基于Delaunay三角化的指纹匹配方法

将计算几何的三角划分方法引入指纹匹配，研究了一种基于DT（Delaunay triangulation）网的指纹匹配方法．通过对细节点的拓扑结构进行DT划分，把空间上位置相近的细节点按照一定规则相连，得到三角形网格．然后基于该网格寻找若干参考点对，并根据获得的参考点对将两幅指纹图像进行姿势调整．最后使用获得的参考点对实现基于点模式的指纹匹配．算法在第1届中国生物特征识别竞赛指纹组的测试结果证明了有效性．     

A deformable model for fingerprint matching

The process of automatic fingerprint matching is affected by the nonlinear deformation introduced in the image during fingerprint sensing. Given several template impressions of a finger, we estimate the “average” deformation of each template impression by comparing it with the rest of the impressions of that finger. The average deformation is developed using the thin plate spline (TPS) model and is based on minutia point correspondences between pairs of fingerprint impressions. The estimated average deformation is utilized to pre-distort the minutiae points in the template image before matching it with the minutiae points in the query image. We show that the use of an average deformation model leads to a better alignment between the template and query minutiae points. An index of deformation is proposed for choosing the deformation model with the least variability arising from a set of template impressions corresponding to a finger. Our experimental data consists of 1600 fingerprints corresponding to 50 different fingers collected over a period of 2 weeks. It is shown that the average deformation model leads to an improvement in the alignment between impressions originating from the same finger.     

Fingerprint matching based on global alignment of multiple reference minutiae

Fingerprint matching is an important problem in fingerprint identification. A set of minutiae is usually used to represent a fingerprint. Most existing fingerprint identification systems match two fingerprints using minutiae-based method. Typically, they choose a reference minutia from the template fingerprint and the query fingerprint, respectively. When matching the two sets of minutiae, the template and the query, firstly reference minutiae pair is aligned coordinately and directionally, and secondly the matching score of the rest minutiae is evaluated. This method guarantees satisfactory alignments of regions adjacent to the reference minutiae. However, the alignments of regions far away from the reference minutiae are usually not so satisfactory. In this paper, we propose a minutia matching method based on global alignment of multiple pairs of reference minutiae. These reference minutiae are commonly distributed in various fingerprint regions. When matching, these pairs of reference minutiae are to be globally aligned, and those region pairs far away from the original reference minutiae will be aligned more satisfactorily. Experiment shows that this method leads to improvement in system identification performance.     

一种新的形变指纹匹配方法

提出了一种基于细节点局部配准的形变指纹匹配方法。首先,结合细节点的纹理信息以及结构信息获取多个参照点;然后依据选取的多参照点实现模板指纹图像与输入指纹图像的全局配准从而获得指纹之间的公共区域;将公共区域内的细节点与它们最近的参照点聚类组合,形成多个分组,并将各分组内的细节点以对应的参照点为极点转化到极坐标系下建立指纹的局部对应性;最后,采用界限盒约束条件实现指纹匹配。实验结果表明,基于局部配准的指纹匹配方法对形变指纹匹配具有较好的鲁棒性,能较大提升指纹的识别性能。     

A New Autom ated Fingerprint Identification System

A new automated fingerpring identification system is proposed.In this system,based on some local properties of digital image,the shape and minutiae features of fingerprint can be extracted from the grey level image without binarizing and thinning.In query,a latent fingerprint can be matched with the filed fingerprints by shape and/or minutiae features.Matching by shape features is much faster than by minutiae.     

Fingerprint reconstruction: from minutiae to phase

Fingerprint matching systems generally use four types of representation schemes: grayscale image, phase image, skeleton image, and minutiae, among which minutiae-based representation is the most widely adopted one. The compactness of minutiae representation has created an impression that the minutiae template does not contain sufficient information to allow the reconstruction of the original grayscale fingerprint image. This belief has now been shown to be false; several algorithms have been proposed that can reconstruct fingerprint images from minutiae templates. These techniques try to either reconstruct the skeleton image, which is then converted into the grayscale image, or reconstruct the grayscale image directly from the minutiae template. However, they have a common drawback: Many spurious minutiae not included in the original minutiae template are generated in the reconstructed image. Moreover, some of these reconstruction techniques can only generate a partial fingerprint. In this paper, a novel fingerprint reconstruction algorithm is proposed to reconstruct the phase image, which is then converted into the grayscale image. The proposed reconstruction algorithm not only gives the whole fingerprint, but the reconstructed fingerprint contains very few spurious minutiae. Specifically, a fingerprint image is represented as a phase image which consists of the continuous phase and the spiral phase (which corresponds to minutiae). An algorithm is proposed to reconstruct the continuous phase from minutiae. The proposed reconstruction algorithm has been evaluated with respect to the success rates of type-I attack (match the reconstructed fingerprint against the original fingerprint) and type-II attack (match the reconstructed fingerprint against different impressions of the original fingerprint) using a commercial fingerprint recognition system. Given the reconstructed image from our algorithm, we show that both types of attacks can be successfully launched against a fingerprint recognition system.     

一种新的指纹匹配方法

针对基于点模式匹配的指纹匹配算法速度较慢的现状，设计了一种新的指纹匹配方法，即利用纹线匹配技术来寻找基准点对的指纹匹配算法．该算法首先基于指纹纹线的相似程度寻找一对基准特征点；然后根据基准点对的坐标，计算两幅指纹图象(模板图象、待识图象)的相对平移和旋转参数，并将待识图象相对于模板图象进行图象姿势纠正；最后使用坐标匹配的方法统计两幅图象能够匹配的特征点数目．以实现两枚指纹的匹配．实验证明．该算法匹配速度很快，误识率低，准确性高，并具有图象旋转平移不变性．对面积适中的指纹图象，匹配结果可以满足在线应用的需要．该算法有望发展成为一种实用、有效的指纹匹配技术．     

Improving automated latent fingerprint identification using extended minutia types

Latent fingerprints are usually processed with Automated Fingerprint Identification Systems (AFIS) by law enforcement agencies to narrow down possible suspects from a criminal database. AFIS do not commonly use all discriminatory features available in fingerprints but typically use only some types of features automatically extracted by a feature extraction algorithm. In this work, we explore ways to improve rank identification accuracies of AFIS when only a partial latent fingerprint is available. Towards solving this challenge, we propose a method that exploits extended fingerprint features (unusual/rare minutiae) not commonly considered in AFIS. This new method can be combined with any existing minutiae-based matcher. We first compute a similarity score based on least squares between latent and tenprint minutiae points, with rare minutiae features as reference points. Then the similarity score of the reference minutiae-based matcher at hand is modified based on a fitting error from the least square similarity stage. We use a realistic forensic fingerprint casework database in our experiments which contains rare minutiae features obtained from Guardia Civil, the Spanish law enforcement agency. Experiments are conducted using three minutiae-based matchers as a reference, namely: NIST-Bozorth3, VeriFinger-SDK and MCC-SDK. We report significant improvements in the rank identification accuracies when these minutiae matchers are augmented with our proposed algorithm based on rare minutiae features.     

一种快速的指纹参照点对选取方法研究

快速准确地确定匹配参照点对是实现基于点模式指纹识别的一个关键问题,针对该问题本文提出了一种基于脊线校准的确定匹配参照点对的新方法。该方法首先利用细节点间的距离、类型以及细节点与脊线样点之间构成的网状结构来构建新的局部特征向量,然后在这些结构特征向量空间中搜索最为相似特征向量,确定出最优匹配参照点对。实验结果表明,本文提出的算法不仅速度快,而且准确性也有了较大提高。     

一种鲁棒的指纹细节特征点匹配方法

指纹细节特征点匹配是指纹识别过程的核心部分,鲁棒的细节特征点匹配方法需要克服指纹的旋转、变形和真实特征点丢失的情况。该文通过引入支持模型来进行细节特征点匹配,获得了较好的结果。在对支持模型理论进行简单分析之后,详细介绍了所提出的一个鲁棒的基于支持模型的细节特征点匹配算法。该方法通过融合多个种子松弛匹配的结果,来获取每个细节特征点的约束支持。并通过每个对应点不同的支持度得到一一对应的细节特征点匹配结果。最后给出两个指纹细节特征点集的相似性水平。该算法具有较强的鲁棒性和稳定性,能够很好地解决指纹细节特征点匹配过程中存在的旋转、变形和真实细节特征点丢失等情况。最后给出的实验结果验证了该算法的有效性。     

Alignment-free cancelable fingerprint templates based on local minutiae information.

To replace compromised biometric templates, cancelable biometrics has recently been introduced. The concept is to transform a biometric signal or feature into a new one for enrollment and matching. For making cancelable fingerprint templates, previous approaches used either the relative position of a minutia to a core point or the absolute position of a minutia in a given fingerprint image. Thus, a query fingerprint is required to be accurately aligned to the enrolled fingerprint in order to obtain identically transformed minutiae. In this paper, we propose a new method for making cancelable fingerprint templates that do not require alignment. For each minutia, a rotation and translation invariant value is computed from the orientation information of neighboring local regions around the minutia. The invariant value is used as the input to two changing functions that output two values for the translational and rotational movements of the original minutia, respectively, in the cancelable template. When a template is compromised, it is replaced by a new one generated by different changing functions. Our approach preserves the original geometric relationships (translation and rotation) between the enrolled and query templates after they are transformed. Therefore, the transformed templates can be used to verify a person without requiring alignment of the input fingerprint images. In our experiments, we evaluated the proposed method in terms of two criteria: performance and changeability. When evaluating the performance, we examined how verification accuracy varied as the transformed templates were used for matching. When evaluating the changeability, we measured the dissimilarities between the original and transformed templates, and between two differently transformed templates, which were obtained from the same original fingerprint. The experimental results show that the two criteria mutually affect each other and can be controlled by varying the control parameters of the changing functions.     

Fingerprint warping using ridge curve correspondences

The performance of a fingerprint matching system is affected by the nonlinear deformation introduced in the fingerprint impression during image acquisition. This nonlinear deformation causes fingerprint features such as minutiae points and ridge curves to be distorted in a complex manner. A technique is presented to estimate the nonlinear distortion in fingerprint pairs based on ridge curve correspondences. The nonlinear distortion, represented using the thin-plate spline (TPS) function, aids in the estimation of an "average" deformation model for a specific finger when several impressions of that finger are available. The estimated average deformation is then utilized to distort the template fingerprint prior to matching it with an input fingerprint. The proposed deformation model based on ridge curves leads to a better alignment of two fingerprint images compared to a deformation model based on minutiae patterns. An index of deformation is proposed for selecting the "optimal" deformation model arising from multiple impressions associated with a finger. Results based on experimental data consisting of 1,600 fingerprints corresponding to 50 different fingers collected over a period of two weeks show that incorporating the proposed deformation model results in an improvement in the matching performance.     

基于图像质量分区的指纹特征提取

低质量指纹图像的特征提取和变形指纹的匹配是当前指纹识别研究中的两个主要问题。很多算法在特征提取时不区分高、低质量区域,结果在高质量区域耗费了过多的运算时间和计算资源。本文提出了一种基于图像质量分区的指纹特征提取方法,先用一种简单的图像区域质量计算方法评价各区域的图像质量,然后对高质量区域直接从灰度图像跟踪纹线、提取节点,对低质量区域执行传统的方向计算、增强、二值化和细化后提取特征。实验结果表明,该方法不仅提高了特征提取的速度,在准确性上也有所提高。     

Fingerprint matching by genetic algorithms

Fingerprint matching is still a challenging problem for reliable person authentication because of the complex distortions involved in two impressions of the same finger. In this paper, we propose a fingerprint-matching approach based on genetic algorithms (GA), which tries to find the optimal transformation between two different fingerprints. In order to deal with low-quality fingerprint images, which introduce significant occlusion and clutter of minutiae features, we design a fitness function based on the local properties of each triplet of minutiae. The experimental results on National Institute of Standards and Technology fingerprint database, NIST-4, not only show that the proposed approach can achieve good performance even when a large portion of fingerprints in the database are of poor quality, but also show that the proposed approach is better than another approach, which is based on mean-squared error estimation.     

Fingerprint matching from minutiae texture maps

The fingerprint matching using the original FingerCode generation has proved its effectiveness but it suffers from some limitations such as the reference point localization and the recourse to the relative fingerprint pre-alignment stage. In this paper, we propose a new hybrid fingerprint matching technique based on minutiae texture maps according to their orientations. Therefore, rather than exploiting the eight fixed directions of Gabor filters for all original fingerprint images filtering process, we construct absolute images starting from the minutiae localizations and orientations to generate our weighting oriented Minutiae Codes. The extracted features are invariant to translation and rotation, which allows us avoiding the fingerprint pair relative alignment stage. Results are presented demonstrating significant improvements in fingerprint matching accuracy through public fingerprint databases.     

Direct gray-scale minutiae detection in fingerprints

Most automatic systems for fingerprint comparison are based on minutiae matching. Minutiae are essentially terminations and bifurcations of the ridge lines that constitute a fingerprint pattern. Automatic minutiae detection is an extremely critical process, especially in low-quality fingerprints where noise and contrast deficiency can originate pixel configurations similar to minutiae or hide real minutiae. Several approaches have been proposed in the literature; although rather different from each other, all these methods transform fingerprint images into binary images. In this work we propose an original technique, based on ridge line following, where the minutiae are extracted directly from gray scale images. The results achieved are compared with those obtained through some methods based on image binarization. In spite of a greater conceptual complexity, the method proposed performs better both in terms of efficiency and robustness     

基于贪心算法进行三角剖分的印鉴匹配方法

将计算几何中平面点集的三角剖分方法-贪心算法引入印鉴识别,研究了一种基于三角网格的印鉴匹配方法.通过对细节点的拓扑结构进行三角划分,把空间上位置相近的细节点按照一定的规则相连,得到三角形网格.然后基于该网格寻找若干参考点对,并根据获得的参考点对将两幅印鉴图像进行姿势调整.最后使用获得的参考点对实现基于点模式的印鉴匹配,经分析该方法是一种行之有效的印鉴匹配方法.     

Fingerprint-Based Fuzzy Vault: Implementation and Performance

Reliable information security mechanisms are required to combat the rising magnitude of identity theft in our society. While cryptography is a powerful tool to achieve information security, one of the main challenges in cryptosystems is to maintain the secrecy of the cryptographic keys. Though biometric authentication can be used to ensure that only the legitimate user has access to the secret keys, a biometric system itself is vulnerable to a number of threats. A critical issue in biometric systems is to protect the template of a user which is typically stored in a database or a smart card. The fuzzy vault construct is a biometric cryptosystem that secures both the secret key and the biometric template by binding them within a cryptographic framework. We present a fully automatic implementation of the fuzzy vault scheme based on fingerprint minutiae. Since the fuzzy vault stores only a transformed version of the template, aligning the query fingerprint with the template is a challenging task. We extract high curvature points derived from the fingerprint orientation field and use them as helper data to align the template and query minutiae. The helper data itself do not leak any information about the minutiae template, yet contain sufficient information to align the template and query fingerprints accurately. Further, we apply a minutiae matcher during decoding to account for nonlinear distortion and this leads to significant improvement in the genuine accept rate. We demonstrate the performance of the vault implementation on two different fingerprint databases. We also show that performance improvement can be achieved by using multiple fingerprint impressions during enrollment and verification.     

一种基于结构匹配的指纹匹配算法

提出了一种基于结构匹配的指纹匹配算法,不仅考虑了指纹的全局特性而且利用了指纹局部结构的平移和旋转不变性。该算法可克服在采集指纹图像时由于非线性形变所引起的细节点的位置、细节点的方向及指纹图像中细节点之间距离改变产生的影响,降低了匹配算法的拒识率。试验结果表明所提出的方法确实提高了指纹匹配算法的有效性。     

基于Matlab实现的指纹图像细节特征提取

指纹图像的特征提取是指纹识别的关键,而指纹匹配通常基于细节点匹配.介绍了一套基于Matlab实现的指纹细节特征提取方法,并给出了去伪算法.指纹特征提取是从细化后的指纹图中得到细节特征点(即端点和分叉点),此特征点含有大量的伪特征,既耗时又影响匹配精度.采用了边缘去伪和距离去伪,使得特征点去伪前后减小了近1/3,然后提取可靠特征点信息,以便实现指纹匹配.实验证明,用Matlab实现的这种方法,既简单快速,而且具有较高的准确率.