Motion estimation is the most time-consuming stage in video compression coding. The video coding standard H. 264 has adopted the hybrid Unsymmetrical-cross Multi-hexagon-grid Search (UMHexagonS) algorithm as its fast motion estimation algorithm. The UMHexagonS algorithm is introduced in details and is improved in three aspects. Firstly, an adaptive threshold for early termination is added. Secondly, the 5 x 5 spiral search is replaced with a new search mode to reduce the number of the search points. Thirdly, the Multi-hexagon-grid Search is changed to Multi-tenpoints-grid Search. The algorithm is implemented and verified in JM10. 2. Results show that the improved algorithm can save about 7%-14% motion estimation time than the original one while keeping the similar picture quality.%运动估计是视频压缩编码中消耗时间最多的部分.H.264标准采纳混合非对称十字多六边形格点搜索(UMHexagonS)算法作为其快速运动估计算法.详细介绍了UMHexagonS算法,并从三个方面对算法进行了改进:一是增加一个自适应的提前终止判决门限,二是用一种新的搜索方式替代5×5螺旋搜索,减少搜索点数,三是将多层六边形搜索修改为多层十点搜索.在测试模型JM10.2上进行了算法验证,测试结果表明,在图像质量几乎不变的情况下,改进的算法比原算法节省了7％ -14％的运动估计时间.
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