Method and device for encoding/decoding image using geometrically modified picture

1. A method for encoding an image, the method comprising:

generating geometric modification information of a current picture;

determining a geometric modification flag indicating whether or not geometric modification is used for intra prediction of the current picture;

determining reference geometric modification index indicating reference geometric modification information among one or more previously used geometric modification information;

determining predicted geometric modification information of the current picture based on the reference geometric modification information of the current picture;

determining residual geometric modification information indicating a difference between the predicted geometric modification information of the current picture and the geometric modification information of the current picture;

generating a geometrically modified picture of the current picture by modifying a reference picture of the current picture based on the geometric modification information of the current picture;

generating a prediction block of a current block by performing intra prediction based on samples in the current picture and samples in the geometrically modified picture; and

encoding a bitstream comprising the geometric modification flag, the reference geometric modification index, the residual geometric modification information,

wherein,

the geometrically modified picture is used for the intra prediction of the current block when the samples in the current picture on a prediction direction for the intra prediction are not available,

when the prediction direction for the intra prediction is left, top or top-left, the samples in the current picture are used for the intra prediction of the current block,

when the prediction direction for the intra prediction is right, bottom or bottom-right, the samples in the geometrically modified picture are used for the intra prediction of the current block, and

when the prediction direction for the intra prediction is top-right, or bottom-left, both of the saamples in the current picture and the samples in the geometrically modified picture are used for the intra prediction of the current block.

2. The method of claim 1 , wherein the geometric modification information is reconfigured by simplifying or predicting the geometric modification information.

3. The method of claim 1 , wherein the geometric modification information is generated based on a change in pixel information between a current picture including the current block and the reference picture.

4. The method of claim 3 , wherein the geometric modification information is generated based on matching information between feature points that are extracted from each of the current picture and the reference picture.

5. The method of claim 1 , wherein the generating the geometric modified picture comprises

identifying one point within the reference picture, the point corresponding to one point within the geometric modified picture; and

setting pixel information of the corresponding point within the reference picture to pixel information of the point within the geometric modified picture.

6. The method of claim 5 , wherein when the point corresponding to the point within the geometric modified picture is not present within the reference picture, a point closest to the corresponding point within the reference picture is identified as the corresponding point.

7. A method for decoding an image, the method comprising:

obtaining, from a bitstream, a geometric modification flag of a current picture, the geometric modification flag indicating whether or not geometric modification is used for intra prediction in the current picture;

obtaining, from the bitstream, reference geometric modification index indicating reference geometric modification information among one or more previously used geometric modification information;

obtaining, from the bitstream, residual geometric modification information indicating a difference between the reference geometric modification information of the current picture and geometric modification information of the current picture;

when the geometric modification flag indicates that geometric modification is used for intra prediction in the current picture, determining the reference geometric modification information of the current picture from the previously used geometric modification information based on the reference geometric modification index;

determining predicted geometric modification information of the current picture based on the reference geometric modification information of the current picture;

determining the geometric modification information of the current picture based on the predicted geometric modification information of the current picture and the residual geometric modification information of the current picture; and

generating a geometrically modified picture of the current picture by modifying a reference picture of the current picture based on the geometric modification information of the current picture; and

generating a prediction block of a current block by performing intra prediction based on samples in the current picture and samples in the geometrically modified picture,

wherein

the geometrically modified picture is used for the intra prediction of the current block when the samples in the current picture on a prediction direction for the intra prediction are not available,

when the prediction direction for the intra prediction is left, top or top-left, the samples in the current picture are used for the infra prediction of the current block,

when the prediction direction for the intra prediction is right, bottom or bottom-right, the samples in the geometrically modified picture are used for the intra prediction of the current block, and

when the prediction direction for the intra prediction is top-right, or bottom-left, both of the samples in the current picture and the samples in the geometrically modified picture are used for the intra prediction of the current block.

8. The method of claim 7 , wherein the generating the geometric modified picture comprises:

identifying one point within the reference picture, the point corresponding to one point within the geometric modified picture; and

setting pixel information of the corresponding point within the reference picture to pixel information of the point within the geometric modified picture.

9. The method of claim 8 , wherein when the point corresponding to the point within the geometric modified picture is not present within the reference picture, a point closest to the corresponding point within the reference picture is identified as the corresponding point.

10. The method of claim 8 , wherein when the corresponding point within the reference picture has a real number coordinate, one or more points each having an integer number coordinate and neighboring to the corresponding point within the reference picture is identified, and pixel information of the corresponding point within the reference picture is derived based on pixel information of the one or more points each having the integer number coordinate.

11. The method of claim 7 , wherein the generating the geometric modified picture is performed in at least one unit of a picture, a tile, a coding unit, and a prediction unit.

12. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, configure the processor to:

obtain, from a bitstream, a geometric modification flag of a current picture, the geometric modification flag indicating whether or not geometric modification is used for intra prediction in the current picture;

obtain, from the bitstream, reference geometric modification index indicating reference geometric modification information among one or more previously used geometric modification information;

obtain, from the bitstream, residual geometric modification information indicating a difference between the reference geometric modification information of the current picture and geometric modification information of the current picture;

when the geometric modification flag indicates that geometric modification is used for intra prediction in the current picture, determine the reference geometric modification information of the current picture from the previously used geometric modification information based on the reference geometric modification index;

determine predicted geometric modification information of the current picture based on the reference geometric modification information of the current picture;

determine the geometric modification information of the current picture based on the predicted geometric modification information of the current picture and the residual geometric modification information of the current picture;

generate a geometrically modified picture of the current picture by modifying a reference picture of the current picture based on the geometric modification information of the current picture; and

generate a prediction block of a current block by performing intra prediction based on samples in the current picture and samples in the geometrically modified picture,

wherein,

the geometrically modified picture is used for the intra prediction of the current block when the samples in the current picture on a prediction direction for the intra prediction are not available,

when the prediction direction for the intra prediction is left, top or top-left, the samples in the current picture are used for the intra prediction of the current block,

when the prediction direction for the intra prediction is right, bottom or bottom-right, the samples in the geometrically modified picture are used for the intra prediction of the current block, and

when the prediction direction for the intra prediction is top-right, or bottom-left, both of the samples in the current picture and the samples in the geometrically modified picture are used for the intra prediction of the current block.