Patent ID: 7742526

Claim:
A picture decoding method for decoding a coded picture, said picture decoding method comprising: a decoding step of: decoding, with a decoding unit, a co-located block which is a block included in a picture that is different from a current picture to be decoded and located identically to a current block to be decoded, using a motion vector of the co-located block and a reference picture corresponding to the motion vector of the co-located block; generating two motion vectors for the current block, based on the motion vector of the co-located block which is a block included within a previously decoded picture and co-located with the current block; and decoding the current block by performing motion compensation on the current block in direct mode using the generated two motion vectors for the current block and two reference pictures which correspond to the generated two motion vectors for the current block, wherein in the case where the co-located block in the previously decoded picture has been decoded using only one motion vector, which is a backward motion vector, and a backward reference picture which corresponds to the only one motion vector, the backward reference picture being a reference picture located after the previously decoded picture in display order, the backward motion vector being a motion vector that refers to a picture located after the previously decoded picture in display order, and where both the current picture to be decoded and the previously decoded picture are B-pictures, and the only one motion vector used for decoding the co-located block which is included within the previously decoded picture that is the B-picture is the backward motion vector, in said decoding step: the two motion vectors to be used for decoding the current block are generated by scaling the only one motion vector used for decoding the co-located block, using a difference between information indicating display order of pictures, and one of the generated two motion vectors refers to the previously decoded picture that is the B-picture.