Encoder, decoder, encoding method, and decoding method

An encoding method comprising:

• changing values of luma pixels in a first block and a second block to filter a first boundary between the first block and the second block, using clipping such that change amounts of the respective values are within respective luma clip widths, the luma pixels in the first block and the second block being arranged along a first line across the first boundary;
• and
• changing values of chroma pixels in a third block and a fourth block to filter a second boundary between the third block and the fourth block, using clipping such that change amounts of the respective values are within respective chroma clip widths, the chroma pixels in the third block and the fourth block being arranged along a second line across the second boundary,
• wherein the luma clip widths applied to the luma pixels arranged along the first line are selected to be asymmetrical with respect to the first boundary, and
• wherein the chroma clip widths applied to the chroma pixels arranged along the second line are selected to be symmetrical with respect to the second boundary.