Encoder, decoder, and related non-transitory computer readable medium

An encoder comprising:

• processing circuitry;
• and
• a memory coupled to the processing circuitry,
• wherein the processing circuitry is configured to:
• determine whether to filter a boundary between a first block and a second block adjacent to the first block;
• select a filter based on a block size of the first block and a block size of the second block in an image, the filter including a first set of multipliers and a first set of offsets for the first block, and a second set of multipliers and a second set of offsets for the second block;
• and
• change values of pixels in the first block and the second block, by performing multiplication with each multiplier in the first set of multipliers, by performing multiplication with each multiplier in the second set of multipliers, and by using the first set of offsets and the second set of offsets, the pixels in the first block and the second block being arranged along a straight line across the boundary between the first block and the second block,
• wherein the first set of multipliers and the second set of multipliers are asymmetrical with respect to the boundary, and
• wherein the first set of offsets and the second set of offsets are symmetric with respect to the boundary.

A non-transitory computer readable medium storing a bitstream, the bitstream comprising filter information that causes a decoder to execute a filtering process, the filtering process comprising:

• determining whether to filter a boundary between a first block and a second block adjacent to the first block;
• selecting a filter based on a block size of the first block and a block size of the second block in an image, the filter including a first set of multipliers and a first set of offsets for the first block, and a second set of multipliers and a second set of offsets for the second block;
• and
• changing values of pixels in the first block and the second block, by performing multiplication with each multiplier in the first set of multipliers, by performing multiplication with each multiplier in the second set of multipliers, and by using the first set of offsets and the second set of offsets, the pixels in the first block and the second block being arranged along a straight line across the boundary between the first block and the second block,
• wherein the first set of multipliers and the second set of multipliers are asymmetrical with respect to the boundary, and
• wherein the first set of offsets and the second set of offsets are symmetric with respect to the boundary.