1. A method for processing an image to provide deblocking filtering, the image being divided into a plurality of blocks, each block including a plurality of pixel lines perpendicular to a boundary with an adjacent block, the method comprising: dividing one or more of the plurality of blocks into a plurality of portions fewer than the plurality of pixel lines, each of the plurality of portions consisting of one or more pixel lines; calculating a decision value for each of the plurality of portions of a block based on values of pixels in a subset of pixel lines of the block; and judging whether or not to apply a deblocking filter to each of the plurality of portions of the block based on the respective decision value calculated for the portion, wherein the judging whether or not to apply a deblocking filter to each portion includes comparing the respective decision value calculated for the portion with a threshold value.