This application relates to the encoding and decoding field and discloses an image encoding method, an image decoding method, and a related device. The image decoding method includes: obtaining first information based on a first bitstream; performing size transformation on the first information to obtain second information, where the second information includes information about a chrominance component in a first image format; reconstructing a first image based on the second information; obtaining third information based on the second bitstream, where sizes of the third information in spatial dimension and channel dimension are consistent with those of the first information; performing size transformation on the third information to obtain fourth information, where the fourth information includes information about a chrominance component in the second image format; and reconstructing a second image based on the fourth information.