Syntax element for chroma residual scaling

Abstract

A method for visual media processing includes processing a bitstream representation for a conversion between a current video block in a video region of a visual media data and the bitstream representation. The bitstream representation is based on a rule that specifies that one or more syntax elements used in a luma-dependent chroma residual scaling step are selectively included in the bitstream representation. The luma-dependent chroma residual scaling step includes scaling chroma samples based on neighboring reconstructed luma samples during the conversion. The one or more syntax elements are usable to derive a chroma residual scaling factor used for the scaling.

What is claimed is: 
     
         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 by applying the scaling process on the chroma residual samples,   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 multiple syntax elements and a bin index identifying a piece of a piecewise linear model are used to derive the at least one scaling factor, and the one or multiple syntax elements are conditionally included in the bitstream.   
     
     
         2 . The method of  claim 1 , wherein a value of the bin index is in a range of k0 to k1, where k0 and k1 are integers. 
     
     
         3 . The method of  claim 2 , wherein the value of the bin index is in a range of 0 to 15. 
     
     
         4 . The method of  claim 1 , wherein the bin index is derived based on an averaged luma variable computed based on neighboring luma samples of a video unit of a video region of the video which covers a luma sample corresponding to a top-left sample of the current chroma video block. 
     
     
         5 . The method of  claim 4 , wherein the bin index is derived by:
 checking an availability of one or more neighboring luma blocks of the video unit;   determining, based on the availability of the one or more neighboring luma blocks, whether to retrieve the neighboring luma samples of the video unit, wherein the one or more neighboring luma blocks comprise the neighboring luma samples; and   deriving the bin index based on the averaged luma variable computed using the neighboring luma samples by a rounding-based average operation in case that the neighboring luma samples are available.   
     
     
         6 . The method of  claim 5 , wherein in the checking the availability of the one or more neighboring luma blocks of the video unit, in response to a first neighboring luma block of the one or more neighboring luma blocks and the video unit being located in different video regions, the first neighboring luma block is treated as unavailable, and wherein the video region include at least one of a coding tree unit or a coding tree unit row. 
     
     
         7 . The method of  claim 1 , wherein the one or more syntax elements are included in an adaptation parameter set in the bitstream. 
     
     
         8 . The method of  claim 7 , wherein a syntax element indicative of selectively enabling or disabling the scaling process, if included in the bitstream, is included in a picture level associated with the current chroma video block. 
     
     
         9 . The method of  claim 1 , wherein the one or multiple syntax elements are used to present a luma value for each piece of the piecewise linear model. 
     
     
         10 . The method of  claim 1 , wherein the one or multiple syntax elements are used to present a luma value added to a representation of each piece of the piecewise linear model. 
     
     
         11 . The method of  claim 1 , wherein the one or multiple syntax elements are included in the bitstream in a case that a color format of the video is not 4:0:0. 
     
     
         12 . The method of  claim 1 , wherein the conversion includes encoding the current chroma video block into the bitstream. 
     
     
         13 . The method of  claim 1 , wherein the conversion includes decoding the current chroma video block from the bitstream. 
     
     
         14 . 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 by applying the scaling process on the chroma residual samples,   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 multiple syntax elements and a bin index identifying a piece of a piecewise linear model are used to derive the at least one scaling factor, and the one or multiple syntax elements are conditionally included in the bitstream.   
     
     
         15 . The apparatus of  claim 14 , wherein a value of the bin index is in a range of k0 to k1, where k0 and k1 are integers. 
     
     
         16 . The apparatus of  claim 15 , wherein the value of the bin index is in a range of 0 to 15. 
     
     
         17 . The apparatus of  claim 14 , wherein the bin index is derived based on an averaged luma variable computed based on neighboring luma samples of a video unit of a video region of the video which covers a luma sample corresponding to a top-left sample of the current chroma video block. 
     
     
         18 . The apparatus of  claim 17 , wherein the bin index is derived by:
 checking an availability of one or more neighboring luma blocks of the video unit;   determining, based on the availability of the one or more neighboring luma blocks, whether to retrieve the neighboring luma samples of the video unit, wherein the one or more neighboring luma blocks comprise the neighboring luma samples; and   deriving the bin index based on the averaged luma variable computed using the neighboring luma samples by a rounding-based average operation in case that the neighboring luma samples are available.   
     
     
         19 . 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 by applying the scaling process on the chroma residual samples,   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 multiple syntax elements and a bin index identifying a piece of a piecewise linear model are used to derive the at least one scaling factor, and the one or multiple syntax elements are conditionally included in the bitstream.   
     
     
         20 . 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 current chroma video block of the video, that a scaling process is applied on chroma residual samples of the current chroma video block; and   generating the bitstream by applying the scaling process on the chroma residual samples,   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 multiple syntax elements and a bin index identifying a piece of a piecewise linear model are used to derive the at least one scaling factor, and the one or multiple syntax elements are conditionally included in the bitstream.