An image decoding method includes reconstructing a current image by performing deblocking filtering on a boundary of at least one reconstruction block from among reconstruction blocks, wherein the reconstructing of the current image by performing the deblocking filtering on the boundary of the at least one reconstruction block from among the reconstruction blocks includes, when a prediction mode of at least one reconstruction mode from among blocks located on both sides of the boundary of the at least one reconstruction block is a combined inter-intra prediction mode, determining that a value of a boundary filtering strength applied to the boundary of the at least one reconstruction block is a predetermined value and performing deblocking filtering on the boundary of the at least one reconstruction block based on the determined value of the boundary filtering strength.