1. A method of deriving a motion vector of a bi-predictive block based on a list0 motion vector of a co-located block in a reference picture using a bit operation, comprising: selecting the list0 motion vector of the co-located image block for the bi-predictive image block as a motion vector for deriving motion vectors of the bi-predictive image block if the co-located image block has a list1 and a list0 motion vector; and deriving at least one motion vector of the bi-predictive block by applying a bit operation to the selected motion vector.