On accurate orientation extraction and appropriate distance measure for low-resolution palmprint recognition

Orientation feature has been demonstrated to be one of the most effective features for low resolution palmprint recognition. In this paper, using steerable filter, we investigate the accurate orientation extraction and appropriate distance measure problems for effective palmprint recognition. First, we use high order steerable filter to extract accurate continuous orientation, and quantify it into discrete representation. Then, for effective matching of accurate orientations, we propose a generalized orientation distance measure. We further extend the distance measure for matching of discrete orientations, and show that several existing distance measures can be viewed as its special cases. Experimental results on both Hong Kong PolyU and CASIA palmprint databases show that the proposed method can obtain state-of-the-art verification accuracy. With the support of a look up table, the proposed method also enables small template size and satisfactory matching speed for practical applications.     

Fast palmprint identification with multiple templates per subject

Palmprint identification system commonly stores multiple templates for each subject to improve the identification accuracy. The system then recognizes a query palmprint image by searching for its nearest neighbor from all of the templates. When applied on moderate or large scale identification system, it is often necessary to speed up this process. In this paper, to speed up the identification process, we propose to utilize the intrinsic characteristics of the templates of each subject to build a tree, and then perform fast nearest neighbor searching with assistance of the tree structure. Furthermore, we propose a novel method to generate the ‘virtual’ template from all the real templates of each subject. The tree constructed by the virtual template and the real templates can further speed up the identification process. Two representative coding-based methods, competitive code and ordinal code, are adopted to demonstrate the effectiveness of our proposed strategies. Using the Hong Kong PolyU palmprint database (version 2) and a large scale palmprint database, our experimental results show that the proposed method searches for nearest neighbors faster than brute force searching, and the speedup becomes larger when there are more templates per subject in the database. Results also show that our method is very promising for embedded system based moderate scale and PC based large scale identification systems.     

Orientation selection using modified FCM for competitive code-based palmprint recognition

Coding-based methods are among the most promising palmprint recognition methods because of their small feature size, fast matching speed and high verification accuracy. The competitive coding scheme, one representative coding-based method, first convolves the palmprint image with a bank of Gabor filters with different orientations and then encodes the dominant orientation into its bitwise representation. Despite the effectiveness of competitive coding, few investigations have been given to study the influence of the number of Gabor filters and the orientation of each Gabor filter. In this paper, based on the statistical orientation distribution and the orientation separation characteristics, we propose a modified fuzzy C-means cluster algorithm to determine the orientation of each Gabor filter. Since the statistical orientation distribution is based on a set of real palmprint images, the proposed method is more suitable for palmprint recognition. Experimental results indicate that the proposed method achieves higher verification accuracy while compared with that of the original competitive coding scheme and several state-of-the-art methods, such as ordinal measure and RLOC. Considering both the computational complexity and the verification accuracy, competitive code with six orientations would be the optimal choice for palmprint recognition.     

Palmprint verification based on robust line orientation code

In this paper, we propose a novel robust line orientation code for palmprint verification, whose performance is improved by using three strategies. Firstly, a modified finite Radon transform (MFRAT) is proposed, which can extract the orientation feature of palmprint more accurately and solve the problem of sub-sampling better. Secondly, we construct an enlarged training set to solve the problem of large rotations caused by imperfect preprocessing. Finally, a matching algorithm based on pixel-to-area comparison has been designed, which has better fault tolerant ability. The experimental results of verification on Hong Kong Polytechnic University Palmprint Database show that the proposed approach has higher recognition rate and faster processing speed.     

Generating cancelable palmprint templates via coupled nonlinear dynamic filters and multiple orientation palmcodes

A novel scheme for generating cancelable palmprint templates is proposed in this paper. Firstly, a chaotic high speed stream cipher is implemented based on coupled nonlinear dynamic filters (CNDF), in which the CNDF are constructed to have flows inverse to each other. Secondly, renewable and privacy preserving palmprint templates are generated using the CNDF chaotic stream cipher with multiple orientation palmprint features obtained from a bank of Gabor filters and encoded in a phase-coding scheme. Compared with the standard palmprint templates, the cancelable templates have greater ability to discriminate palmprints from different hands by increasing the inter-class divergence of different palms more effectively, while maintaining the intra-class distance among palmprints of the same hands. Lastly, the matching stage is performed directly on the cancelable/encryption domain in parallel to accelerate matching and to protect user’s privacy. Several fusion rules are investigated for the matching scores of different directional PalmCodes to obtain the final matching score. Compared with Max, Min, Median and Product fusion rules, the Sum rule can greatly accelerate the speed and improve the performance Experimental results on the Hong Kong PolyU Palmprint Database verify that the proposed cancelable templates can achieve very high performance and security levels with a very strong ability to reissue palmprint templates. The proposed method can also be implemented at high speed, which satisfies the needs of real-time applications.     

改进的SLTP方法在掌纹识别中的应用

对掌纹识别进行研究,提出了基于改进的软直方图局部三值模式（SLTP）的掌纹识别方法。该方法先对掌纹训练样本进行能量函数的构造,然后用梯度下降法对能量函数进行优化,得到最佳的模糊隶属度函数,进而对掌纹的特征进行提取,最后用Chi概率统计的相似度度量方法进行匹配识别。在PolyU掌纹数据库和IITD掌纹数据库中进行实验验证,结果表明,在相同的训练样本下,改进的SLTP方法相比于SLTP方法,识别率得到提高。从而证明了该方法的有效性。     

Concavity-orientation coding for palmprint recognition

Efficient feature extraction strategies play an important role in palmprint recognition systems. Among various feature extraction methods, orientation methods such as Competitive Code and Half Orientation Code are the baseline ones. They encode responses of a bank of orientational filters into a binary representation and can match a test palmprint sample in real-time with a relatively good accuracy. However, they use the orientation information based upon this idea that palmprints encompass only straight lines with different orientations, whereas in reality, the majority of palm’s lines are curved. This observation naturally brings the idea that the concavity and orientation features as different aspects of palmprints curves might provide more reliable and discriminative representations in palmprint recognition. Motivated by this idea, in this work we investigate the use of the concavity feature in different orientations for palmprint recognition. The experimental results, which are applied on PolyU II, 2D/3D PolyU, and blue and near infrared range images from Multispectral PolyU palmprint databases prove the efficiency of this idea compared to other coding-based methods.     

基于区域特征映射的模糊掌纹识别方法

针对掌纹在非接触采集时易出现模糊现象从而导致系统识别性能降低的问题,建立了区域到点的特征映射模型,提出了一种基于区域特征映射(Region feature map, RFM)的模糊掌纹识别方法.首先根据图像的模糊原理,建立等价的模糊模型,获取模糊掌纹; 然后使用RFM对模糊掌纹进行操作,将高维的区域特征映射到低维的点特征; 最后,采用归一化相关性分类器对掌纹所属类别进行判定识别.使用模糊模型对PolyU掌纹库进行处理得到PolyU模糊掌纹库,并分别在PolyU掌纹库和PolyU模糊掌纹库上进行测试,识别结果较为稳定. 在模糊掌纹库上,本文算法的等错误率(Equal error rate, EER)最小可达0.9069%,优于传统算法,且进行一次识别的时间为33.95ms,得到的特征数据维数较小,降低了算法复杂度,表明了本文算法的有效性和实时性.     

基于Nonsubsampled Contourlet变换的掌纹特征提取算法

为了研究Nonsubsampled Contourlet变换(NSCT)在掌纹识别应用方面的可行性和性能,本文采用MATLAB仿真手段,利用NSCT对纹理特有的各向异性和多尺度特点,以香港理工大学采集的掌纹图像为研究样本,建立掌纹识别的分析和研究平台,针对NSCT从掌纹图像中分解得到的多个系数矩阵,研究掌纹特征的提取算法。实验结果表明,NSCT在掌纹识别方面具有较好的性能和较高的识别率,从而验证了该方法在掌纹识别中的有效性和识别效果。     

Robust palmprint identification based on directional representations and compressed sensing

In this paper, we propose a novel approach for palmprint recognition, which contains two interesting components: directional representation and compressed sensing. Gabor wavelets can be well represented for biometric image for their similar characteristics to human visual system. However, these Gabor-based algorithms are not robust for image recognition under non-uniform illumination and suffer from the heavy computational burden. To improve the recognition performance under the low quality conditions with a fast operation speed, we propose novel palmprint recognition approach using directional representations. Firstly, the directional representation for palmprint appearance is obtained by the anisotropy filter, which is robust to drastic illumination changes and preserves important discriminative information. Then, the principal component analysis (PCA) is used for feature extraction to reduce the dimensions of the palmprint images. At last, based on a sparse representation on PCA feature, the compressed sensing is used to distinguish palms from different hands. Experimental results on the PolyU palmprint database show the proposed algorithm have better performance than that of the Gabor based methods.     

Score level fusion of voting strategy of geometric hashing and SURF for an efficient palmprint-based identification

This paper proposes an efficient indexing scheme for palmprint-based identification system. The proposed system uses geometric hashing of SURF key-points to index the palmprint into hash table and makes score level fusion of voting strategy based on geometric hashing and SURF score to identify the live palmprint. All ordered pairs of SURF key-points of the palmprint are scaled and mapped to a predefined coordinate system and all other points are similarity transformed. The new location after transformation serves as the index of the hash table. During identification, all ordered pairs of key-points of live palmprint are scaled and mapped to the coordinate system while remaining points are similarity transformed. A vote is casted to all images in the corresponding bins. Images having votes more than certain threshold are considered as candidate images of the live palmprint. SURF features of the live palmprint and the candidate images are compared for matching. Matching scores which are based on SURF key-points and vote of the corresponding candidate image are fused using weighted sum rule. The candidate image with the highest fused score is considered as the best match. The system is tested on IITK, CASIA and PolyU datasets. It has been observed that penetration rate of the proposed system is less than 30% for 0% bin miss rate (BMR) and has the identification accuracy of more than 97% for all three datasets. Further, the system is evaluated for robustness on downscaled and rotated. It has been found that the identification accuracy of the system for top best match is more than 90% for images downscaled up to 49% and accuracy is more than 85% when images are rotated at any angle.     

基于水平扩张毯子维的掌纹识别

掌纹识别作为一种新兴的生物识别技术近年来得到了广泛研究.鉴于毯子 维(Blanket dimension, BD)的多分辨率特性和掌纹纹理的方向性,本文对比分析了普通毯子维、水平方向扩张 毯子维和垂直方向扩张毯子维对掌纹分形特征的表达性能,提出并研究了一种基于水平扩张 毯子维的掌纹识别新算法.本文算法在香港理工大学掌纹数据库(版本2)进行了实验,实验结 果表明,水平扩张毯子维可以很好地提取掌纹特征,获得的识别率可达99.9%,识别时间 小于287ms,可满足在线掌纹识别.     

融合水平梯度与局部信息强度的掌纹识别算法

掌纹纹线特征是掌纹最有效的特征.由于在采集掌纹时不可避免地会产生尺度不一致、细微的旋转或平移等问题,使得准确地提取以及描述纹线特征成为掌纹识别的一大难点.针对这一问题,提出了一种融合水平梯度与局部信息强度的掌纹识别算法(Horizontal Gradient-Local Information Intensity,HG-LII).首先,使用不同的均值滤波模板消除细小、不规则、不稳定的掌纹纹线特征,对处理后的图像使用水平梯度算子得到水平方向的梯度图像,并进行二值化;其次使用分块思想计算掌纹纹线的信息强度,并将其作为特征向量;最后采用卡方距离进行匹配,判断掌纹所属类别.在PolyU掌纹库上的实验结果表明,该算法识别率达到99.89％,与传统的提取纹线算法相比,识别率有明显的提高,表明了该算法的有效性.     

Designing efficient fusion schemes for multimodal biometric systems using face and palmprint

In this paper, we address the problem of designing efficient fusion schemes of complementary biometric modalities such as face and palmprint, which are effectively coded using Log-Gabor transformations, resulting in high dimensional feature spaces. We propose different fusion schemes at match score level and feature level, which we compare on a database of 250 virtual people built from the face FRGC and the palmprint PolyU databases. Moreover, in order to reduce the complexity of the fusion scheme, we implement a particle swarm optimization (PSO) procedure which allows the number of features (identifying a dominant subspace of the large dimension feature space) to be significantly reduced while keeping the same level of performance. Results in both closed identification and verification rates show a significant improvement of 6% in performance when performing feature fusion in Log-Gabor space over the more common optimized match score level fusion method.     

一种改进的BDPCA掌纹识别方法

在小样本的情况下,BDPCA算法中采用以训练样本的平均值作为样本分布中心,所得的特征值不一定是最优的。为此,提出了一种基于样本散度矩阵的改进BDPCA掌纹识别算法。该算法采用训练样本的K值矩阵替代训练样本的均值矩阵,构建相应的总体散度矩阵。在PolyU和CASIA掌纹库上的实验结果证明,该方法的最优识别率高于传统的BDPCA算法。     

基于GIDBC的掌纹识别算法研究

针对采用分形维数作为特征描述掌纹信息不准确的问题,对差分盒子维进行改进提高特征区分性.此外,由于采用单一的特征不足以描述掌纹纹理,引入Gabor变换,提出一种基于Gabor变换与改进差分盒子维(GIDBC,Gabor improved differential box counting)相结合的掌纹识别算法.通过在PolyU掌纹图像库上实验,与传统高性能算法比较,本算法识别率最高可达到99.78％,表明了本文方法的有效性,同时特征提取与匹配时间为338 ms,满足实时性要求.     

基于大尺度方向场描述子的指纹分类算法

指纹分类通过将指纹划分到一系列预定义的类别之中以极大降低指纹匹配的工作量,是指纹识别系统中一项非常关键的技术。受FingerCode分类特征启发,提出了一种称为大尺度方向场描述子的新的分类特征,该特征以指纹核心点(core点)为中心构造大尺度环形网状结构,通过抽取网状结构中节点处的方向来形成特征向量,以达到近似描述核心点周围的方向模式的目的。大量实验结果表明:相较于FingerCode特征,新特征在保证分类准确率的同时,由于特征提取方式更为简单、高效,分类速度也提高了近20倍。     

二维EMD分解提高PCA掌纹识别率

为了提高常用于在线掌纹识别的PCA方法的识别率,提出融合BEMD技术的PCA掌纹识别方法.二维EMD技术能够在频率域内实现图像的多层分解,在不同频段内对图像进行处理.掌纹图像的低频部分容易受到背景等因素的影响,所以实验中提取、利用掌纹高频信息,去除低频信息,充分利用掌纹中的个人特征信息,抑制干扰,提高识别率.基于香港理工大学掌纹数据库的仿真结果显示,这种方法的识别率远高于传统PCA方法,体现了一定的理论研究意义和实用价值.     

2D and 3D palmprint fusion and recognition using PCA plus TPTSR method

This paper employs both two-dimensional (2D) and three-dimensional (3D) features of palmprint for recognition. While 2D palmprint image contains plenty of texture information, 3D palmprint image contains the depth information of the palm surface. Using two different features, we can achieve higher recognition accuracy than using only one of them. In addition, we can improve the robustness. To recognize palmprints, we use two-phase test sample representation (TPTSR) which is proved to be successful in face recognition. Before TPTSR, we perform principal component analysis to extract global features from the 2D and 3D palmprint images. We make decision based on the fusion of 2D and 3D features matching scores. We perform experiments on the PolyU 2D + 3D palmprint database which contains 8,000 samples and achieve satisfying recognition performance.