A Modified Octagon-Based Search Algorithm for Fast Block Motion Estimation

Based on zero-block detection method in H.264/AVC, the directional characteristic of the SAD(Sum of Absolute Differences Distortion), the centre-biased characteristic of motion vectors, and by analyzing the characteristics of OCTBS(Octagon-based Search), MOCTBS (Modified Octagon-based Search) algorithm is proposed in this paper. Firstly, MOCTBS employs small octagon pattern to judge if the MBD (Minimum Block Distortion) point located in the circle of one pixel around the initial search centre. If the MBD point does not locate in the one pixel circle around the initial search centre or no zero-block was detected, large octagon pattern will be used in the next search step. In order to speed up the motion estimation, zero-block detection method is used in the whole processing of block-matching motion estimation to terminate the search process as early as possible. Experimental results show that MOCTBS can speed up the motion estimation process greatly under the same encoding efficiency compared to OCTBS, especially for those video sequences with simple and slow motion vectors.