Method and apparatus for chroma intra prediction in video coding

A device, comprising:

• one or more processors;
• and
• a computer-readable storage medium coupled to the one or more processors and storing instructions, which when executed by the one or more processors, cause the device to:
• obtain an initial intra prediction mode X of a chroma component based on a value of a luma intra prediction mode (intraPredModeY) of a luma component by using a first look up table (LUT);
• a chroma intra prediction mode Y is equal to the initial intra prediction mode X of the chroma component when one of the following is true:
• SubWidthC is equal to SubHeightC,
• X is smaller than 2,
• X is larger than 66;
• otherwise, a chroma intra prediction mode Y is derived from a second LUT by using the initial intra prediction mode X of the chroma component, wherein SubWidthC and SubHeightC denote the chroma component in horizontal and vertical directions respectively, wherein the value 66 indicates a 45° angle mode;
• obtain an intraPredAngle parameter for the chroma component based on the chroma intra prediction mode Y;
• obtain array of reference samples for the chroma component;
• and
• obtain predicted samples of the chroma component using the array of reference samples and the intraPredAngle parameter.

A non-transitory computer-readable storage medium storing a bitstream that, when decoded by a coding device, is used by the coding device to generate a video, wherein the bitstream is generated by:

• obtaining an initial intra prediction mode X of chroma component based on a value of a luma intra prediction mode (intraPredModeY) of a luma component by using a first look up table (LUT);
• a chroma intra prediction mode Y is equal to the initial intra prediction mode X of the chroma component when one of the following is true:
• SubWidthC is equal to SubHeightC,
• X is smaller than 2,
• X is larger than 66;
• otherwise, a chroma intra prediction mode Y is derived from a second LUT by using the initial intra prediction mode X of the chroma component, wherein SubWidthC and SubHeightC denote the chroma component in horizontal and vertical directions respectively, wherein the value 66 indicates a 45° angle mode;
• obtaining an intraPredAngle parameter for the chroma component based on the chroma intra prediction mode Y;
• obtaining array of reference samples for the chroma component;
• and
• obtaining predicted samples of the chroma component using the array of reference samples and the intraPredAngle parameter.