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

1 . An encoder comprising:

circuitry; and

memory coupled to the circuitry,

wherein, in operation, the circuitry:

when a value of a parameter indicating whether a multilayer coding scheme is used to encode one or more pictures is greater than 0, encodes a first flag indicating whether use of one or more interlayer reference pictures for interlayer prediction is allowed; and

switches between a first scheme and a second scheme, the first scheme being for setting the first flag to 0 and encoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to encode the one or more pictures is 0, the second scheme being for not encoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to encode the one or more pictures is 0.

2 . The encoder according to claim 1 ,

wherein the use of the one or more interlayer reference pictures is allowed when (i) the first flag is encoded and (ii) the first flag indicates that the use of the one or more interlayer reference pictures is allowed,

the use of the one or more interlayer reference pictures is not allowed when (i) the first flag is encoded and (ii) the first flag indicates that the use of the one or more interlayer reference pictures is not allowed, and

the use of the one or more interlayer reference pictures is not allowed when the first flag is not encoded.

3 . The encoder according to claim 1 ,

wherein the circuitry encodes a second flag which indicates whether any of the one or more interlayer reference pictures is used as a reference picture that is included in a reference picture list, when the use of the one or more interlayer reference pictures is allowed.

4 . The encoder according to claim 3 ,

wherein a reference picture different from any of the one or more interlayer reference pictures is used as the reference picture that is included in the reference picture list, when (I-i) the second flag is encoded and (I-ii) the second flag indicates that any of the one or more interlayer reference pictures is not used as the reference picture that is included in the reference picture list, or (II) the second flag is not to be encoded.

5 . The encoder according to claim 1 ,

wherein the parameter is a video parameter set ID,

the video parameter set ID is 0 or greater,

when the video parameter set ID is 0, the multilayer coding scheme is not used to encode the one or more pictures, and

when the video parameter set ID is greater than 0, the multilayer coding scheme is used to encode the one or more pictures, and the video parameter set ID indicates an identifier of a video parameter set for encoding the one or more pictures using the multilayer coding scheme.

6 . A decoder comprising:

circuitry; and

memory coupled to the circuitry,

wherein, in operation, the circuitry:

when a value of a parameter indicating whether a multilayer coding scheme is used to decode one or more pictures is greater than 0, decodes a first flag indicating whether use of one or more interlayer reference pictures for interlayer prediction is allowed; and

switches between a first scheme and a second scheme, the first scheme being for setting the first flag to 0 and decoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to decode the one or more pictures is 0, the second scheme being for not decoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to decode the one or more pictures is 0.

7 . The decoder according to claim 6 ,

wherein the use of the one or more interlayer reference pictures is allowed when (i) the first flag is decoded and (ii) the first flag indicates that the use of the one or more interlayer reference pictures is allowed,

the use of the one or more interlayer reference pictures is not allowed when (i) the first flag is decoded and (ii) the first flag indicates that the use of the one or more interlayer reference pictures is not allowed, and

the use of the one or more interlayer reference pictures is not allowed when the first flag is not decoded.

8 . The decoder according to claim 6 ,

wherein the circuitry decodes a second flag which indicates whether any of the one or more interlayer reference pictures is used as a reference picture that is included in a reference picture list, when the use of the one or more interlayer reference pictures is allowed.

9 . The decoder according to claim 8 ,

wherein a reference picture different from any of the one or more interlayer reference pictures is used as the reference picture that is included in the reference picture list, when (I-i) the second flag is decoded and (I-ii) the second flag indicates that any of the one or more interlayer reference pictures is not used as the reference picture that is included in the reference picture list, or (II) the second flag is not to be decoded.

10 . The decoder according to claim 6 ,

wherein the parameter is a video parameter set ID,

the video parameter set ID is 0 or greater,

when the video parameter set ID is 0, the multilayer coding scheme is not used to decode the one or more pictures, and

when the video parameter set ID is greater than 0, the multilayer coding scheme is used to decode the one or more pictures, and the video parameter set ID indicates an identifier of a video parameter set for decoding the one or more pictures using the multilayer coding scheme.

11 . An encoding method which is performed by an encoder, the encoding method comprising:

when a value of a parameter indicating whether a multilayer coding scheme is used to encode one or more pictures is greater than 0, encoding a first flag indicating whether use of one or more interlayer reference pictures for interlayer prediction is allowed; and

switching between a first scheme and a second scheme, the first scheme being for setting the first flag to 0 and encoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to encode the one or more pictures is 0, the second scheme being for not encoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to encode the one or more pictures is 0.

12 . A decoding method which is performed by a decoder, the decoding method comprising:

when a value of a parameter indicating whether a multilayer coding scheme is used to decode one or more pictures is greater than 0, decoding a first flag indicating whether use of one or more interlayer reference pictures for interlayer prediction is allowed; and

switching between a first scheme and a second scheme, the first scheme being for setting the first flag to 0 and decoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to decode the one or more pictures is 0, the second scheme being for not decoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to decode the one or more pictures is 0.

13 . A non-transitory computer readable medium storing a bitstream,

the bitstream comprising a plurality of parameters for a decoder to perform a decoding process; and

in the decoding process,

when a value of a parameter indicating whether a multilayer coding scheme is used to decode one or more pictures is greater than 0, a first flag indicating whether use of one or more interlayer reference pictures for interlayer prediction is allowed is decoded, and

switching between a first scheme and a second scheme is performed, the first scheme being for setting the first flag to 0 and decoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to decode the one or more pictures is 0, the second scheme being for not decoding the first flag when the value of the parameter indicating whether the multilayer coding scheme is used to decode the one or more pictures is 0.