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. An encoder, comprising:
circuitry; and
memory, wherein
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 image block from a first coding tree unit (CTU);
obtains a first motion vector for the 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 encoding mode is selected, the circuitry:
obtains a second image block from a second coding tree unit (CTU);
determines a plurality of non-rectangular partitions in the second image block;
obtains a third motion vector for each non-rectangular partition;
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; and
stores, into a bitstream, a flag indicating the partition encoding mode.
2. A decoder, comprising:
circuitry; and
memory, wherein
using the memory, the circuitry, in operation, determines to perform a decoding mode based on decoding-mode information from among candidates including a decoder-side motion vector refinement (DMVR) decoding mode and a partition decoding mode, the decoding-mode information including a flag relating to a non-rectangular shape,
when the DMVR decoding mode is determined to be performed, the circuitry:
obtains a first image block from a first coding tree unit (CTU);
obtains a first motion vector for the 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:
obtains a second image block from a second coding tree unit (CTU);
determines a plurality of non-rectangular partitions in the second image block;
obtains a third motion vector for each non-rectangular 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.
3. A non-transitory computer readable medium storing a bitstream,
the bitstream including information, an image block obtained from a coding tree unit (CTU), and a plurality of motion vectors, the information indicating a selected encoding mode which is selected from among candidates including a decoder-side motion vector refinement (DMVR) encoding mode and a partition encoding mode, the information including a flag indicating whether the partition encoding is performed on a non-rectangular shape, wherein
when the information indicates that the DMVR encoding mode is selected,
a first motion vector is obtained from the plurality of motion vectors;
a second motion vector is derived from the first motion vector using motion search; and
a prediction image for the image block is generated using the second motion vector; and
when the information indicates that the partition encoding is selected,
a plurality of non-rectangular partitions are determined in the image block;
a third motion vector is obtained from the plurality of motion vectors for each of the plurality of non-rectangular partitions; and
a prediction image for the image block is generated using the third motion vector, without deriving a fourth motion vector from the third motion vector using motion search.