In order to remove blocking artefacts from a frame which has been coded by blocks and then decoded, a certain number of pixels (n) is selected for examination from both sides of the block boundary (30). The number of pixels selected for examination depends on the image content of the frame in the environment of the block boundary, particularly on the difference of the pixel values across the block boundary (30) and the size of the quantization step of the transformation coefficients used in the transformation coding of the blocks.