Mixed NAL unit type-based image encoding/decoding method and device, and method for transmitting bitstream

An image encoding method performed by an image encoding apparatus, the image encoding method comprising:

• partitioning a current picture into one or more subpictures;
• determining a network abstraction layer (NAL) unit type of each of a plurality of slices included in the one or more subpictures;
• and
• encoding the plurality of slices based on the determined NAL unit type,
• wherein the current picture is partitioned into two or more subpictures based on at least some of the plurality of slices having different NAL unit types, and
• wherein each of the two or more subpictures is treated as one picture based on at least some of the plurality of slices having different NAL unit types,
• wherein all slices in each subpicture included in the current picture have the same NAL unit type.

A method of transmitting a bitstream, the method comprising:

• obtaining the bitstream generated by an image encoding method;
• and
• transmitting the bitstream,
• wherein the image encoding method comprising:
• partitioning a current picture into one or more subpictures;
• determining a network abstraction layer (NAL) unit type of each of a plurality of slices included in the one or more subpictures;
• and
• encoding the plurality of slices based on the determined NAL unit type,
• wherein the current picture is partitioned into two or more subpictures based on at least some of the plurality of slices having different NAL unit types, and
• wherein each of the two or more subpictures is treated as one picture based on at least some of the plurality of slices having different NAL unit types,
• wherein all slices in each subpicture included in the current picture have the same NAL unit type.