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 sub-bands, 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.