Disclosed is a method for obtaining information on sub-units partitioned from a picture. The method comprises: decoding, from a bitstream, CTU size information indicating the size of coding tree units (CTUs) within the picture; decoding, from the bitstream, sub-picture partition information expressing sub-pictures within the picture in units of the CTU sizes; decoding, from the bitstream, partition information related to partition of the picture into one or more tiles; and decoding, from the bitstream, partition information related to partition of the picture into one or more slices.