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
High-speed high-resolution analog-to-digital(A/D) conversion demanded by ultra wideband(UWB) signal processing is a very challenging problem.This paper proposes a parallel random projection method for UWB signal acquisition.The proposed method can achieve high sampling rate,high resolution and technical feasibility of hardware implementation.In the proposed method,an analog UWB signal is projected over a set of random sign functions.Then the low-rate high-resolution analog-to-digital convertors(ADCs) are used to sample the projection coefficients.The signal can be reconstructed by simple linear calculation with the sampling matrix,without complying with optimization algorithm and prior knowledge.In other aspects,unlike other approaches that need to utilize an accurate time-shift at extremely high frequency,or design a hybrid filter bank,or generate specific basis functions or work for signals with prior knowledge,the proposed method is a universal sampling approach and easy to apply.The simulation results of signal to noise ratio(SNR) and spurious-free dynamic range(SFDR) validate the efficiency of the proposed method for UWB signal acquisition.
