Chroma Presence Signaling for Conditional LMCS and CC-ALF Decoding

The patent applies preliminary action by defining a chroma_present_flag syntax element in advance at the sequence parameter set level. This flag pre-indicates whether chroma components are present and coded independently, allowing decoders to prepare appropriate processing paths before actual decoding occurs. The flag is set to 1 when chroma and luma are coded independently, enabling the decoder to activate chroma-specific tools like LMCS and CC-ALF only when needed, thus improving compression efficiency while controlling complexity through conditional processing.

The patent implements partial action by conditionally decoding chroma-related coding tools based on the chroma_present_flag value. When the flag indicates chroma components are present and independently coded, the decoder processes LMCS and CC-ALF tools to ensure high chroma quality. When the flag indicates chroma is not independently coded, these tools are skipped entirely. This selective approach ensures chroma coding quality is maintained only when necessary, reducing bitrate by avoiding redundant syntax element transmission and processing.

The patent applies universality by defining the chroma_present_flag at the sequence parameter set level, which serves multiple functions: it indicates chroma component presence, determines independent coding status, and controls activation of various chroma-related tools (LMCS, CC-ALF, BDPCM). This single syntax element provides multi-functional control across different coding scenarios and chroma formats (4:4:4, 4:2:2, 4:2:0), improving adaptability while reducing overall complexity by avoiding redundant flags at picture parameter set and slice levels.