A method of de-blocking an edge (709, 711) of a block of samples in a frame of sample data, the method comprising: decoding a first prediction mode for a first block of two adjacent blocks (803, 805) of sample data, each of the blocks (803, 805) of sample data including a primary colour channel and at least one secondary colour channel; decoding a second prediction mode for a second block of the two adjacent blocks (803, 805) of sample data; determining a boundary strength value for a block of samples (704, 706) along an edge (709, 711) corresponding to a boundary between said first block of sample data and said second block of sample data if the first prediction mode and the second prediction mode are both intra-block copy, wherein the boundary strength value indicates application of a weak de-blocking filter (330, 430) if block vectors (524, 608, 612) associated with the two adjacent blocks (803, 805) are different, and indicates no de-blocking filtering is applied if the block vectors (524, 608, 612) are equal; and applying the weak de-blocking filter (330, 430) to the block of samples (704, 706) along said edge (709, 711) of the two blocks (803, 805) if the determined boundary strength value indicates that the weak de-blocking filter (330, 430) should be applied, the weak de-blocking filter (330, 430) having a filter strength that is less than the filter strength of a de-blocking filter that is applied to an edge determined to have two, adjacently located, intra prediction mode blocks (813, 815), the method being characterized in that the block vectors (524, 608, 612) have an integer pixel precision and reference a block of samples (526, 610, 614) in the frame, and also in that the weak de-blocking filter (330, 430) is applied to the primary colour channel of the block of samples (704, 706) along said edge (709, 711) without also applying a de-blocking filter to the at least one secondary colour channel of the block of samples (704, 706) along said edge (709, 711). decoding a first prediction mode for a first block of two adjacent blocks (803, 805) of sample data, each of the blocks (803, 805) of sample data including a primary colour channel and at least one secondary colour channel; decoding a second prediction mode for a second block of the two adjacent blocks (803, 805) of sample data; determining a boundary strength value for a block of samples (704, 706) along an edge (709, 711) corresponding to a boundary between said first block of sample data and said second block of sample data if the first prediction mode and the second prediction mode are both intra-block copy, wherein the boundary strength value indicates application of a weak de-blocking filter (330, 430) if block vectors (524, 608, 612) associated with the two adjacent blocks (803, 805) are different, and indicates no de-blocking filtering is applied if the block vectors (524, 608, 612) are equal; and applying the weak de-blocking filter (330, 430) to the block of samples (704, 706) along said edge (709, 711) of the two blocks (803, 805) if the determined boundary strength value indicates that the weak de-blocking filter (330, 430) should be applied, the weak de-blocking filter (330, 430) having a filter strength that is less than the filter strength of a de-blocking filter that is applied to an edge determined to have two, adjacently located, intra prediction mode blocks (813, 815),