A deblocking filtering control comprises checking whether pixel values of four pixels (12, 22) in a line (15) of pixels (12, 22) in a block (10) of pixels (12) and in a neighboring block (20) of pixels (22) form an approximate line. If the pixel values of the four pixels (12, 22) in the line (15) of pixels (12, 20) in both the block (10) of pixels (12) and in the neighboring block (20) of pixels (22) form an approximate line the deblocking filtering control selects to apply strong deblocking filtering to pixel values in the line (15) of pixels (12, 22). The subject and objective quality of the deblocking filtering is thereby improved by applying strong deblocking filter to areas where the signal in a picture (1) not only has the form of a flat line but also form a ramp.