随着近年来多媒体技术的飞速发展，许多应用领域对视频图像的实时压缩提出了更高的要求，快速、高效的压缩算法是解决这一问题的关键。运动估计作为实现视频压缩的核心技术，也是压缩编码中运算最复杂、最耗时的环节，因此，快速运动估计算法一直是视频压缩领域的研究热点。 本文首先阐述了基于块匹配的运动估计的基本原理，介绍了全搜索法和几种典型的块匹配运动估计快速算法，分析了它们各自的技术特点，通过实验数据定量地评价了各算法的优缺点，在此基础上总结了提高运动估计搜索效率的一般思路。然后重点介绍了本文提出的一种改进的运动矢量场自适应运动估计算法，该算法基于MVFAST分级搜索的思想，优化了运动强度的划分方法，引入了相对运动类型的划分来对大运动块自适应地选择搜索模式，搜索中尽量使用简单策略，并自适应地提前结束搜索。实验结果表明，该改进算法与MVFAST和PMVFAST算法相比，在图像质量稍有下降的前提下，具有搜索速度上的明显优势。最后，针对H.263编码器，研究了在软件实现时提高运动估计算法效率的一些优化技术，详细总结了一些经典的优化方案，给出了一种基于位标识的重复搜索点的识别方法，提出了根据运动矢量各向非均匀分布特性设置模板内各搜索点顺序的思想，并通过实验验证了各优化方案的有效性。

With the fast development of multimedia techniques, there are many areas need more efficient real-time compression techniques for digital image processing. Fast and efficient compression algorithm is the key for this problem. Motion estimation is rather complex in computation and occupies much time of video compression. Fast motion estimation algorithm has always been a favorite to the researchers in the related field. Firstly, this thesis expatiates the essential principle of the motion estimation based on block matching, introduces Full Search method and several typical motion estimation fast algorithms based on block matching, analyzes each characteristic, and evaluates their advantage and disadvantage through the data get from experiment, then to sum up the universal way to improve the efficiency of motion estimation. Secondly, an improved motion estimation fast algorithm based on MVFAST algorithm is proposed. The new algorithm bases on classifiable search method in MVFAST, improves the classification of motion intensity, imports relative motion intensity classification of fast moved block to adaptively choose search strategy, uses more simple search method, and finishes search adaptively. The result of experiments proved that this algorithm can improve the search speed at the even same video quality in contrast to MVFAST and PMVFAST algorithm. At last, the thesis aimed at H.263 coder, studied some optimization techniques for improving the efficiency of motion estimation algorithm in software implementation, summarized several typical optimization schemes, presented a succinct and efficient method based on bit sign to avoid repetition of search point，proposed to set the search order of points in one template based on motion vector’s unequal distribution in each direction, and compared the performance of H.263 coder before and after above-mentioned optimization.