Use of header syntax elements and adaptation parameter set

1. A method of video processing, comprising:

performing a conversion between a video and a bitstream of the video according to a format rule, and

wherein the format rule specifies that a first syntax element specifying whether one or more chroma-related adaptation parameter set (APS) syntax elements are present in an APS syntax structure is included in the APS syntax structure,

wherein the first syntax element equal to 1 specifies that an APS network abstraction layer (NAL) unit is allowed to include the one or more chroma-related APS syntax elements and the first syntax element equal to 0 specifies that the APS NAL unit does not include the one or more chroma-related APS syntax elements,

wherein the APS NAL unit has APS parameters type equal to scaling list APS type, luma mapping with chroma scaling (LMCS) APS type, or adaptive loop filtering (ALF) APS type, and the one or more chroma-related APS syntax elements include scaling list chroma-related data syntax elements, LMCS chroma-related data syntax elements, or ALF chroma-related data syntax elements, and

wherein constraints on value of the first syntax element in different APS parameters types are different, wherein a one-way constraint of the first syntax element in the APS NAL unit with the LMCS APS type or the ALF APS type is applied and two-way constraints of the first syntax element in the APS NAL unit with the scaling list APS type are applied.

2. The method of claim 1 , wherein the one-way constraint specifies if a first certain condition is true, a first constraint of the first syntax element is applied, the two-way constraints specify if the first certain condition is true, the first constraint of the first syntax element is applied, otherwise a second constraint of the first syntax element is applied.

3. The method of claim 2 , wherein the one-way constraint or the two-way constraints of the first syntax element are based on a chroma format index.

4. The method of claim 1 , wherein when i) the APS NAL unit has the APS parameters type equal to the scaling list APS type, ii) the first syntax element is equal to 0, iii) a variable id is not equal to X and id % M is not equal to N, the scaling list chroma-related data syntax elements are excluded from the APS syntax structure, whereby X, M and N are integers.

5. The method of claim 4 , wherein X=27.

6. The method of claim 4 , wherein M=3, N=2.

7. The method of claim 1 , wherein when the APS NAL unit has the APS parameters type equal to the ALF APS type and the first syntax element is equal to 0, the ALF chroma-related data syntax elements are excluded from the APS syntax structure.

8. The method of claim 1 , wherein when the APS NAL unit has the APS parameters type equal to the LMCS APS type and the first syntax element is equal to 0, the LMCS chroma-related data syntax elements are excluded from the APS syntax structure.

9. The method of claim 1 , wherein the conversion includes encoding the video into the bitstream.

10. The method of claim 1 , wherein the conversion includes decoding the video from the bitstream.

11. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

perform a conversion between a video and a bitstream of the video according to a format rule,

wherein the format rule specifies that a first syntax element specifying whether one or more chroma-related adaptation parameter set (APS) syntax elements are present in an APS syntax structure is included in the APS syntax structure,

wherein the first syntax element equal to 1 specifies that an APS network abstraction layer (NAL) unit is allowed to include the one or more chroma-related APS syntax elements and the first syntax element equal to 0 specifies that the APS NAL unit does not include the one or more chroma-related APS syntax elements,

wherein the APS NAL unit has APS parameters type equal to scaling list APS type, luma mapping with chroma scaling (LMCS) APS type, or adaptive loop filtering (ALF) APS type, and the one or more chroma-related APS syntax elements include scaling list chroma-related data syntax elements, LMCS chroma-related data syntax elements, or ALF chroma-related data syntax elements, and

wherein constraints on value of the first syntax element in different APS parameters types are different, wherein a one-way constraint of the first syntax element in the APS NAL unit with the LMCS APS type or the ALF APS type is applied and two-way constraints of the first syntax element in the APS NAL unit with the scaling list APS type are applied.

12. The apparatus of claim 11 , wherein the one-way constraint specifies if a first certain condition is true, a first constraint of the first syntax element is applied; the two-way constraints specify if the first certain condition is true, the first constraint of the first syntax element is applied, otherwise a second constraint of the first syntax element is applied, and

wherein the one-way constraint or the two-way constraints of the first syntax element are based on a chroma format index.

13. The apparatus of claim 11 , wherein when i) the APS NAL unit has the APS parameters type equal to the scaling list APS type, ii) the first syntax element is equal to 0, iii) a variable id is not equal to X and id % M is not equal to N, the scaling list chroma-related data syntax elements are excluded from the APS syntax structure, whereby X, M and N are integers, and wherein X=27, M=3, and N=2.

14. The apparatus of claim 11 , wherein when the APS NAL unit has the APS parameters type equal to the ALF APS type and the first syntax element is equal to 0, the ALF chroma-related data syntax elements are excluded from the APS syntax structure.

15. The apparatus of claim 11 , wherein when the APS NAL unit has the APS parameters type equal to the LMCS APS type and the first syntax element is equal to 0, the LMCS chroma-related data syntax elements are excluded from the APS syntax structure.

16. A non-transitory computer-readable storage medium storing instructions that cause a processor to:

perform a conversion between a video and a bitstream of the video according to a format rule,

wherein the format rule specifies that a first syntax element specifying whether one or more chroma-related adaptation parameter set (APS) syntax elements are present in an APS syntax structure is included in the APS syntax structure,

wherein the first syntax element equal to 1 specifies that an APS network abstraction layer (NAL) unit is allowed to include the one or more chroma-related APS syntax elements and the first syntax element equal to 0 specifies that the APS NAL unit does not include the one or more chroma-related APS syntax elements,

wherein the APS NAL unit has APS parameters type equal to scaling list APS type, luma mapping with chroma scaling (LMCS) APS type, or adaptive loop filtering (ALF) APS type, and the one or more chroma-related APS syntax elements include scaling list chroma-related data syntax elements, LMCS chroma-related data syntax elements, or ALF chroma-related data syntax elements, and

wherein constraints on value of the first syntax element in different APS parameters types are different, wherein a one-way constraint of the first syntax element in the APS NAL unit with the LMCS APS type or the ALF APS type is applied and two-way constraints of the first syntax element in the APS NAL unit with the scaling list APS type are applied.

17. The non-transitory computer-readable storage medium of claim 16 , wherein the one-way constraint specifies if a first certain condition is true, a first constraint of the first syntax element is applied; the two-way constraints specify if the first certain condition is true, the first constraint of the first syntax element is applied, otherwise a second constraint of the first syntax element is applied, and

wherein the one-way constraint or the two-way constraints of the first syntax element are based on a chroma format index.

18. The non-transitory computer-readable storage medium of claim 16 , wherein when i) the APS NAL unit has the APS parameters type equal to the scaling list APS type, ii) the first syntax element is equal to 0, iii) a variable id is not equal to X and id % M is not equal to N, the scaling list chroma-related data syntax elements are excluded from the APS syntax structure, whereby X, M and N are integers, and wherein X=27, M=3, and N=2.

19. A method for storing a bitstream of a video comprising:

generating the bitstream of the video according to a format rule; and

storing the bitstream in a non-transitory computer-readable recording medium,

wherein the format rule specifies that a first syntax element specifying whether one or more chroma-related adaptation parameter set (APS) syntax elements are present in an APS syntax structure is included in the APS syntax structure,

wherein the first syntax element equal to 1 specifies that an APS network abstraction layer (NAL) unit is allowed to include the one or more chroma-related APS syntax elements and the first syntax element equal to 0 specifies that the APS NAL unit does not include the one or more chroma-related APS syntax elements,

wherein the APS NAL unit has APS parameters type equal to scaling list APS type, luma mapping with chroma scaling (LMCS) APS type, or adaptive loop filtering (ALF) APS type, and the one or more chroma-related APS syntax elements include scaling list chroma-related data syntax elements, LMCS chroma-related data syntax elements, or ALF chroma-related data syntax elements, and

wherein constraints on value of the first syntax element in different APS parameters types are different, wherein a one-way constraint of the first syntax element in the APS NAL unit with the LMCS APS type or the ALF APS type is applied and two-way constraints of the first syntax element in the APS NAL unit with the scaling list APS type are applied.

20. The method of claim 19 , wherein the one-way constraint specifies if a first certain condition is true, a first constraint of the first syntax element is applied; the two-way constraints specify if the first certain condition is true, the first constraint of the first syntax element is applied, otherwise a second constraint of the first syntax element is applied, and

wherein the one-way constraint or the two-way constraints of the first syntax element are based on a chroma format index.