【作者】 李海燕；

【导师】 卢志茂；

【作者基本信息】 哈尔滨工程大学 ， 信号与信息处理， 2011， 硕士

【摘要】 图像分割可看作是一种把已获得的图像区分成若干个子图的技术,子图被认为是有意义的区域并且区域与区域之间必然是互不重合的。近年来,图论(Graph Theory)是研究图像分割的一个热点方面。它把图像分割的问题转化成更为灵活的图划分问题,成为全局最优的选取。归一化割(Normalized cut, Ncut)是基于图论的图像分割方法当中的一种,被看作规范化的准则。它可以融合输入图像的不同特征,同时可计算分割得到的不同目标区域之间的差异性和同一目标区域内部的相似性。但是,Ncut本身仍是存在某些问题,譬如说计算量大、过分割以及欠分割。其中,计算量大的实际问题会影响Ncut在现实中的应用。分水岭是一种很成熟的分割方法,算法比较简单,有很快的计算速度。而且处理之后的物体轮廓线封闭,能准确地定位,对微弱边缘也能得到良好的响应。它的缺点是存在着过分割的现象。针对两者的优点和缺点,本文提出一种将二次分水岭和Ncut相结合的图像分割方法。先利用二次分水岭对输入图像进行预处理,将得到的小区域看做像素点做为Ncut算法的输入。这种方法有效地解决了Ncut方法计算量大的问题。本文重点研究内容：(1)提出用二次分水岭和Ncut相结合的图像分割方法。用二次分水岭对输入图像进行预处理,将得到的每个小区域看做一个像素点。在此基础上构造加权图,做为Ncut算法的输入。实验证明,本文方法分割结果良好,速度很快。(2)为有效地解决二次分水岭分割结果当中的“0”边界,本文提出几种去边界方法,并通过实验获得最优方案,即将标记为0的像素点划分到与其八邻域相似度最大的点所在的小区域。(3)采用与欧氏距离联系密切的LUV颜色模型和空间位置信息构造权值矩阵,探索已有构造方法造成分割效果存在差异的原因,并通过实验验证。(4)用二次分水岭和Ncut相结合的分割方法先后与传统的Ncut算法和基于meanshift和Ncut结合的分割方法对比。选取多组图像,实验结果表明,与传统的方法相比本文在运行时间和分割效果方面都有显著提高；与基于nean shift和Ncut结合的分割方法相比,分割效果相近,但是本文方法耗时更少。更多还原

【Abstract】 Image segmentation is a technology that can divide an acquired image into a number of significant areas, and also, the areas are not overlapped.In recent years, graph theory is a hot research area of image segmentation. It transforms image segmentation into a flexible graph partitioning problem that selects information form the global graph. Ncut (Normalized cut) based on graph theory is one of the image segmentation methods. It is a standardized criterion. It can merge the different characteristics of the input images, and calculate the difference of the nodes among different small areas and similarity of the nodes within the same target region. However, there are still some problems of Ncut. For instance, it has large computation, over-segmentation and under segmentation. Large computation will affect the application of Ncut in reality.The watershed is a well developed algorithm which has the advantages of fast computing speed, and closed outline of objects. It also can accurately position and get a good response of the weak edge. However, it has a drawback of over-segmentation.In this paper, a method combining second watershed and Ncut algorithm is proposed to make use of their advantages and overcome their shortcomings. The second watershed is used to preprocess the input image. In this case, small areas are got and set as the input of Ncut algorithm, so the computing time of the method is greatly reduced.The main contents of this paper are as follows.Firstly, we combine the second watershed and Ncut algorithm by considering each micro segment after the second watershed as a node in the graph. Since the number of nodes in the graph is reduced, the total running time of the segmentation is greatly reduced. In addition, experiments also show that the combined method also obtains better partitioning results compared with the Ncut algorithm.Secondly, to solve the problem of border line (labeled by zeros) generated by the second watershed, several methods are proposed and fully discussed. We first look for the maximal similar pixel among the neighboring pixels (eight-neighborhood) of the zero’s corresponding pixel, and then the zeros are classified as the areas which the maximal similar pixels belong to. Thirdly, we construct the weight matrix based on the color information of LUV system and distance information. Moreover, the partitioning differences caused by existing weight matrix methods are analyzed and tested.Fourthly, the combined scheme proposed in this paper is campared with the traditional Ncut algorithm and the mean shift Ncut method separately. Simulation results prove that our scheme not only greatly reduces the running time but also acquires good segmentation effect campared with the traditional Ncut algorithm. And our plan runs faster than the mean shift Ncut method as well.更多还原