Image encoding/decoding method and device, and recording medium storing bit stream

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

decoding first MPM information indicating whether a planar mode in a first MPM list is applied to a current block;

deriving an intra prediction mode of the current block to be the planar mode in response to the first MPM information indicating that the planar mode in the first MPM list is applied to the current block;

decoding second MPM information indicating the intra prediction mode of the current block in a second MPM list in response to the first MPM information indicating that the planar mode in the first MPM list is not applied to the current block, and deriving the intra prediction mode of the current block in the second MPM list based on the second MPM information;

configuring a reference sample for intra prediction of the current block;

obtaining prediction samples of the current block based on the intra prediction mode and the reference sample,

obtaining residual samples of the current block; and

generating reconstructed samples of the current block by adding the prediction samples and the residual samples of the current block,

wherein the second MPM list comprises a first intra prediction mode of a neighboring block of the current block and a second intra prediction mode having an index that is greater than or smaller than an index of the first intra prediction mode, and

wherein an offset between indexes of the first intra prediction mode and the second intra prediction mode is greater than or equal to 2.

2. The method of claim 1 , wherein the deriving the intra prediction mode of the current block comprises:

selecting one MPM list among a plurality of MPM lists in case the intra prediction mode of the current block is determined to be included in the MPM list; and

deriving the intra prediction mode of the current block from the selected MPM list.

3. The method of claim 1 , wherein the first MPM list has fewer MPM candidates than the second MPM list.

4. The method of claim 1 , wherein the MPM list comprises DC mode in case the intra prediction mode of the neighboring block is a non-directional mode.

5. The method of claim 1 , wherein the configuring the reference sample is performed based on a reconstructed sample line selected among a plurality of reconstructed sample lines based on information signaled through a bitstream.

6. The method of claim 5 , wherein the configuring the reference sample is performed based on a first reconstructed sample line among the plurality of reconstructed sample lines in case an upper boundary of the current block is a boundary of a coding tree block (CTB).

7. The method of claim 5 , wherein the configuring the reference sample further comprises filtering the selected reconstructed sample line, and

wherein the filtering is performed only when a first reconstructed sample line is selected.

8. The method of claim 1 , wherein, in case the intra prediction mode of the current block is a DC mode and a width of the current block is not equal to a height of the current block, the prediction samples of the current block are obtained by using an average of reference samples adjacent to longer side among the width and the height of the current block.

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

determining an intra prediction mode of a current block;

configuring a reference sample for intra prediction of the current block;

obtaining prediction samples of the current block based on the intra prediction mode and the reference sample;

obtaining residual samples of the current block by using the prediction samples of the current block;

encoding first MPM information based on the intra prediction mode of the current block, the first MPM information indicating whether a planar mode in a first MPM list is applied to the current block;

encoding second MPM information based on the intra prediction mode of the current block in response to the first MPM information indicating that the planar mode in the first MPM list is not applied to the current block, the second MPM information indicating the intra prediction mode of the current block in a second MPM list; and

encoding the residual samples of the current block,

wherein the second MPM list comprises a first intra prediction mode of a neighboring block of the current block and a second intra prediction mode having an index that is greater than or smaller than an index of the first intra prediction mode, and

wherein an offset between indexes of the first intra prediction mode and the second intra prediction mode is greater than or equal to 2.

10. The method of claim 9 , wherein the determining the intra prediction mode of the current block comprises:

selecting one MPM list to which the intra prediction mode of the current block among a plurality of MPM lists in case the intra prediction mode of the current block is determined to be included in the MPM list; and

determining the intra prediction mode of the current block based on the selected MPM list.

11. The method of claim 9 , wherein the first MPM list has fewer MPM candidates than the second MPM list.

12. The method of claim 9 , wherein the MPM list comprises DC mode in case the intra prediction mode of the neighboring block is a non-directional mode.

13. The method of claim 9 , wherein the configuring the reference sample is performed based on a reconstructed sample line selected among a plurality of reconstructed sample lines, and information on the selection of the reconstructed sample line is encoded into a bitstream.

14. The method of claim 13 , wherein the configuring the reference sample is performed based on a first reconstructed sample line among the plurality of reconstructed sample lines in case an upper boundary of the current block is a boundary of a coding tree block (CTB).

15. The method of claim 13 , wherein the configuring the reference sample further comprises filtering the selected reconstructed sample line, and

the filtering is performed only when a first reconstructed sample line is selected.

16. The method of claim 9 , wherein, in case that the intra prediction mode of the current block is a DC mode and a width of the current block is not equal to a height of the current block, the prediction samples of the current block are obtained by using an average of reference samples adjacent to longer side among the width and the height of the current block.

17. A non-transitory computer-readable recording medium storing a bitstream which is generated by an image encoding method, the image encoding method comprising:

determining an intra prediction mode of a current block;

configuring a reference sample for intra prediction of the current block;

obtaining prediction samples of the current block based on the intra prediction mode and the reference sample;

obtaining residual samples of the current block by using the prediction samples of the current block;

encoding first MPM information based on the intra prediction mode of the current block, the first MPM information indicating whether a planar mode in a first MPM list is applied to the current block;

encoding second MPM information based on the intra prediction mode of the current block in response to the first MPM information indicating that the planar mode in the first MPM list is not applied to the current block, the second MPM information indicating the intra prediction mode of the current block in a second MPM list; and

encoding the residual samples of the current block,

wherein the second MPM list comprises a first intra prediction mode of a neighboring block of the current block and a second intra prediction mode having an index that is greater than or smaller than an index of the first intra prediction mode, and

wherein an offset between indexes of the first intra prediction mode and the second intra prediction mode is greater than or equal to 2.