Method and apparatus for boundary handling in video coding

1. A method for filtering in video coding, comprising:

buffering, by a processor, first boundary pixel values of a subset of first reconstructed samples at a first node along a loop filter chain, a non linear mapping based filter and a constrained directional enhancement filter being applied to the first boundary pixel values, the non linear mapping based filter and the constrained directional enhancement filter being applied in the loop filter chain before a loop restoration filter, the first boundary pixel values being values of pixels at a frame boundary;

buffering, by the processor, second boundary pixel values of a subset of second reconstructed samples at a second node along the loop filter chain, the second reconstructed samples at the second node being generated after at least one of the non linear mapping based filter or the constrained directional enhancement filter is applied to the loop filter chain, and the second boundary pixel values being values of the pixels at the frame boundary; and

applying, by the processor, the loop restoration filter on to-be filtered reconstructed samples based on the buffered first boundary pixel values of the subset of the first reconstructed samples and the buffered second boundary pixel values of the subset of the second reconstructed samples.

2. The method of claim 1 , wherein the non linear mapping based filter is at least one of a cross-component sample offset (CC SO) filter and a local sample offset (LSO) filter.

3. The method of claim 1 , wherein the first reconstructed samples at the first node are input of the non linear mapping based filter.

4. The method of claim 3 , wherein

the second reconstructed samples at the second node are generated after an applying of sample offsets generated by the non linear mapping based filter.

5. The method of claim 4 , further comprising:

combining, by the processor, the sample offsets generated by the non linear mapping based filter with output of the constrained directional enhancement filter to generate the second reconstructed samples.

6. The method of claim 4 , further comprising:

combining, by the processor, the sample offsets generated by the non linear mapping based filter with the first reconstructed samples to generate intermediate reconstructed samples; and

applying, by the processor, the constrained directional enhancement filter to the intermediate reconstructed samples to generate the second reconstructed samples.

7. The method of claim 3 , further comprising:

combining, by the processor, the second reconstructed samples at the second node with sample offsets generated by the non linear mapping based filter to generate the to-be filtered reconstructed samples.

8. The method of claim 1 , wherein

the first reconstructed samples are generated by a deblocking filter; and

the method further comprises:

applying the constrained directional enhancement filter on the first reconstructed samples to generate intermediate reconstructed samples; and

combining the intermediate reconstructed samples with sample offsets generated by the non linear mapping based filter to generate the second reconstructed samples.

9. The method of claim 1 , further comprising:

clipping the to-be filtered reconstructed samples before the applying of the loop restoration filter.

10. The method of claim 9 , further comprising:

clipping intermediate reconstructed samples before a combination with sample offsets generated by the non linear mapping based filter.

11. An apparatus for video coding, comprising processing circuitry configured to:

buffer first boundary pixel values of a subset of first reconstructed samples at a first node along a loop filter chain, a non linear mapping based filter and a constrained directional enhancement filter being applied to the first boundary pixel values, the non linear mapping based filter and the constrained directional enhancement filter being applied in the loop filter chain before a loop restoration filter, the first boundary pixel values being values of pixels at a frame boundary;

buffer second boundary pixel values of a subset of second reconstructed samples at a second node along the loop filter chain, the second reconstructed samples at the second node being generated after at least one of the non linear mapping based filter or the constrained directional enhancement filter is applied to the loop filter chain, and the second boundary pixel values being values of the pixels at the frame boundary; and

apply the loop restoration filter on to-be filtered reconstructed samples based on the buffered first boundary pixel values of the subset of the first reconstructed samples and the buffered second boundary pixel values of the subset of the second reconstructed samples.

12. The apparatus of claim 11 , wherein the non linear mapping based filter is at least one of a cross-component sample offset (CCSO) filter and a local sample offset (LSO) filter.

13. The apparatus of claim 11 , wherein the first reconstructed samples at the first node are input of the non linear mapping based filter.

14. The apparatus of claim 13 , wherein

the second reconstructed samples at the second node are generated after an applying of sample offsets generated by the non linear mapping based filter.

15. The apparatus of claim 14 , wherein the processing circuitry is configured to:

combine the sample offsets generated by the non linear mapping based filter with output of the constrained directional enhancement filter to generate the second reconstructed samples.

16. The apparatus of claim 14 , wherein the processing circuitry is configured to:

combine the sample offsets generated by the non linear mapping based filter with the first reconstructed samples to generate intermediate reconstructed samples; and

apply the constrained directional enhancement filter to the intermediate reconstructed samples to generate the second reconstructed samples.

17. The apparatus of claim 13 , wherein the processing circuitry is configured to:

combine the second reconstructed samples at the second node with sample offsets generated by the non linear mapping based filter to generate the to-be filtered reconstructed samples.

18. The apparatus of claim 11 , wherein

the first reconstructed samples are generated by a deblocking filter; and

the processing circuitry is configured to:

apply the constrained directional enhancement filter on the first reconstructed samples to generate intermediate reconstructed samples; and

combine the intermediate reconstructed samples with sample offsets generated by the non linear mapping based filter to generate the second reconstructed samples.

19. The apparatus of claim 11 , wherein the processing circuitry is configured to:

clip the to-be filtered reconstructed samples before the applying of the loop restoration filter.

20. The apparatus of claim 19 , wherein the processing circuitry is configured to:

clip intermediate reconstructed samples before a combination with sample offsets generated by the non linear mapping based filter.