Encoder, decoder, encoding method, decoding method, and recording medium

An encoding method, comprising:

• partitioning a picture into a plurality of blocks, using a set of block partition modes obtained by combining one or more block partition modes each of which defines a partition type, the picture being read from a memory;
• and
• encoding the plurality of blocks, wherein
• the set of block partition modes includes a first block partition mode that defines a partition direction and a total number of partitions for partitioning a first block, and a second block partition mode that defines a partition direction and a total number of partitions for partitioning a second block which is one of blocks obtained after the first block is partitioned,
• in the partitioning, in a case where the total number of partitions of the first block partition mode is three, the second block is a center block among the blocks obtained after the first block is partitioned, and the partition direction of the second block partition mode is same as the partition direction of the first block partition mode, a parameter for identifying the second block partition mode includes a first flag indicating whether a block is to be partitioned horizontally or vertically, and does not include a second flag indicating a total number of partitions into which the block is to be partitioned.

A decoder that decodes an encoded signal, the decoder comprising:

• circuitry;
• and
• memory, wherein using the memory, the circuitry:
• partitions the encoded signal into a plurality of blocks, using a set of block partition modes obtained by combining one or more block partition modes each of which defines a partition type, the encoded signal being read from the memory;
• and
• decodes the plurality of blocks,
• the set of block partition modes includes a first block partition mode that defines a partition direction and a total number of partitions for partitioning a first block, and a second block partition mode that defines a partition direction and a total number of partitions for partitioning a second block which is one of blocks obtained after the first block is partitioned,
• in case where the total number of partitions of the first block partition mode is three, the second block is a center block among the blocks obtained after the first block is partitioned, and the partition direction of the second block partition mode is same as the partition direction of the first block partition mode, a parameter for identifying the second block partition mode includes a first flag indicating whether a block is to be partitioned horizontally or vertically, and does not include a second flag indicating a total number of partitions into which the block is to be partitioned.

A decoding method, comprising:

• partitioning an encoded signal into a plurality of blocks, using a set of block partition modes obtained by combining one or more block partition modes each of which defines a partition type, the encoded signal being read from a memory;
• and
• decoding the plurality of blocks, wherein
• the set of block partition modes includes a first block partition mode that defines a partition direction and a total number of partitions for partitioning a first block, and a second block partition mode that defines a partition direction and a total number of partitions for partitioning a second block which is one of blocks obtained after the first block is partitioned,
• in the partitioning, in a case where the total number of partitions of the first block partition mode is three, the second block is a center block among the blocks obtained after the first block is partitioned, and the partition direction of the second block partition mode is same as the partition direction of the first block partition mode, a parameter for identifying the second block partition mode includes a first flag indicating whether a block is to be partitioned horizontally or vertically, and does not include a second flag indicating a total number of partitions into which the block is to be partitioned.

A non-transitory computer-readable recording medium storing a bitstream, the bitstream including an encoded signal and syntax information according to which a decoder performs:

• partitioning a picture into a plurality of blocks, using a set of block partition modes obtained by combining one or more block partition modes each of which defines a partition type, the picture being read from a memory;
• and
• decoding the plurality of blocks, wherein
• the set of block partition modes includes a first block partition mode that defines a partition direction and a total number of partitions for partitioning a first block, and a second block partition mode that defines a partition direction and a total number of partitions for partitioning a second block which is one of blocks obtained after the first block is partitioned,
• in the partitioning, in a case where the total number of partitions of the first block partition mode is three, the second block is a center block among the blocks obtained after the first block is partitioned, and the partition direction of the second block partition mode is same as the partition direction of the first block partition mode, a parameter for identifying the second block partition mode includes a first flag indicating whether a block is to be partitioned horizontally or vertically, and does not include a second flag indicating a total number of partitions into which the block is to be partitioned.