Patent ID: 7242815

Claim:
A video encoder comprising a block boundary filtering block for removing blocking artefacts due to block boundaries between image blocks in a frame of a digital video signal, the block boundary filtering block being arranged to perform an adaptive block boundary filtering operation on a block boundary between a first image block on a first side of the block boundary and a second image block on a second side of the block boundary by: selecting a certain number of pixels for examination on both sides of the block boundary; determining a first activity measure representative of a variation in pixel value between pixels on the first side of the block boundary by examining the values of pixels selected for examination on the first side of the block boundary; determining a second activity measure representative of a variation in pixel value between pixels on the second side of the block boundary by examining the values of pixels selected for examination on the second side of the block boundary; selecting a number of pixels to be filtered from the pixels selected for examination; determining a new value for a pixel selected for filtering on the first side of the block boundary on the basis of pixels that appear in a filtering window set around the pixel to be filtered, the size of the filtering window being dependent at least in part upon the first activity measure determined on the first side of the block boundary; and determining a new value for a pixel selected for filtering on the second side of the block boundary on the basis of pixels that appear in a filtering window set around the pixel to be filtered, the size of the filtering window being dependent at least in part upon the second activity measure determined on the second side of the block boundary.