A first filter decision value is calculated for a block of pixels in a video frame based on pixel values of pixels in a first line (12) of pixels in the block. A second filter decision value is also calculated for the block based on pixel values of pixels in a corresponding first line of pixels in a neighboring block in the video frame. The first filter decision value is used to determine how many pixels in a line of pixels in the block to filter relative to a block boundary between the block and the neighboring block. The second filter decision value is used to determine how many pixels in a corresponding line of pixels in the neighboring block to filter relative to the block boundary.