【作者】 李单单；

【导师】 朱冰莲；

【作者基本信息】 重庆大学 ， 信号与信息处理， 2007， 硕士

【摘要】 计算机技术和网络技术的发展和普及,大大推动了视频技术的发展和应用,数字视频技术在当前的信息社会中日益发挥着重要的作用。MPEG-4作为新一代的视频压缩编码标准,由于其本身具有诸多的优越性能和高效的压缩效率,使其在Internet多媒体应用、实时可视通信等诸多方面得到了广泛应用。影响MPEG-4视频压缩编码质量和效率的因素很多,运动估计是其中最有影响力的因素之一。运动估计越准确,解码出来的视频图像质量越好。而且运动估计在整个视频压缩编码系统中耗时最多。因此快速、准确的运动估计算法是视频压缩编码技术的研究重点。本文首先对MPEG-4标准的特性作了一个简要的介绍,然后对MPEG-4中的关键算法——基于块匹配的运动估计的基本原理和要素进行了阐述,并分析了一些快速算法的特点,在此基础上分别对运动估计算法从速度和准确度两个方面进行改进:提出了基于内部预测的快速菱形算法,通过对菱形算法进行内部预测从而减少搜索点数,并利用运动矢量的相关性来进行起点预测,将宏块划分成不同的运动类型从而选用不同的搜索方式。实验结果表明此算法大大提高了运动估计的速度。传统的快速算法都是基于误差函数呈单峰分布的假设,在搜索过程易陷入局部最优,从而导致搜索精度不高,视频编解码质量下降。本文又提出的基于模拟退火的自适应运动估计算法,它针对传统快速算法的不足,在搜索的过程中加入了模拟退火,并引人了自适应机制,根据宏块的特性而设置参数,因而具有很强的自适应性,在模拟退火结束后还进行了梯度下降搜索,进一步提高匹配的精度。实验结果表明此算法极大的降低了搜索陷入局部最优的可能,提高了视频编解码质量。在应用中可以根据对速度和质量的侧重点不同在两种运动估计算法中进行选择。更多还原

【Abstract】 With the development and popularization of computer and network technology, video technology has been widely applied to various applications and plays a more and more important role nowadays. MPEG-4 is a popular video compression coding standard, which is applied to plenty of relative areas such as internet multimedia, real-time visual communication and etc. because of its powerful performance and high compression efficiency.Among the factors which influence the coding quality and efficiency for MPEG-4, motion estimation technology is the most important one. It is known that the accuracy of motion estimation usually determines the quality of decoded images to a great extent. However, motion estimation contributes to the most part of computational load in the whole video coding system. Thus research on efficient motion estimation algorithm becomes a focus in video coding field.At first, this paper gives an overview of the specialties of MPEG-4,then introduce the basic theory and key points of its core technology, which is block-matching motion estimation. On the basis of the analysis on popular fast block-matching algorithms, two novel algorithms are respectively proposed, aiming at the improvement of quality and speed.In this paper, a new algorithm called inner predictive diamond fast motion estimation is proposed, applying inner predictive technique to speed up original diamond search. It also takes advantage of the correlation of adjacent macro-blocks to predict the initial search point, and uses appropriate search strategy for different motion style macro-blocks. Experimental results show that the proposed algorithm greatly improves searching speed.Traditional estimation algorithms based on the local unimodal error surface assumption have an inherent shortcoming of getting into the local optima, which leads to degeneration on the quality of video images. Therefore, an adaptive motion estimation algorithm using simulated annealing is proposed to overcome this shortcoming. It is highly adaptive since its parameters are setup according to the characteristic of macro-block in search process. Moreover, there is refined search after SA to enhance matching precision. The simulations show that this proposed algorithm is robust against local minima and improves searching accuracy remarkably. In conclusion, it depends on the different requirement between quality and speed to choose the more suitable one of above proposed algorithms.更多还原