This paper introduces a new model-based soft decoding technique to restore the widely used joint photographic expert group(JPEG) streams.The image is modeled as a two dimensional(2D) piecewise stationary autoregressive process,and the decoding task is formulated as a constrained optimization problem.All the constraints are given by the quantization intervals which available at the decoder freely.The autoregressive model serves as an important regularization term of the objective function of the optimization,and the model parameters are solved on the decoded image locally using a weighted total least square method.In addition,a novel bilateral dualside weighting scheme is proposed to minimize the influence of the blocking artifact on the accuracy of parameter estimation.Extensive experimental results suggest that the proposed algorithm systematically improves the quality of JPEG images and also outperforms existing JPEG postprocessing algorithms in a wide bit-rate range both in terms of peak signal-to-noise ratio(PSNR) and subjective
