Adaptive postprocessor for block encoded images

Blocking effects are a major degradation in block based image coding techniques. In this paper, we propose an adaptive postprocessor for the removal of blocking effects. The adaptation is achieved by changing filter coefficients according to the local characteristics of images and the blocking effects. Here, a space-variant lowpass filter is used to smooth the pixels at block boundaries where the blocking effects are highly visible. In addition, the pixels that are closed to an edge are adaptively regional or directional lowpass filtered if the blocking effects are obvious. As for the pixels at edges, they are left untouched by the postprocessor. Therefore, blocking effects can be removed without blurring the edge sharpness. Performance improvements compared with other techniques are obtained according to simulation results. The proposed postprocessor has 0-1 dB gain (depending on the images) compared with the loop filter of H.261, the linear filter, and the nonlinear space-variant postprocessor