Image encoding method and apparatus, and image decoding method and apparatus

An image decoding apparatus comprising:

• at least processor configured to split an upper block included in an image based on information about at least one of a split type and a split direction of the upper block to determine at least one lower block from the upper block, if a size of a lower block among the at least one lower block is equal to a predetermined size, to set an intra prediction mode as a prediction mode of the lower block without obtaining information indicating the prediction mode of the lower block from a bitstream, to perform an intra prediction on the lower block among the at least one lower block on the basis of the intra prediction mode set as the prediction mode of the lower block, and to reconstruct the lower block among the at least one lower block,
• wherein:
• the split type represents one of binary-split, tri-split, and quad-split, and
• the split direction represents one of a vertical direction and a horizontal direction.

An image encoding method comprising:

• splitting an upper block included in an image based on at least one of a split type and a split direction of the upper block to determine at least one lower block from the upper block;
• if a size of a lower block among the at least one lower block is equal to a predetermined size, setting an intra prediction mode as a prediction mode of the lower block without generating information indicating the prediction mode of the lower block to be included in a bitstream;
• performing an intra prediction on the lower block among the at least one lower block on the basis of the intra prediction mode set as the prediction mode of the lower block;
• and
• encoding the lower block among the at least one lower block on the basis of a prediction block of the lower block among the at least one lower block,
• wherein:
• the split type represents one of binary-split, tri-split, and quad-split, and
• the split direction represents one of a vertical direction and a horizontal direction.