一种改进的虹膜图像分割算法

如何迅速、准确地分割虹膜区域是基于虹膜图像的身份鉴别技术的一个研究热点和难点。本文结合虹膜图像的特点，在内边缘的定位中采用了阈值化结合最小二乘估计的方法；对外边缘和眼睑的边缘图进行预处理，并改进了Hough变换的决策方法，准确而快速地分割出虹膜区域。     

Efficient iris segmentation method in unconstrained environments

Recently, iris recognition systems have gained increased attention especially in non-cooperative environments. One of the crucial steps in the iris recognition system is the iris segmentation because it significantly affects the accuracy of the feature extraction and iris matching steps. Traditional iris segmentation methods provide excellent results when iris images are captured using near infrared cameras under ideal imaging conditions, but the accuracy of these algorithms significantly decreases when the iris images are taken in visible wavelength under non-ideal imaging conditions. In this paper, a new algorithm is proposed to segments iris images captured in visible wavelength under unconstrained environments. The proposed algorithm reduces the error percentage even in the presence of types of noise include iris obstructions and specular reflection. The proposed algorithm starts with determining the expected region of the iris using the K-means clustering algorithm. The Circular Hough Transform (CHT) is then employed in order to estimate the iris radius and center. A new efficient algorithm is developed to detect and isolate the upper eyelids. Finally, the non-iris regions are removed. Results of applying the proposed algorithm on UBIRIS iris image databases demonstrate that it improves the segmentation accuracy and time.     

Developing Iris Recognition System for Smartphone Security

Smartphones have become an important way to store sensitive information; therefore, users’ privacy needs to be highly protected. This can be done by using the most reliable and accurate biometric identification system available today: iris recognition. This paper develops and tests an iris recognition system for smartphones. The system uses eye images that rely on visible wavelength; these images are acquired by the smartphone built-in camera. The development of the system passes through four main phases: the first phase is the iris segmentation phase, which is done in three steps to detect the iris region from the captured image, which contains the eye and part of the face using Haar Cascade Classifier training, pupil localization, and iris localization using a Circular Hough Transform. In the second phase, the system applies normalization using a Rubber Sheet model, which converts the iris image to a fixed size pattern. In the third phase, unique features are extracted from that pattern using a Deep Sparse Filtering algorithm. Finally, in the matching phase, seven different matching techniques are investigated to decide the most appropriate one the system will use to verify the user. Two types of testing are conducted: Offline and Online tests. The BIPLab database and a collected dataset are used to measure the accuracy of the system phases and to calculate the Equal Error Rate (EER) for the whole system. The average EER is 0.18 for the BIPLab database and 0.26 for the collected dataset.     

A new segmentation approach for iris recognition based on hand-held capture device

Iris segmentation is an important step for automatic iris recognition. This paper presents a new iris segmentation method for hand-held capture device. We use a geometrical method for pupil detection. The bottom point of pupil is used as the reference point for pupil localization because it is insensitive to pupil dilation and not affected by the top eyelid or eyelashes. To decrease computational cost, the outer (or limbus) boundary of iris is localized based on shrunk image using Hough transform and modified Canny edge detector. The lower part of iris pattern is used for recognition in order to reduce the occlusion by eyelashes and eyelids. Experimental results demonstrate that the proposed method has an encouraging performance.     

基于深度反卷积网络的虹膜定位方法研究

精确而快速地进行虹膜定位是有效地进行虹膜识别的重要前提.传统的虹膜定位方法有Daugman定位法、Hough变换定位法等,但其对睫毛比较浓密、虹膜被遮挡较多等情况下的图片处理效果不是很好.文章在总结前人工作的基础上,实现了一套基于深度学习的虹膜定位系统.该系统利用深度学习方法,根据虹膜图像区域的特点,对图像进行像素级分类.根据像素分类结果,可以很好地标识虹膜区域和非虹膜区域,达到定位识别虹膜区域的目的,并在中国科学院自动化所公布的虹膜数据集CASIA-IrisV3-Interval上验证了文章工作的有效性,像素分类精度达到约98.4％,达到了较高的鲁棒性.     

基于最小二乘修正的随机Hough变换直线检测

利用Hough变换进行直线检测时,由于直线在参数空间中的映射容易受到邻近目标、噪声以及本身非理想状态的干扰,算法中的投票过程较易出现无效累积,进而导致虚检、漏检及端点定位不准等问题.针对传统方法的上述缺陷,提出了一种基于 ρ-θ 域最小二乘拟合修正的随机Hough变换的直线检测方法.首先, 在随机抽样时利用像素-长度比值对抽样的有效性进行判定,剔除不在直线上的抽样点对;然后, 对邻域相关点进行 ρ-θ 域的最小二乘拟合,得到修正后的直线参数用于累加投票,投票过程中设定累加阈值,通过检测峰值点逐次检出疑似长直线;最后, 通过设定断裂阈值对每条长直线进行筛选和分段,定位出直线段的端点.仿真实验表明,所提方法在投票时有效抑制了复杂环境对局部最大值的干扰,使直线检测的准确率得到显著提升.     

Robust and accurate iris segmentation in very noisy iris images

Iris segmentation plays an important role in an accurate iris recognition system. In less constrained environments where iris images are captured at-a-distance and on-the-move, iris segmentation becomes much more difficult due to the effects of significant variation of eye position and size, eyebrows, eyelashes, glasses and contact lenses, and hair, together with illumination changes and varying focus condition. This paper contributes to robust and accurate iris segmentation in very noisy images. Our main contributions are as follows: (1) we propose a limbic boundary localization algorithm that combines K-Means clustering based on the gray-level co-occurrence histogram and an improved Hough transform, and, in possible failures, a complementary method that uses skin information; the best localization between this and the former is selected. (2) An upper eyelid detection approach is presented, which combines a parabolic integro-differential operator and a RANSAC (RANdom SAmple Consensus)-like technique that utilizes edgels detected by a one-dimensional edge detector. (3) A segmentation approach is presented that exploits various techniques and different image information, following the idea of focus of attention, which progressively detects the eye, localizes the limbic and then pupillary boundaries, locates the eyelids and removes the specular highlight.     

结构化道路上应用区域划分的车道线识别

针对多数研究中车道线检测的准确性和实时性难以有效平衡的问题,提出了一种应用区域划分的车道线识别方法。首先通过改进的大津(OTSU)算法提取边缘图像,再在所得边缘图像的基础上,利用改进的概率霍夫变换(PPHT)提取车道标识线上的特征点,并采用最小二乘法(LSM)对特征点点集进行直线拟合,最后通过提出的路面干扰线规避算法检测所有拟合得到的直线段并筛选可能的车道线。在实验方面,引入三种算法作为对比,并利用提出的准确性评价模型对500幅典型道路场景图中的车道线识别结果进行评估,同时统计在处理一段长为1 min 26 s的道路视频时每帧图像序列的平均耗时。实验结果表明所提算法的查准率、查全率、F量测值均优于对比算法,且达到实时处理的要求。     

IrisCodeNet：虹膜特征编码网络

使用有效的特征提取算法对虹膜纹理进行准确的表达是虹膜识别技术的关键。基于虹膜识别任务的特殊性,提出了用于虹膜特征编码的网络模型IrisCodeNet。该网络架构使用了改进的BasicBlock,并结合了可以扩大决策边界的损失函数AM-Softmax（additive margin softmax）。为了获取最佳的虹膜识别效果,对AM-Softmax的参数设置、虹膜图像预处理输入形式、数据增强方式、网络输入尺寸做了细致的研究。实验结果表明：使用IrisCodeNet训练得到的特征提取器在CASIA-Iris-Thousand、CASIA-Iris-Distance、IITD虹膜数据库上进行测试,所评估的等错误率（equal error rate,EER）和正确接受率（true acceptance rate,TAR）均远远超过了广泛应用的传统算法。特别地,IrisCodeNet无需传统的虹膜归一化或精确的虹膜分割步骤依然取得了极好的识别效果。并且使用Grad-CAM（gradient-weighted class activation mapping）算法进行了可视化分析,结果表明该网络框架有效地关注了虹膜纹理信息,从而证明了IrisCodeNet具有较强的虹膜纹理特征提取能力。     

基于生物形状知识的人眼定位方法

准确地定位出人眼位置并分离出虹膜、眼睑等区域对虹膜识别、人脸识别等生物特征识别技术具有重要意义.但是,在非理想环境下,人眼图像分辨率通常较低,并且容易受到光照条件、睫毛、阴影等噪声影响,对人眼区域进行正确分割是一项非常具有挑战性的工作.因此,本文针对姿态幅度较小的无遮挡人眼图像分割存在的一些问题,利用Hough圆变换和形态学算法改进低分辨率下人眼的定位.该方法首先利用现有的人脸对齐方法分割出人眼感兴趣区域,采用双线性插值法对人眼图像进行预处理,去除镜面反射光斑;然后根据人眼图像中各区域的灰度分布规律,利用带约束的Hough圆检测算法定位出虹膜;之后结合全局动态阈值、局部自适应阈值及形态学算法分别定位出人眼上下眼睑,并利用最小二乘法拟合上下眼睑,最终分割出人眼虹膜、上下眼睑、巩膜等区域;最后在UBIRIS v1.0数据库及低分辨率人脸图像上对本文提出的算法进行测试.实验结果表明,本文提出的方法对实验室环境下高清虹膜图像及低分辨率人脸图像上的人眼定位均具有较强的鲁棒性.     

多算法融合虹膜识别中的规范化模型比较研究

虹膜识别易受环境影响,利用多算法融合识别提高复杂应用环境下虹膜识别可靠性是一种非常有效的途径。本文针对多算法融合虹膜识别中的关键步骤——规范化模型选择做了比较性研究。首先搭建多算法融合虹膜识别平台,对常见的三种规范化模型在UBIRIS虹膜库中做了比较测试,实验结果证明双sigmoid函数指数模型性能最优。本文研究可对多算法融合的研究提供理论参考。     

A universal texture segmentation and representation scheme based on ant colony optimization for iris image processing

This paper proposes a novel scheme for texture segmentation and representation based on Ant Colony Optimization (ACO). Texture segmentation and texture characteristic expression are two important areas in image pattern recognition. Nevertheless, until now, how to find an effective way for accomplishing these tasks is still a major challenge in practical applications such as iris image processing. We propose a framework for ACO based image processing methods. Considering the specific characteristics of various tasks, such a framework possesses the flexibility of only defining different criteria for ant behavior correspondingly. By defining different kinds of direction probability and movement difficulty for artificial ants, an ACO based image segmentation algorithm and a texture representation method are then presented for automatic iris image processing. Experimental results demonstrated that the ACO based image processing methods are competitive and quite promising, with excellent effectiveness and practicability especially for images with complex local texture situations.     

Houhg变换OCR图象倾斜矫正方法

在光学字符识别（OCR）图象扫描输入的过程中,扫描图象或多或少会出现某种程度的倾斜,这种图象的倾斜不仅会给下一步字符的切割造成困难,也影响最终的字符识别精度,通常情况下,为避免用户重新扫描,可以通过软件方法对图象进行矫正,为此提出一种利用Hough变换进行图象倾斜矫正的方法,为克服Hough变换计算量大的缺点,该方法采用了变分辨率图象金字塔策略,实验结果表明,该方法能快速准确测量出扫描图象的倾斜角度,并且具有很高的抗噪声性和应用适应性。     

结合形态学的Hough变换虹膜定位改进算法

虹膜定位是在虹膜图像中确定虹膜的内外边界,是虹膜识别过程的首要环节。Hough变换是虹膜定位的经典算法,但对原始图像质量要求高,算法运算时间长。依据人眼图像的灰度特性,结合形态学处理提出一种改进的Hough变换定位新算法。对图像进行灰度二值化运算后进行形态学处理分离出瞳孔,结合Sobel算子边缘检测出瞳孔边界点,通过最小二乘法拟合定位出虹膜内边界;在先验知识和形态学处理的基础上对图像进行Hough变换,定位出虹膜的外边界。实验表明所提出的算法性能比传统Hough变换有较大提高,可用于实际虹膜识别的预处理过程中。     

The modified adaptive Hough transform (MAHT)

A fast and robust algorithm for extracting line segments from an image through use of the Hough Transform is presented. The framework for our algorithm comes from the work of Illingworth and Kittler. We have extended their Adaptive Hough Transform algorithm to handle lines of arbitrary slope, multiple lines, and lines in very low signal to noise environments. We present our Modified Adaptive Hough Transform along with experimental results obtained with data from a tactile sensor.     

Selection of parameters in iris recognition system

This paper presents the detailed analysis of implementation issues occurred during preparation of the novel iris recognition system. First, we shortly describe the currently available acquisition systems and databases of iris images, which were used for our tests. Next, we concentrate on the feature extraction and coding with the execution time analysis. Results of the average execution time of loading the image, segmentation, normalization, and feature encoding, are presented. Finally, DET plots illustrate the recognition accuracy for IrisBath database.     

自然环境下水果图像分割与定位研究

研究了自然环境下苹果、梨、桃子、杏子、李子、石榴、枣、樱桃等水果图像的果实和背景颜色特征，提出了用2r-g-b分量进行图像分割的方法。为了使Hough变换能够检测出水果果实，该文对随机圆Hough变换算法进行了改进，增加了检测圆的梯度约束和半径约束。试验表明对多数水果的图像利用2r-g-b进行分割，并用二值形态学方法对图像进行滤波后，用随机圆Hough变换可以有效地检测出了水果果实。     

虹膜内外边缘的快速定位算法

虹膜定位是虹膜识别过程中的重要环节,定位的速度和精度决定了整个虹膜识别系统的性能。论文提出一种基于Hough变换的虹膜定位算法,根据虹膜图像特点,先对其进行预处理,再用灰度投影法粗定瞳孔圆心;通过对虹膜内外边缘的“先采样后变换”,减少Hough变换的运算量;利用虹膜内外边缘之间的耦合关系,由内至外精确地确定出边缘。对300多幅虹膜样本的处理结果表明,此算法快速、精确、鲁棒。