Study Of De-Blocking And Enhancement Technology On Compressed Image In DCT Domain

With the development of the technology in the network communication and multimedia, the compressing of image and video becomes more important. Nowadays, a lot of image/video encoding standard compress and transform images in the form of"block DCT+ quantify", but high compress rate or improper quantify would introduces many distortions, especially the blocking artifacts can do a most bad influence to the subjective quality in a low bitrate decoding. Because those coding standards are fixed, the post-processing becomes most important to eliminate coding effects. Restraining blocking artifacts in the DCT domain can enhance the operation efficiency. Compared to exsisted de-block algorithms, our proposed algorithm can protect the image details when deblocking. Our enhance algorithms can alleviate blocking artifacts while operating enhancement.This dissertation is contributed in post-processing in DCT domain including deblocking and image enhancement.In the field of deblocking, based on the analysis of the reason of blocking artifacts, we propose a new POCS based de-blocking method in DCT domain called"POCS based Four Overlapped Neighbor Macro-blocks Smooth and Average De-block Algorithm(PFOSA)". The experiments show that our proposed method is superior to the exsitied POCS algorithms and AVS loopfilter in PSNR and the subjective quality.In the field of enhancement, aim at the worse vision effect when enhance the contrast of the images on BDCT, we proposed two algorithms. They can not only get rid of blocking artifacts, noises, and ringing effect, but also can avoid blurring of the edge areas. The EME and MGBIM are also adopted to evaluate the blocking and the efficiency of enhancement.