1. A method of processing video data, comprising: determining, during a conversion between a current chroma video block of a video and a bitstream of the video, that a scaling process is applied on chroma residual samples of the current chroma video block; and performing the conversion based on the determining, wherein in the scaling process, the chroma residual samples are scaled based on at least one scaling factor before being used to reconstruct the current chroma video block; and wherein one or more chroma video blocks within a video region comprising the current chroma video block share the same at least one scaling factor in the scaling process; wherein the at least one scaling factor is derived by following: checking an availability of each of one or more neighboring luma blocks of a video unit of the video which determined based on a luma sample corresponding to a top-left sample of the current chroma video block; determining, based on the availability of the each of the one or more neighboring luma blocks, whether to retrieve neighboring luma samples of the video unit, wherein the neighboring luma samples located in predefined positions neighboring to the video unit; and deriving the at least one scaling factor based on an averaged luma variable computed using the neighboring luma samples by an average operation in case that at least one of the one or more neighboring luma blocks is available, and wherein in response to the one or more neighboring luma blocks being determined to be unavailable, the at least one scaling factor is derived by setting the averaged luma variable equal to a default value, and wherein the default value equals to 1<<(bitDepth−1), where bitDepth is a bit depth of the video.
2. The method of claim 1 , wherein the one or more chroma video blocks in the video region corresponds to all chroma video blocks in the video region which apply the scaling process.
3. The method of claim 1 , wherein the video region is a virtual pipeline data unit.
4. The method of claim 1 , wherein the neighboring luma samples include at least one of one or more left neighboring sample columns or one or more above neighboring sample rows of the video unit.
5. The method of claim 4 , wherein a total number of the neighboring luma samples is depends on a size information of the video region.
6. The method of claim 1 , wherein the scaling process is based on a piecewise linear model, and wherein an index identifying a piece to which the averaged luma variable belongs, and the at least one scaling factor is derived based on the index.
7. The method of claim 1 , wherein a syntax element indicative of enabling or disabling the scaling process below a picture level is conditionally included at the picture level associated with the current chroma video block, and wherein in response to a value of the syntax element being equal to one, the application of the scaling process below the picture level is enabled, and in response to the value of the syntax element being equal to zero, the application of the scaling process below the picture level is disabled.
8. The method of claim 1 , wherein the conversion includes encoding the current chroma video block into the bitstream.
9. The method of claim 1 , wherein the conversion includes decoding the current chroma video block 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, during a conversion between a current chroma video block of a video and a bitstream of the video, that a scaling process is applied on chroma residual samples of the current chroma video block; and perform the conversion based on the determining, wherein in the scaling process, the chroma residual samples are scaled based on at least one scaling factor before being used to reconstruct the current chroma video block; and wherein one or more chroma video blocks within a video region comprising the current chroma video block share the same at least one scaling factor in the scaling process; wherein the at least one scaling factor is derived by following: checking an availability of each of one or more neighboring luma blocks of a video unit of the video which determined based on a luma sample corresponding to a top-left sample of the current chroma video block; determining, based on the availability of the each of the one or more neighboring luma blocks, whether to retrieve neighboring luma samples of the video unit, wherein the neighboring luma samples located in predefined positions neighboring to the video unit; and deriving the at least one scaling factor based on an averaged luma variable computed using the neighboring luma samples by an average operation in case that at least one of the one or more neighboring luma blocks is available, and wherein in response to the one or more neighboring luma blocks being determined to be unavailable, the at least one scaling factor is derived by setting the averaged luma variable equal to a default value, and wherein the default value equals to 1<<(bitDepth−1), where bitDepth is a bit depth of the video.
11. The apparatus of claim 10 , wherein the one or more chroma video blocks in the video region corresponds to all chroma video blocks in the video region which apply the scaling process; and wherein the video region is a virtual pipeline data unit.
12. The apparatus of claim 10 , wherein the neighboring luma samples include at least one of one or more left neighboring sample columns or one or more above neighboring sample rows of the video unit; wherein a total number of the neighboring luma samples is depends on a size information of the video region; wherein the scaling process is based on a piecewise linear model, and wherein an index identifying a piece to which the averaged luma variable belongs, and the at least one scaling factor is derived based on the index; wherein a syntax element indicative of enabling or disabling the scaling process below a picture level is conditionally included at the picture level associated with the current chroma video block, and wherein in response to a value of the syntax element being equal to one, the application of the scaling process below the picture level is enabled, and in response to the value of the syntax element being equal to zero, the application of the scaling process below the picture level is disabled.
13. A non-transitory computer-readable storage medium storing instructions that cause a processor to: determine, during a conversion between a current chroma video block of a video and a bitstream of the video, that a scaling process is applied on chroma residual samples of the current chroma video block; and perform the conversion based on the determining, wherein in the scaling process, the chroma residual samples are scaled based on at least one scaling factor before being used to reconstruct the current chroma video block; and wherein one or more chroma video blocks within a video region comprising the current chroma video block share the same at least one scaling factor in the scaling process; wherein the at least one scaling factor is derived by following: checking an availability of each of one or more neighboring luma blocks of a video unit of the video which determined based on a luma sample corresponding to a top-left sample of the current chroma video block; determining, based on the availability of the each of the one or more neighboring luma blocks, whether to retrieve neighboring luma samples of the video unit, wherein the neighboring luma samples located in predefined positions neighboring to the video unit; and deriving the at least one scaling factor based on an averaged luma variable computed using the neighboring luma samples by an average operation in case that at least one of the one or more neighboring luma blocks is available, and wherein in response to the one or more neighboring luma blocks being determined to be unavailable, the at least one scaling factor is derived by setting the averaged luma variable equal to a default value, and wherein the default value equals to 1<<(bitDepth−1), where bitDepth is a bit depth of the video.
14. The non-transitory computer-readable storage medium of claim 13 , wherein the one or more chroma video blocks in the video region corresponds to all chroma video blocks in the video region which apply the scaling process; and wherein the video region is a virtual pipeline data unit.
15. The non-transitory computer-readable storage medium of claim 13 , wherein the neighboring luma samples include at least one of one or more left neighboring sample columns or one or more above neighboring sample rows of the video unit; wherein a total number of the neighboring luma samples is depends on a size information of the video region; wherein the scaling process is based on a piecewise linear model, and wherein an index identifying a piece to which the averaged luma variable belongs, and the at least one scaling factor is derived based on the index; wherein a syntax element indicative of enabling or disabling the scaling process below a picture level is conditionally included at the picture level associated with the current chroma video block, and wherein in response to a value of the syntax element being equal to one, the application of the scaling process below the picture level is enabled, and in response to the value of the syntax element being equal to zero, the application of the scaling process below the picture level is disabled.
16. 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 that a scaling process is applied on chroma residual samples of a current chroma video block of the video; and generating the bitstream based on the determining, wherein in the scaling process, the chroma residual samples are scaled based on at least one scaling factor before being used to reconstruct the current chroma video block; and wherein one or more chroma video blocks within a video region comprising the current chroma video block share the same at least one scaling factor in the scaling process; wherein the at least one scaling factor is derived by following: checking an availability of each of one or more neighboring luma blocks of a video unit of the video which determined based on a luma sample corresponding to a top-left sample of the current chroma video block; determining, based on the availability of the each of the one or more neighboring luma blocks, whether to retrieve neighboring luma samples of the video unit, wherein the neighboring luma samples located in predefined positions neighboring to the video unit; and deriving the at least one scaling factor based on an averaged luma variable computed using the neighboring luma samples by an average operation in case that at least one of the one or more neighboring luma blocks is available, and wherein in response to the one or more neighboring luma blocks being determined to be unavailable, the at least one scaling factor is derived by setting the averaged luma variable equal to a default value, and wherein the default value equals to 1<<(bitDepth−1), where bitDepth is a bit depth of the video.
17. The non-transitory computer-readable storage medium of claim 16 , wherein the one or more chroma video blocks in the video region corresponds to all chroma video blocks in the video region which apply the scaling process; and wherein the video region is a virtual pipeline data unit.
18. The non-transitory computer-readable storage medium of claim 16 , wherein the neighboring luma samples include at least one of one or more left neighboring sample columns or one or more above neighboring sample rows of the video unit; wherein a total number of the neighboring luma samples is depends on a size information of the video region; wherein the scaling process is based on a piecewise linear model, and wherein an index identifying a piece to which the averaged luma variable belongs, and the at least one scaling factor is derived based on the index; wherein a syntax element indicative of enabling or disabling the scaling process below a picture level is conditionally included at the picture level associated with the current chroma video block, and wherein in response to a value of the syntax element being equal to one, the application of the scaling process below the picture level is enabled, and in response to the value of the syntax element being equal to zero, the application of the scaling process below the picture level is disabled.
