Patent ID: 7940845

Claim:
A motion vector determining method for determining a motion vector of a current block included in a current picture, said motion vector determining method comprising: specifying, when a co-located block has two motion vectors, only one motion vector out of the two motion vectors, the co-located block being located in a motion compensated second picture at the same position that the current block is located in the current picture, the motion compensated second picture being a picture following the current picture in display order; and determining the motion vector of the current block, using the specified one motion vector, wherein, in the case where (i) a first motion vector of the two motion vectors of the co-located block refers to a first reference picture preceding the motion compensated second picture in display order and (ii) a second motion vector of the two motion vectors of the co-located block refers to a second reference picture preceding the motion compensated second picture in display order, the first motion vector is specified in said specifying of only one motion vector, wherein the first motion vector appears in a bitstream earlier than the second motion vector, and wherein the first reference picture and the second reference picture are different pictures.