以视频压缩标准H.264联合开发模型(JM)中的运动估计算法UMHexagonS为基础, 提出了一个新的快速整像素运动估计算法来改进压缩编码性能。在起始搜索点预测部分, 提出了新的预测运动矢量(MV)检测顺序, 以提高起始搜索点的准确度; 在全局搜索部分提出了自适应全局搜索方法, 根据准确度最高的两个预测MV之间的关系, 适当跳过非对称十字型模板搜索和非均匀多重六边形模板搜索, 并通过对不同序列的测试, 验证了判断准则的可行性与准确性。根据实际序列中最佳MV相对起始点的分布, 提出了改进5×5搜索。另外, 增加了针对子宏块的提前终止策略, 在不增加额外运算量的前提下, 进一步减少了运动估计开销。实验结果表明, 相对UMHexagonS算法, 提出的改进算法使搜索点总数平均减小了83.80%, 信噪比平均下降了0.021 dB, 或输出码率等效增加了0.46%。该算法有效降低了运动估计的运算量, 而只带来了很小的编码性能下降, 且对不同运动强度的视频序列具有均匀的算法效果。

On the basis of the UMHexagonS algorithm used in the Joint Model(JM) for H.264, a new fast algorithm on integer pixel motion estimation was proposed to improve the video encoding characteristics. A new order of checking predicted Motion Vector(MV) was proposed in the predicting starting search point to promote the accuracy of starting search point. Then, a self-adaptive global search method was proposed for the global search, by which the unsymmetrical-cross search and uneven multi-hexagon-grid search could be skipped based on the relationship between two predicted MVs with highest accuracy, and the feasibility and accuracy of this judging method was verified through tests on a number of different sequences. Meanwhile, an improved 5×5 search method was presented according to the distribution of best MV relative to the starting search point and a new early termination technique for sub-macroblock was added to further reduce the cost of motion estimation without additional computation. According to the experiment results, the proposed algorithm reduces the total number of search points by 83.80% and the Peak Signal to Noise Ratio(PSNR) about 0.021 dB on average and increases an average increment of 0.46% on equivalent bitrates as compared with that of original UMHexagonS algorithm. With a negligible performance degradation, the proposed algorithm reduces the computation of motion estimation effectively and offers a well-distributed effect on sequences with different motion intensities.