1. A method of processing video data, comprising: receiving first image data representing a first frame; identifying a plurality of feature points in the first frame; receiving a second image data representing a second frame; deriving a motion vector corresponding to each of the feature points; selecting a first one of the motion vectors as the current vector A and selecting a second one of the motion vectors as the current vector B; and comparing vector A with vector B based on their vector magnitude ratio and their angular difference.