Fast Edge-Preserved Postprocessing for Compressed Images

Images are often coded using block-based discrete cosine transform (DCT), where blocking and ringing artifacts are the most common visual distortion. In this letter, a fast algorithm is proposed to alleviate the said artifacts in the DCT domain. The new concept is to decompose a row or column image vector to a gradually changed signal and a fast variational signal, which correspond to low-frequency (LF) and high-frequency (HF) DCT subbands, respectively. Blocking artifacts between adjacent LF blocks are suppressed by smoothing LF components and discarding invalid HF ones, and ringing artifacts inside HF vectors are reduced by a simplified bilateral filter. With such a process, edges are preserved while blockiness and ringing are alleviated. Analytic and experimental results confirm the robustness and computational efficiency of the proposed method