Abstract:
A method of iris recognition using a cumulative-sum-based change point analysis and an apparatus using the same are disclosed. The method includes: transforming an iris image to a polar coordinated image having n×m pixel size and dividing the polar coordinated image into at least one cell; grouping the divided iris images into at least one of first groups having a predetermined number of cells, and at least one of second groups each having more cells than the first group has; performing a cumulative-sum-based change point analysis using a predetermined characteristic pattern value of each cell as a representative value; and generating a pattern vector by assigning a predetermined value to a cell having the change point and assigning a different value to other cells.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
   This application claims the benefit of Korean Patent Application No. 10-2005-0118628, filed on Dec. 7, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method of iris recognition to identify an authorized user and an apparatus using the same, and more particularly, to a method of iris recognition to identify an authorized user through simply and effectively extracting characteristics of iris using a cumulative-sum-based change point analysis (CPA) with less amount of calculation. 
   2. Description of the Related Art 
   Many methods of extracting characteristic patterns from iris were introduced. Among them, a Garbor transform and a wavelet method are widely known technologies to analyze the characteristic patterns of iris. Daugman introduced a conventional method of extracting characteristic patterns from iris using the Garbor transform and creating a pattern vector. Such a Daugman&#39;s method requires high quality iris image. Therefore, Daugman&#39;s method requires very expensive image processing equipment. Also, the computation complexity thereof is very high due to the calculations related to exponential functions and numerous multiplications. Furthermore, the obtained iris image is transformed into a polar coordinated image and the characteristic patterns are extracted from the polar coordinated image. In this procedure, some differences are generated between the obtained iris image and the polar coordinated image due to the position of iris is shifted. Therefore, the performance of iris recognition obtained through extracting and matching iris patterns is degraded. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method of iris recognition to identify an authorized user through extracting characteristic patterns from iris using a cumulative-sum-based change point analysis (CPA), which is simple and effective while requiring less amount of computation compared to a conventional method. 
   According to an aspect of the present invention, there is provided a method of iris recognition using cumulative sum based change analysis including: transforming an iris image to a polar coordinated image having n×m pixel size and dividing the polar coordinated image into at least one cell; grouping the divided iris images into at least one of first groups having a predetermined number of cells, and at least one of second groups each having more cells than the first group has; performing a cumulative-sum-based change point analysis using a predetermined characteristic pattern value of each cell as a representative value; and generating a pattern vector by assigning a predetermined value to a cell being the change point and assigning a different value to other cells. 
   According to another aspect of the present invention, there is provided an apparatus for iris recognition using a cumulative-sum-based change point analysis including: a dividing unit for transforming an iris image to a polar coordinated image having n×m pixel size and dividing the polar coordinated image into at least one cell; a grouping unit for grouping the divided iris images into at least one of first groups having a predetermined number of cells, and at least one of second groups each having more cells than the first group has; a pattern vector generating unit for generating a pattern vector by assigning a predetermined value to a cell being the change point and assigning a different value to other cells after performing a cumulative-sum-based change point analysis using a predetermined characteristic pattern value of each cell as a representative-value; and an authentication unit for performing an authentication process by receiving the pattern vector generated from the pattern vector generating unit and a previously registered pattern vector. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1A  shows sample data for the cumulative sum based CPA; 
       FIG. 1B  is a flowchart of the cumulative sum based CPA; 
       FIG. 1C  shows equations of calculating an accumulative sum for the cumulative sum based CPA of  FIG. 1B  using sample data shown in  FIG. 1A ; 
       FIG. 1D  is a graph showing the result of the equations shown in  FIG. 1C ; 
       FIG. 2  is a flowchart of a method of iris recognition using a cumulative sum based CPA according to an embodiment of the present invention; 
       FIG. 3  is a block diagram of an apparatus for iris recognition using a cumulative sum based CPA according to an embodiment of the present invention; 
       FIG. 4  is a view showing dividing of iris image into basic cell regions; 
       FIG. 5  is a view showing grouping of cell regions for the CPA after dividing the iris image into basic cell regions; 
       FIG. 6A  is a graph showing average grey values of 6 cell regions; and 
       FIG. 6B  is a graph showing results of cumulative sum based CPA based on the graph in  FIG. 6A . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
   Hereinafter, a cumulative-sum-based change point analysis (CPA) will be described with reference to  FIGS. 1A and 1D  at first.  FIG. 1A  shows sample data for the cumulative sum based CPA, and  FIG. 1B  is a flowchart of the cumulative sum based CPA.  FIG. 1C  shows equations of calculating a cumulative sum for the cumulative sum based CPA of  FIG. 1B  using sample data shown in  FIG. 1A , and  FIG. 1D  is a graph showing the result of the equations shown in  FIG. 1C .  FIG. 1A  shows trade deficits  110  of each month in 1987 and 1988 as sample data to describe the cumulative sum based CPA. That is, the cumulative sum based CPA finds a region having a sharpest change point among arranged sample data. Now, a method of calculating a cumulative sum with each input data will be described. At first, an average value (  X ) of input data is calculated in operation S 120 . Based on the calculated average value, a difference between a current input data and the average value (  X ) is calculated. The cumulative sum based CPA is not a method of calculating a difference between input data. It calculates difference between the input data and the average value. Therefore, a variation ratio of input data can be observed throughout the entire input data. In order to calculate the difference between the average and the input data, a cumulative sum at 0 (S 0 =0) is calculated, and then other cumulative sums (S i ) are calculated by adding a current value to difference between the current value and the average of previous cumulative sum. In the present example, i is 1 to 24.  FIG. 1C  shows cumulative sums calculated by applying sample data shown in  FIG. 1A . The graph shown in  FIG. 1D  is created based on the cumulative sums shown in  FIG. 1C . As shown in the graph  150  in  FIG. 1D , a numeral reference  151  denotes a sharpest change point of input data. That is, the change point  151  of the November 1987 is a sharpest charge point among input data. The left side curve of the change point  151  has an upward slope. That is, the input values are generally larger than the average value in the left side curve of the change point  151 . The right side curve of the change point  151  has a downward slope. That is, the input values are generally smaller than the average value in the right side curve of the change point  151 . And, the cumulative sums begin from 0 and end at 0. 
   A method of iris recognition using a cumulative-sum-based change point analysis (CPA) according to an embodiment of the present invention will be described with reference to  FIGS. 2 through 7 .  FIG. 2  is a flowchart of a method of iris recognition using a cumulative sum based CPA according to an embodiment of the present invention, and  FIG. 3  is a block diagram of an apparatus for iris recognition using a cumulative sum based CPA according to an embodiment of the present invention.  FIG. 4  is a view showing dividing of an iris region into basic cell regions, and  FIG. 5  is a view showing grouping of cell regions for the CPA after dividing the iris region into basic cell regions.  FIG. 6A  is a graph showing average grey values of 6 cell regions, and  FIG. 6B  is a graph showing results of cumulative sum based CPA based on the graph in  FIG. 6A . 
   A dividing unit  310  transforms an iris image to polar coordinates and divides the transformed iris region into basic cell regions for the cumulative-sum-based change point analysis. That is, the image transformed to the polar coordinate of iris is divided by a cell region as a basic unit region. At first, an obtained iris image is transformed into the polar coordinated iris image for analysis. The polar coordinated iris image has a pixel size of 64×512. The characteristic patterns of iris are well shown in an autonomic nerve, and there is no need to analyze entire characteristic patterns of iris image. About 78% of iris image in vertical direction is sufficient to extract characteristic patterns of iris from the polar coordinate image  410 . That is, a portion of iris image below than a dotted line is not used to extract the characteristic pattern of iris. That is, about 50 pixels in a vertical direction are used, which is calculated by 64×0.78=50 pixels. As shown in  FIG. 4 , the basic cell region  420  is configured of 5×3 pixels. That is, one cell region is a 5×3 pixel size, and an average grey value is used as a representative value of a basic cell region to calculate the cumulative sum. There are 170 basic cell regions included in the horizontal line of the iris image because the horizontal pixel size of iris image is 512 and the horizontal pixel size of the basic cell region is 3 (512÷3=170). There are 10 basic cell regions  430  included in the vertical line of the iris image because the vertical pixel size of the iris image is 50 and the vertical pixel size of the basic cell region is 5 (50÷5=10). Therefore, the number of basic cell regions in the iris image is 1700 which is calculated from 170×10. That is, the iris image is divided into 170 basic cell regions in operation S 210 . 
   A grouping unit  320  groups the basic cell regions into a semi local group or a local group after dividing the transformed iris image as shown in  FIG. 3  into the basic cell regions, where the semi local group is described as a first group in claims and the local group is described as a second group. That is, the basic cell regions are grouped in a horizontal direction as shown in  510  and  520  of  FIG. 5 . As shown in  530  of  FIG. 5 , there are 170 cell regions in one horizontal line and there are 10 horizontal lines in the iris image. As shown in  510  of  FIG. 5 , cell regions  1  to  5  are grouped as a first group in operation S 220 . A pattern vector generating unit  330  finds a cell region that has a sharp change point by applying the cumulative sum based on a change point analysis (CPA) algorithm within this group. The pattern vector generating unit  350  also finds a sharp change point in a second group  520  using the same method. The pattern vector generating unit  350  finds the sharp change point more accurately by overlapping the groups with adjacent groups as shown in  520  of  FIG. 5  in operation S 230 . One horizontal line  530  is divided into two groups  510  and  520 . Therefore, each line creates  170  pattern vectors as like as  550  and  560  of  FIG. 5 . A cell region selected as the sharp charge point is set as 1, and other cell regions are set as 0 to create the pattern vectors. Therefore, the pattern vector of 3400 bits ((170+170)×10) is generated in operation S 240 . An authenticating unit  340  determines whether a currently inputted iris characteristics pattern is matched with registered iris characteristics patterns of authenticated person through calculating a similarity using a hamming distance between the calculated pattern vector and the registered pattern vector and using the statistical method based on a predetermined threshold value in operation S 250 . The pattern vector may be extracted through grouping the basic cell regions in the vertical direction as like as the pattern vector extracting in the horizontal directions. 
     FIGS. 6A and 6B  show the cumulative-sum-based change point analysis using a branch as an average grey value of cell regions.  FIGS. 6A and 6B  also show a method of generating a pattern vector for preventing the performance of iris recognition from being degraded according to the shift of the iris image.  FIG. 6A  is a graph showing grey values of 6 cell regions, and  FIG. 6B  is a graph obtained by calculating cumulative sums using 6 cell regions as one group. In these graphs, a change point  620  has a largest absolute value of cumulative sum S 4  in the cell region. Therefore, the fourth cell region is the sharp change point. In order to prevent the performance of iris recognition from being degraded according to the iris image shift, the cell regions of left side curve from the charge point  620  which have downward slope are set as 0, and the cell regions of right side curve from the change point  620  which have upward slope are set as 1. Accordingly, the similarity of the extracted pattern vectors can be maintained much longer although the shape change point is changed according to the movement of iris image because the overlapping portion for general grey value variation is maintained much longer. 
   The method of iris recognition using cumulative sum based CPA according to the present invention can also be embodied as computer-readable codes on a computer-readable recording medium. The computer-readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer-readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, and optical data storage devices. The computer-readable recording medium can also be distributed over network coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. 
   As described above, the method of iris recognition using cumulative sum based CPA and the apparatus using the same according to the present invention simply and effectively recognizes the iris without requiring mass amount of calculation compared to the conventional method using wavelet transforming based pattern extraction. 
   Also, the present invention stably recognizes the iris by generating the pattern vector using the extracted characteristic patterns of iris for preventing the performance from being degrade according to the movement of the iris image. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.