ADAPTIVE POSTPROCESSOR FOR BLOCK ENCODED IMAGES

Blocking effects are a major degradation in block based image coding t echniques, In this paper, we propose an adaptive postprocessor for the removal of blocking effects. The adaptation is achieved by changing f ilter coefficients according to the local characteristics of images an d the blocking effects. Here, a space-variant lowpass filter is used t o smooth the pixels at block boundaries where the blocking effects are highly visible, In addition, the pixels that are closed to an edge ar e adaptively regional or directional lowpass filtered if the blocking effects are obvious, As for the pixels at edges, they are left untouch ed by the postprocessor. Therefore, blocking effects can be removed wi thout blurring the edge sharpness. Performance improvements compared w ith other techniques are obtained according to simulation results. The proposed postprocessor has el dB gain (depending on the images) compa red with the loop filter of H.261 [1], the linear filter [2], and the nonlinear space-variant postprocessor [3].