Image encoding/decoding method and apparatus, and recording medium storing bitstream
The present specification discloses a method of decoding an image. The method includes obtaining a motion vector of a collocated block included in a reference picture of a current block in a temporal motion buffer; changing a format of the obtained motion vector; and deriving the motion vector, in which the format is changed, into a temporal motion vector of the current block.
1. A method of decoding an image, the method comprising:
constructing a motion vector candidate list of a current block, the motion vector candidate list comprising a spatial motion vector candidate and a temporal motion vector candidate;
obtaining a motion vector of the current block based on a motion vector candidate selected from the motion vector candidate list; and
obtaining, based on the motion vector of the current block, prediction samples of the current block from a reference picture of the current block,
wherein the spatial motion vector candidate is derived based on a motion vector of a spatial neighboring block of the current block,
wherein the temporal motion vector candidate is derived based on a modified motion vector obtained by modifying a motion vector of a collocated block of the current block,
wherein the modified motion vector is obtained by changing a representation format of the motion vector of the collocated block, and
wherein changing the representation format is performed during a derivation of the temporal motion vector candidate but is not performed during a derivation of the spatial motion vector candidate.
2. The method of claim 1 , wherein a bit-length of the modified motion vector is greater than the motion vector of the collocated block obtained from the temporal motion buffer.
3. The method of claim 1 , wherein changing the representation formation causes the motion vector of a floating point format to be changed to the modified motion vector of a fixed bit-length format.
4. The method of claim 3 , further comprising:
scaling the modified motion vector of the collocated block; and
clipping the scaled modified motion vector within a dynamic range of the fixed bit-length.
5. The method of claim 3 , wherein the motion vector of the floating point format is consisted of 6 bits signed mantissa and 4 bits exponent, and the modified motion vector of the fixed bit-length is represented by 18 bits.
6. A method of encoding an image, the method comprising:
constructing a motion vector candidate list of a current block, the motion vector candidate list comprising a spatial motion vector candidate and a temporal motion vector candidate; and
obtaining a motion vector of the current block based on a motion vector candidate selected from the motion vector candidate list,
wherein, based on the motion vector of the current block, prediction samples of the current block are obtained from a reference picture of the current block,
wherein the spatial motion vector candidate is derived based on a motion vector of a spatial neighboring block of the current block,
wherein the temporal motion vector candidate is derived based on a modified motion vector obtained by modifying a motion vector of a collocated block of the current block,
wherein the modified motion vector is obtained by changing a representation format of the motion vector of the collocated block, and
wherein changing the representation format is performed during a derivation of the temporal motion vector candidate but is not performed during a derivation of the spatial motion vector candidate.
7. A computer-readable non-transitory recording medium including a bitstream encoded by an encoding method comprising:
constructing a motion vector candidate list of a current block, the motion vector candidate list comprising a spatial motion vector candidate and a temporal motion vector candidate; and
obtaining a motion vector of the current block based on a motion vector candidate selected from the motion vector candidate list,
wherein, based on the motion vector of the current block, prediction samples of the current block are obtained from a reference picture of the current block,
wherein the spatial motion vector candidate is derived based on a motion vector of a spatial neighboring block of the current block,
wherein the temporal motion vector candidate is derived based on a modified motion vector obtained by modifying a motion vector of a collocated block of the current block,
wherein the modified motion vector is obtained by changing a representation format of the motion vector of the collocated block, and
wherein changing the representation format is performed during a derivation of the temporal motion vector candidate but is not performed during a derivation of the spatial motion vector candidate.