Image processing method based on inter prediction mode, and device therefor
In the present disclosure, a method of decoding a video signal and a device therefor are disclosed. Specifically, a method of decoding an image based on an inter prediction mode includes deriving a motion vector of an available spatial neighboring block around a current block; deriving a collocated block of the current block based on the motion vector of the spatial neighboring block; deriving a motion vector in a sub-block unit in the current block based on a motion vector of the collocated block; and generating a prediction block of the current block using the motion vector derived in the sub-block unit, wherein the collocated block may be specified by the motion vector of the spatial neighboring block in one pre-defined reference picture.
1. A method of decoding an image, comprising:
obtaining a reference index of a collocated picture being used for a motion vector prediction;
based on that a reference picture of a spatial neighboring block around a current block is the same as one pre-determined reference picture among reference pictures included in a reference picture list, deriving a collocated block of the current block in the one pre-determined reference picture using a motion vector of the spatial neighboring block, wherein the one pre-determined reference picture is based on the reference index of the collocated picture;
deriving motion vectors of sub-blocks in the current block based on the motion vector of the collocated block;
generating prediction samples of the current block based on the motion vectors of the sub-blocks; and
generating reconstructed samples of the current block based on the prediction samples,
wherein the one pre-determined reference picture is loaded in a picture header or a slice header.
2. The method of claim 1 , further comprising:
deriving motion vectors of available spatial neighboring blocks among spatial neighboring blocks around the current block in a pre-determined order.
3. The method of claim 2 , wherein the pre-determined order is a block neighboring a left side of the current block, a block neighboring upper side of the current block, a block neighboring a upper side of the current block, a block neighboring a upper-right corner of the current block, a block neighboring a lower-left corner of the current block, and a block neighboring a upper-left corner of the current block.
4. The method of claim 1 , wherein the spatial neighboring block the motion vector of which is used to derive the collocated block is located at a bottom of a left side of the current block.
5. A method of encoding an image, comprising:
based on that a reference picture of a spatial neighboring block around a current block is the same as one pre-determined reference picture among reference pictures included in a reference picture list, deriving a collocated block of the current block in the one pre-determined reference picture using a motion vector of the spatial neighboring block;
deriving motion vectors of sub-blocks in the current block based on a motion vector of the collocated block;
generating prediction samples of the current block based on the motion vectors of the sub-blocks;
generating residual samples of the current block based on the prediction samples; and
generating a reference index indicating the one pre-determined reference picture,
wherein the one pre-determined reference picture is defined in a picture header or a slice header.
6. The method of claim 5 , further comprising:
deriving motion vectors of available spatial neighboring blocks among spatial neighboring blocks around the current block in a pre-determined order.
7. The method of claim 5 , wherein the pre-determined order is a block neighboring a left side of the current block, a block neighboring upper side of the current block, a block neighboring a upper side of the current block, a block neighboring a upper-right corner of the current block, a block neighboring a lower-left corner of the current block, and a block neighboring a upper-left corner of the current block.
8. The method of claim 5 , wherein the spatial neighboring block the motion vector of which is used to derive the collocated block is located at a bottom of a left side of the current block.
9. 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:
based on that a reference picture of a spatial neighboring block around a current block is the same as one pre-determined reference picture among reference pictures included in a reference picture list, deriving a collocated block of the current block in the one pre-determined reference picture using a motion vector of the spatial neighboring block;
deriving motion vectors of sub-blocks in the current block based on a motion vector of the collocated block;
generating prediction samples of the current block based on the motion vectors of the sub-blocks;
generating residual samples of the current block based on the prediction samples; and
generating a reference index indicating the one pre-determined reference picture, wherein the one pre-determined reference picture is defined in a picture header or a slice header.