Encoder, decoder, encoding method, and decoding method
An encoder includes circuitry and memory coupled to the circuitry. The circuitry in operation: determines whether the shape of a current chroma block to be split satisfies a first condition; generates one or more second candidates for a block partitioning method by eliminating one or more predetermined candidates from a plurality of first candidates for a block partitioning method when the current chroma block satisfies the first condition; selects a block partitioning method from among the one or more second candidates; and splits the current chroma block according to the block partitioning method selected.
1. An encoder, comprising:
circuitry; and
memory coupled to the circuitry,
wherein the circuitry, in operation:
determines whether a shape of a current chroma block to be split in an image satisfies a first condition;
generates one or more second candidates for a block partitioning method by eliminating one or more predetermined candidates from a plurality of first candidates for a block partitioning method when the shape of the current chroma block satisfies the first condition;
selects a block partitioning method from among the one or more second candidates; and
splits the current chroma block according to the block partitioning method selected,
the first condition is that the shape of the current chroma block is a vertically elongated block and a width of the current chroma block is equal to a first value,
the first value is one of 16, 8, 4, and 2 pixels, and
the plurality of first candidates include at least a ternary splitting in vertical direction and the one or more second candidates exclude the ternary splitting in vertical direction.
2. A decoder, comprising:
circuitry; and
memory coupled to the circuitry,
wherein the circuitry, in operation:
parses, from an encoded bitstream generated by encoding an image, block partitioning information relating to a block partitioning method according to which a current chroma block to be split in the image is split; and
splits the current chroma block based on the block partitioning information parsed,
when a shape of the current chroma block satisfies a first condition, the block partitioning information is generated by (i) generating one or more second candidates for a block partitioning method by eliminating one or more predetermined candidates from a plurality of first candidates for a block partitioning method and (ii) selecting a block partitioning method from among the one or more second candidates,
the first condition is that the shape of the current chroma block is a vertically elongated block and a width of the current chroma block is equal to a first value,
the first value is one of 16, 8, 4, and 2 pixels, and
the plurality of first candidates include at least a ternary splitting in vertical direction and the one or more second candidates exclude the ternary splitting in vertical direction.