Fast sub-pel motion vector prediction via block classification

A technique to predict the optimal sub-pel motion vector (MV) position based on integer-pel MVs is investigated in this work. Although it is possible to find the optimal MV position by fitting a local error surface using integer-pel MVs, the minimum of the error surface may fall outside of the region of interest. By analyzing the behavior of the error surface, we propose a classification scheme that divides blocks into regular and irregular types. For a regular block, we adopt the traditional error surface model and solve its minimum as the predicted sub-pel MV position. For an irregular block, we developed a novel prediction scheme to predict the optimal sub-pel MV position. Experimental results are given to show the low complexity and good RD performance of the proposed sub-pel MV prediction scheme.