Encoder, decoder, encoding method, and decoding method
An encoder includes circuitry and memory. Using the memory, the circuitry, in operation, selects an encoding mode from among candidates including a decoder-side motion vector refinement (DMVR) encoding mode and a partition encoding mode. When the DMVR encoding mode is selected, the circuitry: obtains a first motion vector for a first image block; derives a second motion vector from the first motion vector using motion search; and generates a prediction image for the first image block using the second motion vector. When the partition encoding mode is selected, the circuitry: determines a plurality of partitions in a second image block; obtains a third motion vector for each partition; and generates a prediction image for the second image block using the third motion vector, without deriving a fourth motion vector from the third motion vector using motion search.
1. A decoder, comprising:
circuitry; and
memory, wherein
using the memory, the circuitry, in operation, determines to perform a decoding mode from among candidates including a decoder-side motion vector refinement (DMVR) decoding mode and a partition decoding mode,
when the DMVR decoding mode is determined to be performed, the circuitry:
obtains a first motion vector for a first image block;
derives a second motion vector from the first motion vector using motion search; and
generates a prediction image for the first image block using the second motion vector; and
when the partition decoding mode is determined to be performed, the circuitry:
determines a plurality of partitions in a second image block;
obtains a third motion vector for each partition; and
generates a prediction image for the second image block using the third motion vector, without deriving a fourth motion vector from the third motion vector using motion search.
2. An encoding method, comprising:
selecting an encoding mode from among candidates including a decoder-side motion vector refinement (DMVR) encoding mode and a partition encoding mode,
when the DMVR encoding mode is selected:
obtaining a first motion vector for a first image block;
deriving a second motion vector from the first motion vector using motion search; and
generating a prediction image for the first image block using the second motion vector; and
when the partition encoding mode is selected:
determining a plurality of partitions in a second image block;
obtaining a third motion vector for each partition;
generating a prediction image for the second image block using the third motion vector, without deriving a fourth motion vector from the third motion vector using motion search; and
storing, into a bitstream, a flag indicating the partition encoding mode.