Image coding method and image coding apparatus
An image coding method includes: selecting a first picture from plural pictures; setting a first temporal motion vector prediction flag which is associated with the first picture and is a temporal motion vector prediction flag indicating whether or not temporal motion vector prediction is to be used, to indicate that the temporal motion vector prediction is not to be used, and coding the first temporal motion vector prediction flag; coding the first picture without using the temporal motion vector prediction; and coding a second picture which follows the first picture in coding order, with referring to a motion vector of a picture preceding the first picture in coding order being prohibited.
1. An image decoding method comprising:
obtaining, from a header of a slice included in a first picture, a temporal motion vector prediction flag indicating whether or not temporal motion vector prediction is to be performed on the first picture;
judging, using the obtained temporal motion vector prediction flag, whether or not the temporal motion vector prediction is to be performed on the first picture, the temporal motion vector prediction using a temporal motion vector predictor derived from a motion vector of a co-located reference picture;
when said judging judges that the temporal motion vector prediction is to be performed on the first picture, (i) creating a first list of motion vector predictors that includes at least one temporal motion vector predictor derived from the motion vector of the co-located reference picture, (ii) obtaining a first parameter from a bitstream, the first parameter indicating a first motion vector predictor included in the first list, (iii) decoding the first picture using the first motion vector predictor indicated by the first parameter, and (iv) decoding a second picture following the first picture in decoding order by using the temporal motion vector prediction using the temporal motion vector predictor derived from the motion vector of the co-located reference picture preceding the first picture; and
when said judging judges that the temporal motion vector prediction is not to be performed on the first picture, (i) creating a second list of motion vector predictors that does not include the temporal motion vector predictor derived from the motion vector of the co-located reference picture, (ii) obtaining a second parameter from a bitstream, the second parameter indicating a second motion vector predictor included in second list, (iii) decoding the first picture using the second motion vector predictor indicated by the second parameter, and (iv) decoding the second picture by using the temporal motion vector prediction using the temporal motion vector predictor derived from a motion vector of the first picture and without using the motion vector of the co-located reference picture preceding the first picture,
wherein a number of the motion vector predictors included in the first list and a number of the motion vector predictors included in the second list are same.