Method and apparatus for lossless coding of video data

1. A video processing method, comprising:

receiving a bitstream comprising a plurality of coding tree unit (CTUs) in a picture;

determining whether lossless coding is applied to the plurality of CTUs, based on a plurality of flags, respectively,

wherein the plurality of flags comprise a first flag associated with a first CTU and each of the plurality of flags is a CTU level lossless flag, and the method further comprises:

in response to a determination that lossless coding is applied to the first CTU, performing lossless coding to the first CTU.

2. The method of claim 1 , further comprising:

in response to the first flag being not signaled in the bitstream, determining that lossy coding is applied to the first CTU.

3. The method of claim 1 , further comprising:

in response to the determination that lossless coding is applied to the first CTU, determining, based on a second flag, a residual coding method applied to transform blocks of the first CTU.

4. The method of claim 3 , further comprising:

in response to the second flag having a first value, determining that a first residual coding method is applied to the transform blocks.

5. The method of claim 3 , further comprising:

in response to the second flag having a second value, determining a value of a third flag; and

in response to the third flag having a third value, determining that a first residual coding method is applied to the transform blocks, or

in response to the third flag having a fourth value, determining that a second residual coding method is applied to the transform blocks.

6. The method of claim 1 , further comprising:

in response to the determination that lossless coding is applied to the first CTU, coding the first CTU in a transform skip mode regardless of whether a transform-skip flag for the first CTU is signaled in the bitstream.

7. The method of claim 1 , further comprising:

determining, based on a fourth flag, whether the first flag is signaled in the bitstream, the fourth flag being a sequence parameter sets (SPS) level flag.

8. The method of claim 7 , further comprising:

in response to the fourth flag being not signaled in the bitstream, determining that the bitstream does not comprise the first flag.

9. The method of claim 1 , further comprising:

in response to a fifth flag having a fifth value, determining that lossless coding is applied to a picture slice including the first CTU; or

in response to the fifth flag having a sixth value, determining that the first flag is signaled in the bitstream,

wherein the fifth flag is a slice level lossless flag.

10. The method of claim 9 , further comprising:

in response to a sixth flag having a seventh value, determining that lossless coding is applied to a picture including the first CTU; or

in response to the sixth flag having an eighth value, determining that the fifth flag is signaled in the bitstream,

wherein the sixth flag is a picture level lossless flag.

11. The method of claim 10 , further comprising:

in response to a seventh flag having a ninth value, determining that lossless coding is applied to a picture associated with a picture parameter sets (PPS) and including the first CTU; or

in response to the seventh flag having a tenth value, determining that the sixth flag is signaled in the bitstream,

wherein the seventh flag is a PPS level lossless flag.

12. The method of claim 1 , further comprising:

in response to an eighth flag having an eleventh value, determining that lossless coding is applied to a picture associated with a SPS and including the first CTU; or

in response to the eighth flag having a twelfth value, determining that lossy coding is applied to one or more CTUs associated with the SPS,

wherein the eighth flag is a SPS level lossless flag.

13. The method of claim 1 , further comprising:

in response to the determination that lossless coding is applied to the first CTU, disabling, for the first CTU, one or more of:

a de-blocking filtering process;

a sample adaptive offset (SAO) process;

an adaptive loop filter (ALF) process;

luma mapping with chroma scaling (LMCS);

luma dependent chroma residual scaling process;

sub block transform (SBT);

signaling of Multiple Transform Selection (MTS) index;

signaling of low-frequency non-separable transform (LFNST) index;

a joint Cb-Cr mode; or

an Intra Subpartition (ISP) mode.

14. A video processing apparatus, comprising:

at least one memory for storing instructions; and

at least one processor configured to execute the instructions to cause the apparatus to perform:

receiving a bitstream comprising a plurality of coding tree unit (CTUs) in a picture;

determining whether lossless coding is applied to the plurality of CTUs, based on a plurality of flags, respectively,

wherein the plurality of flags comprise a first flag associated with a first CTU and each of the plurality of flags is a CTU level lossless flag, and the method further comprises:

in response to a determination that lossless coding is applied to the first CTU, performing lossless coding to the first CTU.

15. A non-transitory computer readable storage medium storing a set of instructions that are executable by one or more processing devices to cause a video processing apparatus to perform a method comprising:

receiving a bitstream comprising a plurality of coding tree unit (CTUs) in a picture;

determining whether lossless coding is applied to the plurality of CTUs, based on a plurality of flags, respectively,

wherein the plurality of flags comprise a first flag associated with a first CTU and each of the plurality of flags is a CTU level lossless flag, and the method further comprises:

in response to a determination that lossless coding is applied to the first CTU, performing lossless coding to the first CTU.

16. The non-transitory computer readable storage medium of claim 15 , wherein the set of instructions are executable by the one or more processing devices to cause the video processing apparatus to perform:

in response to the first flag being not signaled in the bitstream, determining that lossy coding is applied to the first CTU.