Decoding method, encoding method, decoder, and, encoder

An encoding method of encoding a current block of a video into a bitstream, the encoding method comprising:

• determining two partitions in the current block according to a geometric partitioning mode;
• deriving an angular intra prediction mode from the geometric partitioning mode using a mapping relation between geometric partitioning modes and angular intra prediction modes;
• and
• predicting a first partition among the two partitions according to the angular intra prediction mode, wherein
• in the deriving of the angular intra prediction mode,
• when a shape of the current block is square, a first mapping relation is used as the mapping relation to derive the angular intra prediction mode, and
• when the shape of the current block is not square, a second mapping relation different from the first mapping relation is used as the mapping relation to derive the angular intra prediction mode.

A non-transitory computer readable medium for a computer, storing

• a bitstream that causes the computer to execute a decoding process of decoding a current block, wherein
• the decoding process includes:
• determining two partitions in the current block according to a geometric partitioning mode;
• deriving an angular intra prediction mode from the geometric partitioning mode using a mapping relation between geometric partitioning modes and angular intra prediction modes;
• and
• predicting a first partition among the two partitions according to the angular intra prediction mode, wherein
• in the deriving of the angular intra prediction mode,
• when a shape of the current block is square, a first mapping relation is used as the mapping relation to derive the angular intra prediction mode, and
• when the shape of the current block is not square, a second mapping relation different from the first mapping relation is used as the mapping relation to derive the angular intra prediction mode.

A decoder that decodes a current block of a video from a bitstream, the decoder comprising:

• circuitry;
• and
• memory coupled to the circuitry, wherein
• in operation, the circuitry:
• determines two partitions in the current block according to a geometric partitioning mode;
• derives an angular intra prediction mode from the geometric partitioning mode using a mapping relation between geometric partitioning modes and angular intra prediction modes;
• and
• predicts a first partition among the two partitions according to the angular intra prediction mode, wherein
• in deriving the angular intra prediction mode,
• when a shape of the current block is square, a first mapping relation is used as the mapping relation to derive the angular intra prediction mode, and
• when the shape of the current block is not square, a second mapping relation different from the first mapping relation is used as the mapping relation to derive the angular intra prediction mode.

An encoder that encodes a current block of a video into a bitstream, the encoder comprising:

• circuitry;
• and
• memory coupled to the circuitry, wherein
• in operation, the circuitry:
• determines two partitions in the current block according to a geometric partitioning mode;
• derives an angular intra prediction mode from the geometric partitioning mode using a mapping relation between geometric partitioning modes and angular intra prediction modes;
• and
• predicts a first partition among the two partitions according to the angular intra prediction mode, wherein
• in deriving the angular intra prediction mode,
• when a shape of the current block is square, a first mapping relation is used as the mapping relation to derive the angular intra prediction mode, and
• when the shape of the current block is not square, a second mapping relation different from the first mapping relation is used as the mapping relation to derive the angular intra prediction mode.