Encoder, a decoder and corresponding methods related to intra prediction mode

A device for obtaining chroma intra prediction mode, comprising:

• one or more processors;
• and
• a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the device to:
• obtain first indication information for a luma position (cbWidth/2, cbHeight/2) of a current coding block, relative to a top-left luma sample postion (xCb, yCb) of the current coding block, wherein cbWidth represents a width of the current coding block in a luma component, cbHeight represents a height of the current coding block in the luma component;
• set a value of a luma intra prediction mode associated with the current coding block to a first default value, when the first indication information indicates that a Matrix-based Intra Prediction, MIP, is applied for the luma component at the luma position (cbWidth/2, cbHeight/2), relative to the top-left luma sample postion (xCb, yCb) of the current coding block;
• obtain second indication information for the luma position (cbWidth/2, cbHeight/2) of the current coding block, when the first indication information indicates that the MIP is not applied for the luma component at the luma position (cbWidth/2, cbHeight/2), relative to the top-left luma sample postion (xCb, yCb) of the current coding block;
• set the value of the luma intra prediction mode associated with the current coding block to a second default value when the second indication information indicates that an Intra Block Copy, IBC, mode or palette mode is applied for the luma component at the luma position (cbWidth/2, cbHeight/2), relative to the top-left luma sample postion (xCb, yCb) of the current coding block;
• and
• obtain a value of a chroma intra prediction mode based on the value of the luma intra prediction mode of the current coding block.