Adaptive colour transform related signalling for both of CU level and TU level

1. A method for video coding performed by at least one processor, the method comprising:

obtaining video data;

obtaining a coding unit (CU) block of the video data;

determining whether a flag of the CU block is set to a predetermined flag condition;

determining whether a tree type of the CU block is set to a predetermined tree type;

determining whether to signal an adaptive color transform (ACT) flag based on both of whether the flag of the CU block is set to the predetermined flag condition and whether the tree type of the CU block is set to the predetermined tree type; and

coding the video data based on a whether the ACT flag is signaled.

2. The method according to claim 1 , wherein determining whether to signal the ACT flag is based on only whether the flag of the CU block is set to the predetermined flag condition.

3. The method according to claim 1 , wherein the predetermined tree type indicates a single tree type, and wherein the predetermined flag condition comprises sps_act_enabled_flag being equal to 1.

4. The method according to claim 1 , wherein determining whether to signal an adaptive color transform (ACT) flag is implemented regardless of whether a prediction mode of the CU is an intra mode.

5. The method according to claim 1 , further comprises determining whether transform unit (TU) coded flags are both zero and whether the CU is coded with an ACT mode.

6. The method according to claim 5 , wherein the TU coded flags are flags of chrominance channels.

7. The method according to claim 6 , further comprising:

determining a TU coded flag of luminance is to be inferred to be 1 based on determining that the TU coded flags are both zero and that the CU is coded with the ACT mode.

8. The method according to claim 7 , wherein determining the TU coded flag of luminance is to be inferred to be 1 is implemented regardless of whether a prediction mode of the CU is an intra mode.

9. The method according to claim 8 , wherein coding the video data is further based on determining whether the TU coded flag of luminance is to be inferred to be 1.

10. An apparatus for video coding performed by at least one processor, the apparatus comprising:

at least one memory configured to store computer program code;

at least one processor configured to access the computer program code and operate as instructed by the computer program code, the computer program code including:

first obtaining code configured to cause the at least one processor to obtain video data;

second obtaining code configured to cause the at least one processor to obtain a coding unit (CU) block of the video data;

first determining code configured to cause the at least one processor to determine whether a flag of the CU block is set to a predetermined flag condition;

second determining code configured to cause the at least one processor to determine whether a tree type of the CU block is set to a predetermined tree type;

third determining code configured to cause the at least one processor to determine whether to signal an adaptive color transform (ACT) flag based on both of whether the flag of the CU block is set to the predetermined flag condition and whether the tree type of the CU block is set to the predetermined tree type; and

coding code configured to cause the at least one processor to code the video data based on a whether the ACT flag is signaled.

11. The apparatus according to claim 10 , wherein determining whether to signal the ACT flag is based on only whether the flag of the CU block is set to the predetermined flag condition.

12. The apparatus according to claim 10 , wherein the predetermined tree type indicates a single tree type, and wherein the predetermined flag condition comprises sps_act_enabled_flag being equal to 1.

13. The apparatus according to claim 10 , wherein determining whether to signal an adaptive color transform (ACT) flag is implemented regardless of whether a prediction mode of the CU is an intra mode.

14. The apparatus according to claim 10 , further comprising fourth determining code configured to cause the at least one processor to determine whether transform unit (TU) coded flags are both zero and whether the CU is coded with an ACT mode.

15. The apparatus according to claim 14 , wherein the TU coded flags are flags of chrominance channels.

16. The apparatus according to claim 15 , further comprising:

fifth determining code configured to cause the at least one processor to determine whether a TU coded flag of luminance is to be inferred to be 1 based on determining that the TU coded flags are both zero and that the CU is coded with the ACT mode.

17. The apparatus according to claim 16 , wherein determining the TU coded flag of luminance is to be inferred to be 1 is implemented regardless of whether a prediction mode of the CU is an intra mode.

18. A non-transitory computer readable medium storing a program causing a computer to execute a process, the process comprising:

obtaining video data;

obtaining a coding unit (CU) block;

determining whether a flag of the CU block is set to a predetermined flag condition;

determining whether a tree type of the CU block is set to a predetermined tree type;

determining whether to signal an adaptive color transform (ACT) flag based on both of whether the flag of the CU block is set to the predetermined flag condition and whether the tree type of the CU block is set to the predetermined tree type; and

coding the video data based on a whether the ACT flag is signaled.