Signaling of chroma and luma syntax elements in video coding

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, based on a chroma format of a video comprising a region, whether one or more first syntax flags applicable to the region of the video are absent in a bitstream of the video, wherein the one or more syntax flags are indicative of usage of a first coding step for the region, wherein the first coding step is a chroma scaling process applied to a chroma residue in which a scaling coefficient is derived based on reconstructed luma samples;
• and
• perform a conversion between the region of the video and the bitstream based on a presence or an absence of the one or more first syntax flags,
• wherein the one or more first syntax flags are absent in the bitstream in case the chroma format is 4:0:0.

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

• determine, based on a chroma format of a video comprising a region, whether one or more first syntax flags applicable to the region of the video are absent in a bitstream of the video, wherein the one or more syntax flags are indicative of usage of a first coding step for the region, wherein the first coding step is a chroma scaling process applied to a chroma residue in which a scaling coefficient is derived based on reconstructed luma samples;
• and
• perform a conversion between the region of the video and the bitstream based on a presence or an absence of the one or more first syntax flags,
• wherein the one or more first syntax flags are absent in the bitstream in case the chroma format is 4:0:0.

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, based on a chroma format of a video comprising a region, whether one or more first syntax flags applicable to the region of the video are absent in a bitstream of the video, wherein the one or more syntax flags are indicative of usage of a first coding step for the region, wherein the first coding step is a chroma scaling process applied to a chroma residue in which a scaling coefficient is derived based on reconstructed luma samples;
• and
• generating the bitstream based on a presence or an absence of the one or more first syntax flags,
• wherein the one or more first syntax flags are absent in the bitstream in case the chroma format is 4:0:0.