Parameter derivation in cross component mode

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 first chroma video block of a video and a bitstream of the video, that a scaling process is applied on chroma residual samples of the first 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 first chroma video block,
• wherein the at least one scaling factor 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 is determined based on a luma sample corresponding to a top-left sample of the first chroma video block,
• wherein the determining that the scaling process is applied on the chroma residual samples of the first chroma video block is based on a syntax element indicative of selectively enabling or disabling the scaling process in the bitstream of the video when included, wherein in response to the scaling process being enabled, the scaling process is applied on the chroma residual samples based on the at least one scaling factor,
• wherein in response to the scaling process being disabled, the scaling process refrains from being applied on the chroma residual samples, and
• wherein the syntax element, when included in the bitstream, is included in a picture level associated with a current video block.

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

• determine, during a conversion between a first chroma video block of a video and a bitstream of the video, that a scaling process is applied on chroma residual samples of the first 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 first chroma video block,
• wherein the at least one scaling factor 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 is determined based on a luma sample corresponding to a top-left sample of the first chroma video block,
• wherein the determining that the scaling process is applied on the chroma residual samples of the first chroma video block is based on a syntax element indicative of selectively enabling or disabling the scaling process in the bitstream of the video when included, wherein in response to the scaling process being enabled, the scaling process is applied on the chroma residual samples based on the at least one scaling factor,
• wherein in response to the scaling process being disabled, the scaling process refrains from being applied on the chroma residual samples, and
• wherein the syntax element, when included in the bitstream, is included in a picture level associated with a current video block.

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 first 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 first chroma video block,
• wherein the at least one scaling factor 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 is determined based on a luma sample corresponding to a top-left sample of the first chroma video block,
• wherein the determining that the scaling process is applied on the chroma residual samples of the first chroma video block is based on a syntax element indicative of selectively enabling or disabling the scaling process in the bitstream of the video when included, wherein in response to the scaling process being enabled, the scaling process is applied on the chroma residual samples based on the at least one scaling factor,
• wherein in response to the scaling process being disabled, the scaling process refrains from being applied on the chroma residual samples, and
• wherein the syntax element, when included in the bitstream, is included in a picture level associated with a current video block.