1. A method comprising: setting, by a prediction generator, a first prediction motion vector and a second prediction motion vector, wherein the first prediction motion vector is derived from a left neighboring region of a block to which a motion vector to be decoded is associated, and wherein the second prediction motion vector is derived from an above neighboring region of the block to which the motion vector to be decoded is associated; comparing, by a comparator, the first prediction motion vector and the second prediction motion vector; and updating, by a controller, the second prediction motion vector using a third prediction motion vector when the first prediction motion vector is equal to the second prediction motion vector, an available third prediction motion vector exists in a video image, and a stop condition associated with a limit on a total number of predictions for at least one prediction generation process is not satisfied, wherein the first, second, and third prediction motion vectors are based on motion vectors at different positions, wherein when the stop condition is satisfied regardless of whether additional prediction motion vectors exist in the video image or one or more of additional prediction motion vectors are not equal to the first prediction motion vector, the prediction generation process ends.