Inter prediction mode-based image processing method and apparatus therefor
Disclosed are an inter prediction mode-based image processing method and an apparatus therefor. Particularly, a method for processing an image on the basis of inter prediction may comprise the steps of: determining whether a motion vector scale adaptation is applied to a block; up-scaling a down-scaled MVD (Motion Vector Difference) when the motion vector scale adaptation is applied to the block; deriving a MV (Motion Vector) for the block, using the up-scaled MVD and a MVP (Motion Vector Predictor); and generating a predictive block of the block, using the derived MV.
1. A method of decoding a video signal, the method comprising:
obtaining residual samples of a current block;
deriving a motion vector predictor (MVP) based on motion information of a neighbor block of the current block;
obtaining a motion vector difference (MVD) of the current block;
obtaining a flag related to a resolution of the MVD,
determining whether motion vector scale adaptation for the current block is applied based on the flag, wherein a value 0 of the flag specifies that the resolution of the MVD is set to ¼ pel-scale;
rounding the MVP based on the flag;
modifying the MVD to set the resolution of the MVD to the ¼ pel-scale based on the flag;
obtaining a motion vector (MV) of the current block based on the modified MVD and the rounded MVP;
generating prediction samples of the current block based on the MV; and
generating reconstructed samples of the current block based on the prediction samples and the residual samples.
2. The method of claim 1 , wherein the MVD is obtained based on a plurality of syntax elements, comprising:
a first flag including information about whether an absolute value of the MVD is greater than 0;
a second flag including information about an absolute value of the MVD is greater than 1, the second flag being parsed when the MVD is greater than 0;
a value obtained by subtracting 2 from an absolute value of the MVD; and
a third flag including information about a sign of the MVD.
3. The method of claim 2 , wherein the second flag and the third flag are parsed when the MVD is greater than 0, and the value is parsed when the second flag is not equal to 0.
4. The method of claim 1 , wherein the modifying of the MVD up-scales the MVD.
5. The method of claim 1 , wherein the flag is parsed when the obtained MVD is not 0.
6. The method of claim 1 , wherein a round function is applied to the MVP and the MVD is multiplied by 4 based on that the flag is equal to a first value.
7. The method of claim 1 , wherein the MVD is grouped in units of intervals and binary-encoded.
8. The method of claim 7 , wherein the MVD is encoded as a start value of an interval to which the MVD belongs and indication information for indicating the MVD within the interval.
9. The method of claim 8 , wherein the start value is down-scaled at a ratio of a size of the interval and transmitted.
10. The method of claim 9 , wherein the size of the interval is predetermined or transmitted from an encoder.
11. The method of claim 7 , wherein the MVD is grouped in units of intervals and encoded only when the MVD is 2 or more.
12. The method of claim 7 wherein a size of the interval is set to a square number of 2.
13. A method of encoding a video signal, the method comprising:
obtaining a motion vector difference (MVD) of a current block;
rounding a motion vector predictor (MVP) derived from a neighbor block of the current block;
modifying the MVD to set a resolution of the MVD to integer pel-scale;
deriving a motion vector (MV) of the current block based on the modified MVD and the rounded MVP; and
generating a prediction block of the current block based on the derived MV; and
encoding a flag related to the resolution of the MVD,
wherein the flag is related to the rounding and the modifying, and a value 0 of the flag specifies that the resolution of the MVD is set to ¼ pel-scale.
14. A transmission method for data comprising a bitstream for an image, the method comprising:
obtaining the bitstream for the image; and
transmitting the data comprising the bitstream,
wherein the bitstream is generated by performing the steps of:
obtaining a motion vector difference (MVD) of a current block;
rounding a motion vector predictor (MVP) derived from a neighbor block of the current block;
modifying the MVD to set a resolution of the MVD to integer pel-scale;
deriving a motion vector (MV) of the current block based on the modified MVD and the rounded MVP; and
generating a prediction block of the current block based on the derived MV; and
encoding a flag related to the resolution of the MVD,
wherein the flag is related to the rounding and the modifying, and a value 0 of the flag specifies that the resolution of the MVD is set to ¼ pel-scale.