decoding, from a high-level syntax structure of a bitstream, a first syntax element for specifying a reference size of pictures referring to the high-level syntax structure and a second syntax element for specifying a picture size scaled from the reference size of the pictures referring to the high-level syntax structure;

deriving, based on the first syntax element and the second syntax element, at least one offset factor and at least one scale factor representing a scale difference between a current picture including a current block to be decoded and a reference picture referred to by the current block, wherein the at least one scale factor and the at least one offset factor are used to modify a sample position indicated by a motion vector of the current block within the reference picture; and

generating a prediction bock of the current block from the reference picture, by using the motion vector of the current block, the at least one scale factor, and the at least one offset factor,

wherein the at least one scale factor includes a horizontal scale factor and a vertical scale factor that are respectively applied to horizontal and vertical components of the motion vector of the current block, and

wherein the at least one offset factor includes a horizontal offset factor and a vertical offset factor that are respectively applied to horizontal and vertical components of the motion vector of the current block.