Methods and devices for lossless coding modes in video coding

1. A method for decoding a video signal, comprising:

partitioning, at a decoder, a video picture into a plurality of coding units (CUs) comprising a lossless CU; and

receiving, at the decoder, a high-level syntax, wherein the high-level syntax comprises a first flag that indicates whether a residual coding scheme used by a CU in the CUs or by a coding block of a CU in the CUs is switchable between a residual coding scheme used by a non-transform skip mode and a residual coding scheme used by a transform skip mode.

2. The method of claim 1 , further comprising:

receiving, at the decoder and when the residual coding scheme is switchable, low-level syntax at CU level, wherein the low-level syntax comprises a residual coding scheme used by the lossless CU or a lossless coding block (CB).

3. The method of claim 1 , wherein the high-level syntax comprises a second flag that signals whether the residual coding scheme can be selected.

4. The method of claim 3 , further comprising:

applying, at the decoder and when the high-level syntax signals 0, a residual coding scheme used by a non-transform skip mode for the lossless CU or a lossless coding block (CB).

5. The method of claim 3 , further comprising:

receiving, at the decoder and when the high-level syntax signals 1, a low-level syntax to indicate which residual coding scheme is used for the lossless CU or a lossless coding block (CB).

6. The method of claim 1 , further comprising:

controlling, at the decoder and at a CU level, a decoder-side motion vector refinement (DMVR) based on a first predefined quantization parameter (QP) threshold.

7. The method of claim 6 , further comprising:

controlling, at the decoder and at the CU level, a bi-directional optical flow (BDOF) based on a second predefined quantization parameter (QP) threshold.

8. The method of claim 1 , further comprising:

acquiring, at the decoder, a residual block; and

applying, at the decoder, a residual rotation to the residual block after block differential pulse coded modulation (BDPCM) mode is applied to the plurality of CUs.

9. The method of claim 8 , wherein applying, at the decoder, the residual rotation to the residual block comprises:

applying, at the decoder and when a transform is not used, BDPCM mode to a prediction residual.

10. The method of claim 8 , further comprising:

applying, at the decoder, residual rotation only to a non-BDPCM block.

11. A computing device, comprising:

one or more processors; and

a non-transitory computer-readable storage medium storing instructions executable by the one or more processors, wherein the one or more processors are configured to:

partition a video picture into a plurality of coding units (CUs) comprising a lossless CU; and

receive a high-level syntax, wherein the high-level syntax comprises a first flag that indicates whether a residual coding scheme used by a CU in the CUs or by a coding block of a CU in the CUs is switchable between a residual coding scheme used by a non-transform skip mode and a residual coding scheme used by a transform skip mode.

12. The computing device of claim 11 , wherein the one or more processors are further configured to:

receive, when the residual coding scheme is switchable, low-level syntax at CU level, wherein the low-level syntax comprises a residual coding scheme used by the lossless CU or a lossless coding block (CB).

13. The computing device of claim 11 , wherein the high-level syntax comprises a second flag that signals whether the residual coding scheme can be selected.

14. The computing device of claim 13 , wherein the one or more processors are further configured to:

apply, when the high-level syntax signals 0, a residual coding scheme used by a non-transform skip mode for the lossless CU or a lossless coding block (CB).

15. The computing device of claim 13 , wherein the one or more processors are further configured to:

receive, when the high-level syntax signals 1, a low-level syntax to indicate which residual coding scheme is used for the lossless CU or a lossless coding block (CB).

16. A non-transitory computer-readable storage medium storing a plurality of programs for execution by a computing device having one or more processors, wherein the plurality of programs, when executed by the one or more processors, cause the computing device to perform acts comprising:

partitioning, at a decoder, a video picture into a plurality of coding units (CUs) comprising a lossless CU; and

receiving, at the decoder, a high-level syntax, wherein the high-level syntax comprises a first flag that indicates whether a residual coding scheme used by a CU in the CUs or by a coding block of a CU in the CUs is switchable between a residual coding scheme used by a non-transform skip mode and a residual coding scheme used by a transform skip mode.

17. The non-transitory computer-readable storage medium of claim 16 , wherein the plurality of programs further cause the computing device to perform:

receiving, at the decoder and when the residual coding scheme is switchable, low-level syntax at CU level, wherein the low-level syntax comprises a residual coding scheme used by the lossless CU or a lossless coding block (CB).

18. The non-transitory computer-readable storage medium of claim 16 , wherein the high-level syntax comprises a second flag that signals whether the residual coding scheme can be selected.

19. The non-transitory computer-readable storage medium of claim 18 , wherein the plurality of programs further cause the computing device to perform:

applying, at the decoder and when the high-level syntax signals 0, a residual coding scheme used by a non-transform skip mode for the lossless CU or a lossless coding block (CB).

20. The non-transitory computer-readable storage medium of claim 18 , wherein the plurality of programs further cause the computing device to perform:

receiving, at the decoder and when the high-level syntax signals 1, a low-level syntax to indicate which residual coding scheme is used for the lossless CU or a lossless coding block (CB).