm outperforms the current state-of-the-art methods in both the objective quality and the perceptual quality.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.forename: Ruiqin
authors.initials: R
authors.lastname: Xiong
authors.forename: Chen
authors.initials: C
authors.lastname: Zhao
authors.forename: Yongbing
authors.initials: Y
authors.lastname: Zhang
authors.forename: Siwei
authors.initials: S
authors.lastname: Ma
authors.forename: Wen
authors.initials: W
authors.lastname: Gao