Image decoding method and device using DPB parameter for OLS

An image encoding apparatus comprising:

• a memory;
• and
• at least one processor connected to the memory, the at least one processor configured to:
• generate Decoded Picture Buffer (DPB) parameter syntax structures including DPB parameter syntax structure of a target Output Layer Set (OLS);
• perform a picture management process for pictures of a DPB based on the DPB parameter syntax structure of the target OLS;
• construct a reference picture list for a current picture based on the pictures of the DPB;
• perform inter prediction for a block in the current picture based on the reference picture list;
• generate an OLS DPB parameter index for the DPB parameter syntax structure of the target OLS;
• and
• encode image information including the OLS DPB parameter index, the DPB parameter syntax structures and prediction information for the block,
• wherein the OLS DPB parameter index specifies the DPB parameter syntax structure for the target OLS among the DPB parameter syntax structures,
• wherein an OLS DPB parameter flag for whether the DPB parameter syntax structure for the target OLS is present in a Video Parameter Set (VPS) syntax is encoded,
• wherein the OLS DPB parameter syntax structure is signaled in the VPS syntax based on a value of the OLS DPB parameter flag.

An apparatus for transmitting data for an image, the apparatus comprising:

• at least one processor configured to obtain a bitstream of image information including Decoded Picture Buffer (DPB) parameter syntax structures and an Output Layer Set (OLS) DPB parameter index for a target OLS;
• and
• a transmitter configured to transmit the data including the bitstream of the image information including the DPB parameter syntax structures and the OLS DPB parameter index,
• wherein DPB parameter syntax structure for the target OLS is derived based on the OLS DPB parameter index, and a picture management process for pictures of a DPB is performed based on the DPB parameter syntax structure for the target OLS,
• wherein the OLS DPB parameter index specifies the DPB parameter syntax structure for the target OLS among the DPB parameter syntax structures,
• wherein an OLS DPB parameter flag for whether the DPB parameter syntax structure for the target OLS is present in a Video Parameter Set (VPS) syntax is obtained,
• wherein the OLS DPB parameter syntax structure is obtained in the VPS syntax based on a value of the OLS DPB parameter flag.