Encoder, decoder, encoding method, and decoding method

1. An encoder comprising:

processing circuitry; and

a memory coupled to the processing circuitry,

wherein, using the memory, the processing circuitry is configured to:

change values of pixels in a first block and a second block to filter a boundary between the first block and the second block, using clipping such that change amounts of the respective values do not exceed respective thresholds, the pixels in the first block and the second block being arranged along a line across the boundary;

wherein the respective thresholds for the pixels in the first block and the second block are selected to be symmetrical or asymmetrical with respect to the boundary based on block sizes of the first block and the second block;

wherein the pixels in the first block include a first pixel located at a first position, and the pixels in the second block include a second pixel located at a second position corresponding to the first position with respect to the boundary;

wherein the thresholds include a first threshold and a second threshold corresponding to the first pixel and the second pixel, respectively; and

wherein the first threshold is larger than the second threshold when the first block is larger than the second block.

2. The encoder according to claim 1 ,

wherein the pixels in the first block include a first additional pixel located at a first additional position and the pixels in the second block include a second additional pixel located at a second additional position which corresponds to the first additional position with respect to the boundary; and

the thresholds include a first additional threshold and a second additional threshold corresponding to the first additional pixel and the second additional pixel, respectively; and

wherein the first additional threshold is same as the second additional threshold.

3. The encoder according to claim 2 ,

wherein the boundary is constituted with the first additional pixel and the second additional pixel.

4. The encoder according to claim 1 ,

wherein at least one of the respective thresholds for the pixels located at respective positions in the first block is different from a threshold for the pixel located at a corresponding position in the second block with respect to the boundary.

5. A decoder comprising:

processing circuitry; and

a memory coupled to the processing circuitry,

wherein, using the memory, the processing circuitry is configured to:

change values of pixels in a first block and a second block to filter a boundary between the first block and the second block, using clipping such that change amounts of the respective values do not exceed respective thresholds, the pixels in the first block and the second block being arranged along a line across the boundary;

wherein the respective thresholds for the pixels in the first block and the second block are selected to be symmetrical or asymmetrical with respect to the boundary based on block sizes of the first block and the second block;

wherein the pixels in the first block include a first pixel located at a first position, and the pixels in the second block include a second pixel located at a second position corresponding to the first position with respect to the boundary;

wherein the thresholds include a first threshold and a second threshold corresponding to the first pixel and the second pixel, respectively;

wherein the first threshold is larger than the second threshold when the first block is larger than the second block.

6. The decoder according to claim 5 ,

wherein at least one of the respective thresholds for the pixels located at respective positions in the first block is different from a threshold for the pixel located at a corresponding position in the second block with respect to the boundary.

7. The decoder according to claim 5 ,

wherein the pixels in the first block include a first additional pixel located at a first additional position and the pixels in the second block include a second additional pixel located at a second additional position which corresponds to the first additional position with respect to the boundary; and

the thresholds include a first additional threshold and a second additional threshold corresponding to the first additional pixel and the second additional pixel, respectively; and

wherein the first additional threshold is same as the second additional threshold.

8. The decoder according to claim 7 ,

wherein the boundary is constituted with the first additional pixel and the second additional pixel.

9. An encoding method comprising:

changing values of pixels in a first block and a second block to filter a boundary between the first block and the second block, the pixels in the first block and the second block being arranged along a line across the boundary; and

performing clipping such that change amounts of the respective values do not exceed respective thresholds;

wherein the respective thresholds for the pixels in the first block and the second block are selected to be symmetrical or asymmetrical with respect to the boundary based on block sizes of the first block and the second block;

wherein the pixels in the first block include a first pixel located at a first position, and the pixels in the second block include a second pixel located at a second position corresponding to the first position with respect to the boundary;

wherein the thresholds include a first threshold and a second threshold corresponding to the first pixel and the second pixel, respectively; and

wherein the first threshold is wherein the first threshold is larger than the second threshold when the first block is larger than the second block.

10. The encoding method according to claim 9 ,

wherein the pixels in the first block include a first additional pixel located at a first additional position and the pixels in the second block include a second additional pixel located at a second additional position which corresponds to the first additional position with respect to the boundary; and

the thresholds include a first additional threshold and a second additional threshold corresponding to the first additional pixel and the second additional pixel, respectively; and

wherein the first additional threshold is same as the second additional threshold.

11. The encoding method according to claim 10 ,

wherein the boundary is constituted with the first additional pixel and the second additional pixel.

12. The encoding method according to claim 9 ,

wherein at least one of the respective thresholds for the pixels located at respective positions in the first block is different from a threshold for the pixel located at a corresponding position in the second block with respect to the boundary.

13. A decoding method comprising:

changing values of pixels in a first block and a second block to filter a boundary between the first block and the second block, the pixels in the first block and the second block being arranged along a line across the boundary; and

performing clipping such that change amounts of the respective values do not exceed respective thresholds;

wherein the respective thresholds for the pixels in the first block and the second block are selected to be symmetrical or asymmetrical with respect to the boundary based on block sizes of the first block and the second block;

wherein the pixels in the first block include a first pixel located at a first position, and the pixels in the second block include a second pixel located at a second position corresponding to the first position with respect to the boundary;

wherein the thresholds include a first threshold and a second threshold corresponding to the first pixel and the second pixel, respectively; and

wherein the first threshold is wherein the first threshold is larger than the second threshold when the first block is larger than the second block.

14. The decoding method according to claim 13 ,

wherein at least one of the respective thresholds for the pixels located at respective positions in the first block is different from a threshold for the pixel located at a corresponding position in the second block with respect to the boundary.

15. The decoding method according to claim 13 ,

wherein the pixels in the first block include a first additional pixel located at a first additional position and the pixels in the second block include a second additional pixel located at a second additional position which corresponds to the first additional position with respect to the boundary; and

the thresholds include a first additional threshold and a second additional threshold corresponding to the first additional pixel and the second additional pixel, respectively; and

wherein the first additional threshold is same as the second additional threshold.

16. The decoding method according to claim 15 ,

wherein the boundary is constituted with the first additional pixel and the second additional pixel.