Encoding or decoding method and apparatus

A decoding apparatus, the apparatus comprising:

• a first extracting unit, configured to extract first information in a bitstream;
• a first determining unit, configured to determine a chroma component intra prediction mode according to the first information extracted by the first extracting unit;
• a second extracting unit, configured to, when the first determining unit cannot determine the chroma component intra prediction mode according to the first information, extract second information in the bitstream;
• and
• a second determining unit, configured to determine the chroma component intra prediction mode according to the second information extracted by the second extracting unit, wherein
• the first information comprises information for indicating whether the chroma component intra prediction mode is a DM mode or an LM mode;
• and
• the second information is used to indicate a remaining mode of the chroma component intra prediction mode, wherein the remaining mode is one of available chroma component intra prediction modes other than a mode that may be determined according to the first information.