METHOD AND APPARATUS FOR SPATIAL FILTERING OF DIGITAL IMAGE DECODED BY BLOCK CONVERSION

摘要

PURPOSE: To reduce or remove the disturbance effect of digital image before projecting the image on a screen after encoding/decoding by block conversion. CONSTITUTION: The block conversion causes the discontinuity of luminosity levels concerning pixels D and E in the border area of blocks BL1 and BL2. The discontinuity of these levels is detected from a change in the signs of two luminosity gradients respectively calculated between the levels of two pixels C and E adjacent to each pixel D in the given border area. A luminosity level NL of the pixel D in the border area is corrected by the jump ED of discontinuity equal with the absolute value of difference in the arithmetic average with the luminosity level of adjacent pixel by a discontinuity correction rate FCD evaluated corresponding to a quantization pitch allocated to the block BL1. Next, the block BL1 is corrected as a whole for reducing luminosity level difference caused by encoding/decoding between two adjacent blocks BL1 and BL2.