A Fast Search Algorithm for Sub-Pixel Motion Estimation in H.264

We propose the advanced sub-pixel block matching algorithm to reduce the computational complexity by using a statistical characteristic of SAD (Sum of Absolute Difference). Generally, the probability of the minimum SAD values is highest when a searching point has one pixel distance from the reference point. Thus, we can overcome high computational complexity problem by reducing the searching area. The main concept of proposed algorithm is one of the fast searching algorithms based on TSS (Three Step Search) method. First, we find three minimal SAD points of all nine searching points on integer distance and then we obtain two minimal SAD points on 1/2-pixel between the second minimal SAD point and the first, and between the third and first, respectively. Finally, we can find matching point by comparing the SAD values among six points which are on triangle from the first minimal SAD point and two 1/2-pixel points including 1/4-pixels. The proposed algorithm in this paper needs only 14 searching points in sub-pixel mode, whereas the conventional TSS method needs total 25 searching points. Therefore, this algorithm improves the processing speed as 51%.