Quantization properties of adaptive in-loop color-space transform for video coding

1. A method of processing video data, comprising:

determining, for a conversion between a video comprising a current video block and a bitstream of the video, that a first coding tool is used based on a rule for the current video block; and

performing the conversion according to the determining,

wherein the first coding tool includes transforming a representation of a visual signal between two color spaces; and

wherein the rule specifies that a first quantization parameter offset for a luma channel of the current video block is equal to K1 and a second quantization parameter offset for a first chroma channel of the current video block is K1+O, whereby K1 and O are integers, wherein K1 is −5 and O is 6.

2. The method of claim 1 , wherein a third quantization parameter offset for a second chroma channel of the current video block is equal to 3.

3. The method of claim 1 , wherein the rule further specifies to use a same lowest allowed quantization parameter for all video blocks coded using a transform skip mode of the video.

4. The method of claim 3 , wherein the lowest allowed quantization parameter is independent of whether the first coding tool is applied or not to a video block coded using the transform skip mode.

5. The method of claim 1 , wherein the rule further specifies that the first quantization parameter offset for the luma channel of the current video block or the second quantization parameter offset for the first chroma channel of the current video block is added before a quantization parameter being clipped to a given range.

6. The method of claim 1 , wherein the current video block is in any color spaces including a YCoCg color space, a YCbCr color space or a YCoCg-R color space.

7. The method of claim 1 , wherein when the current video block is in a YCgCo or a YCgCo-R color space, the first chroma channel is a Cg channel.

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

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

10. 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:

determine, for a conversion between a video comprising a current video block and a bitstream of the video, that a first coding tool is used based on a rule for the current video block; and

perform the conversion according to the determination,

wherein the first coding tool includes transforming a representation of a visual signal between two color spaces; and

wherein the rule specifies that a first quantization parameter offset for a luma channel of the current video block is equal to K1 and a second quantization parameter offset for a first chroma channel of the current video block is K1+O, whereby K1 and O are integers, wherein K1 is −5 and O is 6.

11. The apparatus of claim 10 ,

wherein a third quantization parameter offset for a second chroma channel of the current video block is equal to 3.

12. The apparatus of claim 10 , wherein the rule further specifies to use a same lowest allowed quantization parameter for all video blocks coded using a transform skip mode of the video;

wherein the lowest allowed quantization parameter is independent of whether the first coding tool is applied or not to a video block coded using the transform skip mode; and

wherein the rule further specifies that the first quantization parameter offset for the luma channel of the current video block or the second quantization parameter offset for the first chroma channel of the current video block is added before a quantization parameter being clipped to a given range.

13. The apparatus of claim 10 , wherein the current video block is in any color spaces including a YCoCg color space, a YCbCr color space or a YCoCg-R color space; and

wherein when the current video block is in a YCgCo or a YCgCo-R color space, the first chroma channel is a Cg channel.

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

determine, for a conversion between a video comprising a current video block and a bitstream of the video, that a first coding tool is used based on a rule for the current video block; and

perform the conversion according to the determination,

wherein the first coding tool includes transforming a representation of a visual signal between two color spaces; and

wherein the rule specifies that a first quantization parameter offset for a luma channel of the current video block is equal to K1 and a second quantization parameter offset for a first chroma channel of the current video block is K1+O, whereby K1 and O are integers, wherein K1 is −5 and O is 6.

15. The non-transitory computer-readable storage medium of claim 14 ,

wherein a third quantization parameter offset for a second chroma channel of the current video block is equal to 3.

16. The non-transitory computer-readable storage medium of claim 14 , wherein the rule further specifies to use a same lowest allowed quantization parameter for all video blocks coded using a transform skip mode of the video;

wherein the lowest allowed quantization parameter is independent of whether the first coding tool is applied or not to a video block coded using the transform skip mode;

wherein the rule further specifies that the first quantization parameter offset for the luma channel of the current video block or the second quantization parameter offset for the first chroma channel of the current video block is added before a quantization parameter being clipped to a given range;

wherein the current video block is in any color spaces including a YCoCg color space, a YCbCr color space or a YCoCg-R color space; and

wherein when the current video block is in a YCgCo or a YCgCo-R color space, the first chroma channel is a Cg channel.

17. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:

determining, for a video comprising a current video block, that a first coding tool is used based on a rule for the current video block; and

generating the bitstream according to the determining,

wherein the first coding tool includes transforming a representation of a visual signal between two color spaces; and

wherein the rule specifies that a first quantization parameter offset for a luma channel of the current video block is equal to K1 and a second quantization parameter offset for a first chroma channel of the current video block is K1+O, whereby K1 and O are integers, wherein K1 is −5 and O is 6.

18. The non-transitory computer-readable recording medium of claim 17 ,

wherein a third quantization parameter offset for a second chroma channel of the current video block is equal to 3.

19. The non-transitory computer-readable recording medium of claim 17 , wherein the rule further specifies to use a same lowest allowed quantization parameter for all video blocks coded using a transform skip mode of the video;

wherein the lowest allowed quantization parameter is independent of whether the first coding tool is applied or not to a video block coded using the transform skip mode;

wherein the rule further specifies that the first quantization parameter offset for the luma channel of the current video block or the second quantization parameter offset for the first chroma channel of the current video block is added before a quantization parameter being clipped to a given range;

wherein the current video block is in any color spaces including a YCoCg color space, a YCbCr color space or a YCoCg-R color space; and

wherein when the current video block is in a YCgCo or a YCgCo-R color space, the first chroma channel is a Cg channel.