Moving picture coding method and moving picture decoding method using a determination whether or not a reference block has two reference motion vectors that refer forward in display order with respect to a current picture
A moving picture coding apparatus includes: an inter prediction control unit which determines to code a motion vector using, among candidate predicted motion vectors, a candidate predicted motion vector having the least error with relative to a motion vector derived by motion estimation; a picture type determination unit which generates picture type information; a temporal direction vector calculation unit which derives a candidate predicted motion vector in temporal direct; and a co-located reference direction determination unit which generates, for each picture, a co-located reference direction flag.
1. A moving picture decoding method of decoding a current block to be decoded which is included in a current picture to be decoded, said moving picture decoding method comprising:
determining a display order between the current picture and each of a plurality of reference pictures included in at least one of a first reference picture list and a second reference picture list, the display order being determined using an index of each of the reference pictures;
determining whether or not a reference block has two reference motion vectors that refer forward in the display order with respect to the current picture, the reference block being included in one of the reference pictures, the one of the reference pictures being located forward in the display order with respect to the current picture;
calculating, when the reference block has the two reference motion vectors that refer forward in the display order with respect to the current picture, (i) a first candidate motion vector of the current block by scaling one of the two reference motion vectors and (ii) a second candidate motion vector of the current block by scaling the other one of the two reference motion vectors;
generating a candidate motion vector list in which candidate motion vectors, including the first candidate motion vector and the second candidate motion vector, respectively correspond to values of a candidate motion vector index in one-to-one relationship;
decoding index information for identifying a candidate motion vector to be used in decoding;
decoding difference information about a difference between a current motion vector of the current block included in the current picture and the candidate motion vector to be used in decoding;
calculating the current motion vector by adding the difference information and, from among the candidate motion vectors included in the candidate motion vector list, the candidate motion vector to be used in the decoding, which is identified by the candidate motion vector index having a same value as a value indicated by the index information; and
decoding the current block using the current motion vector.
2. The moving picture decoding method according to claim 1 ,
wherein when an order of assigning an index to a picture which can be referred to by the reference picture is same for the first reference picture list and the second reference picture list, said determining determines whether the reference block has the two reference motion vectors that refer forward in the display order with respect to the current picture.
3. The moving picture decoding method according to claim 1 ,
wherein in said calculating, when the reference block does not have the two reference motion vectors, a candidate motion vector of the current block is calculated by scaling, from among reference motion vectors of the reference block, a reference motion vector that refers backward in the display order with respect to the current picture.
4. The moving picture decoding method according to claim 1 ,
wherein in said calculating, when the reference block does not have a reference motion vector, a candidate motion vector is calculated using, from among reference motion vectors of another reference block located backward in display order with respect to the current picture, a reference motion vector that refers forward in the display order with respect to the current picture.
5. The moving picture decoding method according to claim 4 ,
wherein in said calculating, when the reference block does not have the reference motion vector and when the other reference block does not have the reference motion vector that refers forward in the display order with respect to the current picture, the candidate motion vector is calculated using a reference motion vector of the other reference block that refers backward in the display order with respect to the current picture.
6. A moving picture decoding apparatus of decoding a current block to be decoded which is included in a current picture to be decoded, said moving picture decoding apparatus comprising:
one or more processors; and
storage coupled to the one or more processors,
wherein the one or more processors is configured to:
determine a display order between the current picture and each of a plurality of reference pictures included in at least one of a first reference picture list and a second reference picture list, the display order being determined using an index of each of the reference pictures;
determine whether or not a reference block has two reference motion vectors that refer forward in the display order with respect to the current picture, the reference block being included in one of the reference pictures, the one of the reference pictures being located forward in the display order with respect to the current picture;
calculate, when the reference block has the two reference motion vectors that refer forward in the display order with respect to the current picture, (i) a first candidate motion vector of the current block by scaling one of the two reference motion vectors and (ii) a second candidate motion vector of the current block by scaling the other one of the two reference motion vectors;
generate a candidate motion vector list in which candidate motion vectors, including the first candidate motion vector and the second candidate motion vector, respectively correspond to values of a candidate motion vector index in one-to-one relationship;
decode index information for identifying a candidate motion vector to be used in decoding;
decode difference information about a difference between a current motion vector of the current block included in the current picture and the candidate motion vector to be used in decoding;
calculate the current motion vector by adding the difference information and, from among the candidate motion vectors included in the candidate motion vector list, the candidate motion vector to be used in the decoding, which is identified by the candidate motion vector index having a same value as a value indicated by the index information; and
decode the current block using the current motion vector.