Image coding method, image decoding method, image coding apparatus, and image decoding apparatus
An image coding method includes: deriving a candidate for a motion vector predictor from a co-located motion vector; adding the candidate to a list; selecting the motion vector predictor from the list; and coding a current block and coding a current motion vector, wherein the deriving includes: deriving the candidate by a first derivation scheme in the case of determining that each of a current reference picture and a co-located reference picture is a long-term reference picture; and deriving the candidate by a second derivation scheme in the case of determining that each of the current reference picture and the co-located reference picture is a short-term reference picture.
1. An encoding method of encoding each block among blocks of pictures, the encoding method comprising:
deriving a candidate for a motion vector predictor to be used in encoding of a motion vector for a current block to be encoded, from a first motion vector of a first block included in a first picture, the first picture being different from a picture that includes the current block;
adding the derived candidate to a list of candidates;
selecting one motion vector predictor from the list of candidates; and
encoding the current block using a motion vector of the current block and a reference picture of the current block, and encoding the motion vector using the selected motion vector predictor,
wherein the reference picture of the current block is different from the first picture, and
wherein the deriving includes:
determining whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and whether a first reference picture of the first block is a long-term reference picture or a short-term reference picture;
deriving the candidate from the first motion vector without scaling based on a temporal distance in the case of determining that each of the reference picture of the current block and the first reference picture of the first block is a long-term reference picture; and
deriving the candidate from the first motion vector by scaling based on a temporal distance in the case of determining that each of the reference picture of the current block and the first reference picture of the first block is a short-term reference picture.
2. An encoding apparatus that encodes each block among blocks of pictures, the encoding apparatus comprising:
a deriving unit configured to derive a candidate for a motion vector predictor to be used in encoding of a motion vector for a current block to be encoded, from a first motion vector of a first block included in a first picture, the first picture being different from a picture that includes the current block;
an adding unit configured to add the derived candidate to a list of candidates;
a selecting unit configured to select one motion vector predictor from the list of candidates; and
an encoder configured to encode the current block using a motion vector of the current block and a reference picture of the current block, and encode the motion vector using the selected motion vector predictor,
wherein the reference picture of the current block is different from the first picture, and
wherein the deriving unit is configured to:
determine whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and whether a first reference picture of the first block is a long-term reference picture or a short-term reference picture;
derive the candidate from the first motion vector without scaling based on a temporal distance in the case of determining that each of the reference picture of the current block and the first reference picture of the first block is a long-term reference picture; and
derive the candidate from the first motion vector by scaling based on a temporal distance in the case of determining that each of the reference picture of the current block and the first reference picture of the first block is a short-term reference picture.