【作者】 韩涛；

【导师】 朱明富；

【作者基本信息】 华中科技大学 ， 系统工程， 2005， 硕士

【摘要】 自动指纹识别技术近些年取得了长足的发展并广泛应用于各种个人身份识别系统中。然而,指纹识别技术的各个环节在实际应用中还存在一些问题,如低质量指纹图像的增强、指纹特征的选取等问题没有得到很好的解决。指纹识别大致可以分为三个阶段:指纹图像预处理,指纹特征提取和指纹特征匹配。对前两个阶段有针对性地进行了算法研究,包括指纹图像的方向图计算、方向滤波、二值化、纹线修复、特征提取等。提出一种基于Sobel 算子的梯度场平滑的方法求解块方向图。该方法增加了对纹线曲率变化较大区域的敏感度,因此求出的块方向图能更准确地反映整幅指纹图像的纹线走向。针对该方法得到的块方向图会出现奇异点漂移的现象,使用一种低通滤波的办法来修正块方向图。应用自适应理论和模糊理论,提出几种确定二值化阀值的具体方法。这些方法虽然由简到繁,但是其灰度的局部适应性和方向的匹配性越来越强,因而得到的阀值越来越准确。在修复指纹纹线从而去除伪特征的处理过程中,提出了指纹图像断裂纹线的修复方法。设计出断点搜索算法和方向均分法、窗口制约法、改进的窗口制约法等修复算法。这些算法易于软件编程实现,减少了修复步骤,扩大了修复范围,有效地去除了伪末梢特征点,对细化指纹的断裂有很好的修复效果。提出了一种基于8邻域编码表的指纹特征提取方法。在分析了指纹细节特征的结构特性之后,创建表格以反映编码与类型、末梢点方向、分叉点方向、连续点方向以及方向与坐标增量等信息。利用这些表,可以很容易地对细化后的二值纹线骨架进行跟踪,找到指纹细节特征。总的来说,对指纹识别技术中的预处理和特征提取环节进行了广泛的研究和有益的探讨。更多还原

【Abstract】 The technology of fingerprint identification, widely applied in a variety of situations of personal identity verification and recognition, has made a great progress. However, there are still challenging problems, such as enhancement of poor quality images, extraction of fingerprint features, which remain not well-solved. The process of fingerprint identification can be divided into three steps: preprocessing of fingerprint images, feature extraction and feature matching. The thesis focused on algorithms in first two steps, including direction calculation, binarization, lines healing and feature extraction. A block direction calculation method was proposed, which used the gradient smoothness based on Sobel operator. This algorithm enhanced the sensitivity to the areas in which the curvature of the lines in fingerprint image changed more than in other ones. So the block direction obtained by this method can correspond to the tendency of the lines in the whole image precisely. In addition, a low-pass filter was used to revise the direction in order to deal with the singularities excursion. With the use of the theory of self-adaptation and fussy, several methods of setting gate of binarization were presented. Although the methods were more and more complex, the local adaptability of gray scale and the matching ability of the direction became stronger and stronger. As a result, the gate obtained by these methods got more and more precise. During the lines healing in order to get rid of the false features, a healing method of broken lines in fingerprint image was introduced. Direction average-divided algorithm, window constraint algorithm and improved window constraint algorithm were designed respectively for the different kind of breaks based on the existing method’s merits. These algorithms made the healing process more complete and efficient, were convenient for programming, improved the rid ratios of false ending feature and performed much well on healing the broken lines. A feature extraction method was also proposed, which was based on the coding table of adjacent regions with 8 neighbors. The table about coding and type, ending direction, bifurcation direction, series direction, increment of coordinates in directions were established and made it easy to track the lines’framework to find the features in the fingerprint image. In a word, a lot of fruitful attempts and significant progress on the algorithms of fingerprint identification have been made.更多还原