Provided are methods and apparatuses for encoding and decoding a coding unit of a picture outline. An image decoding method includes obtaining a prediction mode and prediction information of a current block included in a current image, from a bitstream; reconstructing the current block based on at least one of the prediction mode and the prediction information of the current block; when the prediction mode of the current block is a first prediction mode, obtaining a prediction candidate related to a second prediction mode by performing prediction according to the second prediction mode based on the reconstructed current block; and reconstructing an adjacent block reconstructed after the current block by using the prediction candidate related to the second prediction mode.