An effective and flexible image enhancement algorithm in compressed domain

Images with JPEG format using discrete cosine transform (DCT) is selected for most popular compression standards. Enhancement in the compressed domain offers two major advantages, including low computational complexity and storage space. However, the compression is achieved by block-based transform; therefore, it is hard to enhance image globally. In this paper, the main issue is to develop a global enhancement method that effectively reduces the introduced blocking artifacts and achieves excellent visual quality of enhancement. We propose a combined DCT matrix representation, which consists of 8n x 8n pixel arrays, to enhance the global information on images for removing block artifacts in compressed-domain. In addition, we propose the multi-enhancement factors based on spatial frequency for image enhancement in compressed domain. From the simulation results, the proposed method achieves not only excellent improvement for image enhancement but also reducing the blocking artifacts significantly.