Study On Some Key Issues Of Iris Recognition

Iris recognition is a kind of novel biometrics which was developed from 1990s and it has attracted more and more attention because of its high accuracy.Thanks to its complex structures and abundant features,the iris has many desirable properties,such as unique, stable,collectable,hard to be changed,non-intrusive,and so on.The property of non-intrusive is bound to be the trend of biometrics development.In this thesis,through the analyses of the condition when eye images are captured by the system of iris recognition,some problems contained by eye images used for iris recognition are discussed.In order to resolve these problems,several methods of image preprocessing,feature extracting and matching are researched.Eye images used for experiments come from CASIA-IrisV3-Interval database.Main works and results of this thesis are as follows.(1) Aiming at the problems of iris translation,irrelative regions,and reflected faculaea, method of iris localization based on gray-value distributing characteristics of eye images is proposed.It firstly detects a point in the pupil according to gray-value distribution features of pupil.And it respectively detects three boundary points in the inner and outer boundaries according to the higher gradients of iris boundaries.Then using these six boundary points,it determines the centres and radiuses of inner and outer boundaries according to the principle that a circle can be fixed by three points which are not in the same line.Experimental results demonstrate that the proposed method can effectively resolve all above three problems.The successful localization probability is 96.12%and the average localization time is 127ms.Compared with classical methods,the proposed method has higher successful localization probability but it need fewer localization time.(2) Aiming at the problems of iris flexing and disturbances of eyelashes and eyelids,the iris is normalized to an iris image having the resolution of 512×64 using the transform from Cartesian coordinates to polar coordinates.Then an effective iris region with the size of 256×32 is determined and this region contains pure iris veins without any disturbance. (3) Aiming at the problem that the effective iris region is incomplete,four methods of feature extracting and matching are proposed.Firstly,a method of iris matching based on the similarity of gray-value surfaces is proposed.It represents the effective iris region using a three-dimensional gray-value surface and then it directly achieve iris matching according to the similarity of two gray-value surfaces.Secondly,an iris block-encoding method based on statistic of local information is proposed.It extracts two kinds of comparable relations as distinguishable features to accomplish iris encoding and matching.One is the relation between local and global information,and anther is the relation between neighbor local information.Thirdly,a method of feature extracting and matching based on structural features is proposed.It extracts the position feature of iris veins and it encodes this kind of feature into a binary iris code.Then it achieves iris matching using the Hamming distance.Finally,a method of feature extracting and matching based on weighted mean phase vector of phase congruency is proposed.For each point in the image,the proposed method represents their weighted mean phase vector on the maximal responding orientation of phase congruency into a binary iris code.And then it still accomplishes iris matching using the Hamming distance.In addition,in order to objectively evaluate the accuracy of each method,above four methods are compared with the classical method based on Gabor transform.Experimental results demonstrate that,for these four methods,the method based on weighted mean phase vector of phase congruency has the highest accuracy.Its correct recognition rate is 98.94%.Compared with classical method,its correct recognition rate increased for about 10.63%.Thus,if this method serves as the core module of iris recognition and combines with the method of image preprocessing,an iris recognition method having high accuracy will be obtained.(4) Aiming at the problem of iris rotation,a method of translated matching for several times is proposed in the procedure of researching the method of iris matching based on the similarity of gray-value surfaces.Experimental results demonstrate that,if the translated matching is accomplished for 12 times,the problem of iris rotation can be resolved effectively when the resolution of iris image is 512×64.In fact,the method based on the similarity of gray-value surfaces is a kind of application of image registration,so this conclusion has importantly instructional significance to other methods of feature extracting and matching for the same database.