Adaptive processing with quadratic programming and LPF for reducing blocking artifacts in DCT image coding

In many image coding methods, the discrete cosine transform (DCT) is used. When the compression ratio is increased, blocking artifacts are generated i n the reconstructed image due to quantization error. To resolve this proble m, a method is proposed to adaptively change the suppression process of dis tortion depending on the block. In this method, each block is classified in to (1) the flat part where the pel values change monotonically by the value of the received DCT coefficient and (2) the dynamic part. In the block in the flat part, the DCT coefficients are estimated within the quantization w idth by the quadratic programming method, and the block is regenerated by r eplacing the received coefficients. The continuity at the block boundary an d the boundary pel values after smoothing are used as the objective functio n. Higher-order DCT coefficients can be estimated successively. In the regi on where the variation of the pel values is substantial, human visual sensi tivity is not sufficient for the distortion. Therefore, the block boundary is smoothed with a low-pass filter (LPF) in the block in the variable part. This method is used for processing of several images. It is demonstrated t hat the SNR is better than those in the JPEG reconstruction method, ac coef ficient prediction:method, and the LPF method. Overall, a high-quality reco nstructed image is obtained with the blocking artifacts are suppressed. (C) 2000 Scripta Technica.