Study Of Video Encode Post-processing Techniques Based On DCT

Along with the fast development of modern communication and computer techniques, the requirements for image information are increasing quickly. Because of huge image information, it must be compressed before being transmitted in real-time communication through the band-limited channel. The BDCT is a fundamental component of many international image and video compression standards. However, the compression method based on BDCT often cause blocking artifacts due to low bit rates. The two main causes that images are distorted are transmission error and quantization error. Several post-processing techniques are discussed to improve the quality of decoded image in this paper.Firstly, the reason causing blocking artifacts in BDCT compressed image is analyzed, and the difference between loop-filtering and post-filtering is compared; the post-processing techniques of H.263+ are presented. Then the de-blocking filter of H.263+ is studied and simulated.Secondly, several de-blocking algorithms based on image enhancement are realized and an improved method in DCT domain is proposed. The characteristic of human visual system (HVS) is sufficiently utilized in the algorithm. The model of blocking artifacts is built and an effective edge detection method is introduced. For smooth region, the parameter that affects blocking artifacts is modified and the step-function block is replaced with linear-function block. In the end, the DCT domain post-filtering method is applied to the updated block and texture region. The proposed method shows good performance in reducing blocking artifacts at different quantization steps for various kinds of images.Finally, a post-processing technique based on POCS is introduced and validated. By detecting the undesired high-frequency components, mainly caused by blocking artifacts, a new SCS and its operator is introduced; in addition, a improved QCS is presented using the correlation of DCT coefficients between adjacent blocks.In this paper, various types of post-processing techniques including the improved algorithm are discussed and compared through lots of experiments, and meaningful research and trial on post-processing technique of video coding has been carried out.