Apparatus and method of attenuating distortion introduced by a predictive coding image compressor.

摘要

The predictive coding method and related apparatus (100) which (a) computes a value D representing the difference between an original graylevel value for a current pixel and a predicted value for the current pixel; (b) associates (102) each successive range of D values to a respective quantization level, each quantization level QN having a respective QN value represen NOTELEMENT ing the range corresponding thereto; (c) sets (106) a respective QERR value to D for the current pixel, when the QN value is zero; (d) re-maps (108) m QERR values to n (n </= m) MERR values; assigns to the value MERR=0 those QERR values in which ¦QERR¦ </= (+Q1 VALUE)/2; (e) sums (110) the MERR values for successive pixels in a QN=Q0 region; and (f) adjusts (104) the QN value from the value of Q0 by the value of Q1 for a pixel at which the summed value reaches (112, 114) a predefined threshold. QN values, adjusted as appropriate, are subjected to entropy coding compression (120) and decompression. In the decompression process (126, 130), pixel values are reconstructed. According to the invention, the reconstructed values are subjected to a vertical filter (132) in which a pixel having a reconstructed value I0 is filtered to have a value I'0 = I0 + [(I-1 - I0)C- + (I+1 - I0)C+] wherein C+ and C- are respective predefined clamping values, and wherein I-1 and I+1 are the respective reconstructed values of pixels adjacently below and adjacently above the current pixel.