Image decoding method, and device for same

1. An image decoding method performed by a decoding apparatus, the method comprising:

obtaining image information from a bitstream; and

decoding a current picture based on the image information,

wherein the obtaining the image information includes:

obtaining a flag for whether a Picture Header (PH) Network Abstraction Layer (NAL) unit for the current picture is present; and

obtaining a PH for the current picture based on the flag,

wherein a NAL unit including the PH is derived based on the flag, and

wherein based on the flag representing that the PH NAL unit is not present, the current picture includes only one slice.

2. The method of claim 1 , wherein when the flag represents that the PH NAL unit is present, the PH is included in the PH NAL unit, and

when the flag represents that the PH NAL unit is not present, the PH is included in a Video Coding Layer (VCL) NAL unit for the slice in the current picture.

3. The method of claim 2 , wherein the VCL NAL unit for the slice include a slice header and slice data for the slice.

4. The method of claim 2 , wherein when the flag represents that the PH NAL unit is not present, PH NAL units are not present for all pictures in a Coded Video Layer Sequence (CLVS) including the current picture.

5. The method of claim 4 , wherein when the flag represents that the PH NAL unit is not present, picture headers for all the pictures in the CLVS are included in VCL NAL units including slice headers of all the pictures.

6. The method of claim 1 , wherein the flag is obtained in a slice header.

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

generating a Picture Header (PH) for a current picture; and

encoding image information including the PH,

wherein the encoding the image information includes:

determining whether a Picture Header (PH) Network Abstraction Layer (NAL) unit for the current picture is present;

deriving a NAL unit including the PH based on a result of the determination; and

encoding the NAL unit and a flag for whether the PH NAL unit is present,

wherein based on the flag representing that the PH NAL unit is not present, the current picture includes only one slice.

8. The method of claim 7 , wherein when the PH NAL unit is present, the PH is included in the PH NAL unit, and

when the PH NAL unit is not present, the PH is included in a Video Coding Layer (VCL) NAL unit for the slice in the current picture.

9. The method of claim 8 , wherein the VCL NAL unit for the slice include a slice header and slice data for the slice.

10. The method of claim 7 , wherein when the PH NAL unit is not present, PH NAL units are not present for all pictures in a Coded Video Layer Sequence (CLVS) including the current picture.

11. The method of claim 10 , wherein when the PH NAL unit is not present, picture headers for all the pictures in the CLVS are included in VCL NAL units including slice headers of all the pictures.

12. The method of claim 7 , wherein the flag is signaled in a slice header.

13. A non-transitory computer-readable storage medium storing a bitstream generated by a method, the method comprising:

generating a Picture Header (PH) for a current picture;

encoding image information including the PH; and

generating the bitstream including the image information,

wherein the encoding the image information includes:

determining whether a Picture Header (PH) Network Abstraction Layer (NAL) unit for the current picture is present;

deriving a NAL unit including the PH based on a result of the determination; and

encoding the NAL unit and a flag for whether the PH NAL unit is present,

wherein based on the flag representing that the PH NAL unit is not present, the current picture includes only one slice.

14. The computer-readable storage medium of claim 13 , wherein when the PH NAL unit is present, the PH is included in the PH NAL unit, and

when the PH NAL unit is not present, the PH is included in a Video Coding Layer (VCL) NAL unit for the slice in the current picture.