Image encoding/decoding method and device for determining sub-layers on basis of required number of sub-layers, and bit-stream transmission method

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

determining at least one layer in an output layer set (OLS); and

determining a number of sublayers for the at least one layer,

wherein a number of sublayers for a current layer in the OLS is determined based on a minimum value between a first value and a second value,

wherein the first value is determined based on a number of sublayers for a first layer, and

wherein the second value is determined based on a maximum temporal identifier among temporal identifiers designated for at least one picture, of the current layer, to be referenced by the first layer.

2. The image decoding method of claim 1 ,

wherein the number of sublayers for the current layer is determined based on an OLS mode, and

wherein the OLS mode is determined based on OLS mode index information obtained from a bitstream.

3. The image decoding method of claim 1 ,

wherein a layer index of the first layer is greater than a layer index of the current layer, and

wherein a network abstraction layer (NAL) unit identifier of the first layer is greater than a NAL unit identifier of the current layer.

4. The image decoding method of claim 1 , further comprising obtaining a sub-bitstream from a bitstream based on the number of sublayers for the current layer.

5. The image decoding method of claim 4 ,

wherein the sub-bitstream is obtained by removing a predetermined network abstraction layer (NAL) unit from the bitstream, and

wherein the predetermined NAL unit is determined based on comparison between a temporal identifier of the predetermined NAL unit and a number of sublayers determined for a second layer corresponding to the predetermined NAL unit.

6. The image decoding method of claim 5 ,

wherein the predetermined NAL unit is determined based on whether a value of the temporal identifier of the predetermined NAL unit is equal to or greater than a value corresponding to the number of sublayers determined for the second layer corresponding to the predetermined NAL unit among layers of a predetermined OLS, and

wherein the OLS is identified based on information signaled by a video parameter set (VPS).

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

determining at least one layer in an output layer set (OLS); and

determining a number of sublayers for the at least one layer,

wherein a number of sublayers for a current layer in the OLS is determined based on a minimum value between a first value and a second value,

wherein the first value is determined based on a number of sublayers for a first layer, and

wherein the second value is determined based on a maximum temporal identifier among temporal identifiers designated for at least one picture, of the current layer, to be referenced by the first layer.

8. A non-transitory computer-readable recording medium storing a bitstream generated by the image encoding method of claim 7 .

9. A method for transmitting a bitstream generated by an image encoding method, the image encoding method comprising:

determining at least one layer in an output layer set (OLS); and

determining a number of sublayers for the at least one layer,

wherein a number of sublayers for a current layer in the OLS is determined based on a minimum value between a first value and a second value,

wherein the first value is determined based on a number of sublayers for a first layer, and

wherein the second value is determined based on a maximum temporal identifier among temporal identifiers designated for at least one picture, of the current layer, to be referenced by the first layer.