Methods for intra prediction, encoder and decoder

A method for intra prediction, applied to a decoder, the method comprising:

• obtaining multiple previously reconstructed neighbouring blocks corresponding to a current processing block;
• obtaining multiple first prediction modes according to prediction modes of neighbouring blocks of the multiple previously reconstructed neighbouring blocks;
• if the multiple first prediction modes comprise at least two directional modes, taking directional modes comprised in the multiple first prediction modes as first prediction directions, wherein the first prediction directions comprise a luma intra prediction direction;
• performing, according to a preset operation rule, operation on multiple first prediction directions of the first prediction directions to obtain second prediction directions;
• obtaining a prediction mode set according to the second prediction directions and the multiple first prediction modes;
• and
• performing intra prediction on the current processing block based on the prediction mode set.

An encoder comprising a memory and a processor, the memory storing instructions executable on the processor, wherein the processor, when executing the instructions, perform operations of:

• obtaining multiple previously reconstructed neighbouring blocks corresponding to a current processing block;
• determining prediction modes, that are signalled in a bitstream, corresponding to neighbouring blocks of the multiple previously reconstructed neighbouring blocks, to obtain multiple first prediction modes;
• if the multiple first prediction modes comprise at least two directional modes, taking directional modes comprised in the multiple first prediction modes as first prediction directions, wherein the first prediction directions comprise a luma intra prediction direction;
• performing, according to a preset operation rule, operation on multiple first prediction directions of the first prediction directions to obtain second prediction directions;
• obtaining a prediction mode set according to the second prediction directions and the multiple first prediction modes;
• and
• performing intra prediction on the current processing block based on the prediction mode set.

A decoder comprising a memory and a processor, the memory storing instructions executable on the processor, wherein the processor, when executing the instructions, perform operations of:

• obtaining multiple previously reconstructed neighbouring blocks corresponding to a current processing block;
• obtaining multiple first prediction modes according to prediction modes of neighbouring blocks of the multiple previously reconstructed neighbouring blocks;
• if the multiple first prediction modes comprise at least two directional modes, taking directional modes comprised in the multiple first prediction modes as first prediction directions, wherein the first prediction directions comprise a luma intra prediction direction;
• performing, according to a preset operation rule, operation on multiple first prediction directions of the first prediction directions to obtain second prediction directions;
• obtaining a prediction mode set according to the second prediction directions and the multiple first prediction modes;
• and
• performing intra prediction on the current processing block based on the prediction mode set.