Personal authentication method, personal authentication apparatus and image capturing device Number:7,155,035 from the United States Patent and Trademark Office (PTO) owispatent

Title: Personal authentication method, personal authentication apparatus and image capturing device

Abstract: A plurality of iris images of a person to be authenticated in which the positions of extraneous light reflection are respectively different are captured by using an image capturing device. Iris codes, that is, features for authentication, are respectively extracted from the plural iris images, and the plural iris codes thus extracted are respectively compared with a registered iris code, so as to generate a plurality of comparison results. The plural comparison results are integrated to obtain an ultimate comparison score, which is used for the authentication.

Patent Number: 7,155,035 Issued on 12/26/2006 to Kondo,   et al.

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Inventors:	Kondo; Kenji (Kyoto, JP), Azuma; Takeo (Nara, JP), Uomori; Kenya (Osaka, JP), Aoki; Yoshito (Kanagawa, JP)
Assignee:	Matsushita Electric Industrial Co., Ltd. (Osaka, JP)
Appl. No.:	10/358,967
Filed:	February 5, 2003

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Foreign Application Priority Data

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May 02, 2002 [JP]			2002-028446

Current U.S. Class:	382/117 ; 340/5.52; 340/5.53; 713/186; 902/3
Current International Class:	G06K 9/00 (20060101); G05B 19/00 (20060101); H04K 1/00 (20060101)
Field of Search:	382/115-127 713/186 902/3 340/5.52,5.53

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References Cited [Referenced By]

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Foreign Patent Documents

	1 041 522		Oct., 2000		EP
	1 139 301		Oct., 2001		EP
	09-161135		Jun., 1997		JP
	09-212644		Aug., 1997		JP
	10-005195		Jan., 1998		JP
	10-021392		Jan., 1998		JP
	10-162146		Jun., 1998		JP
	10-162416		Jun., 1998		JP
	11-203478		Jul., 1999		JP
	2000-060825		Feb., 2000		JP
	2000-132686		May., 2000		JP
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	WO94/09446		Apr., 1994		WO
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Other References

Partial European Search Report for Application No. EP 03 00 2534; The Hague; Mailed Jun. 11, 2004. cited by other . Notice of Reasons of Rejection for Japanese Patent Application No. 2003-020892; Mailed Apr. 27, 2004; and English translation thereof. cited by other . Williams, Gerald O.; "Iris Recognition Technology"; IEEE Arospace and Electronic Systems Magazine; IEEE Inc.; New York, U.S.; vol. 12, No. 4; Apr. 1, 1997; pp. 23-29; XP000677464. cited by other . European Search Report for Application No. EP 03 00 2534; Mailed Aug. 10, 2004. cited by other.

Primary Examiner: Wu; Jingge
Assistant Examiner: Carter; Aaron
Attorney, Agent or Firm: Harness, Dickey & Pierce, P.L.C.

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Claims

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What is claimed is:

1. A personal authentication method comprising the steps of: capturing, by using an image capturing device, a plurality of iris images of a person to be authenticated in which positions of extraneous light reflection are respectively different; and performing authentication by using said plurality of iris images and registered iris data.

2. The personal authentication method of claim 1, wherein said image capturing device instructs said person on a facing direction in said capturing step.

3. The personal authentication method of claim 1, wherein said image capturing device guides a sight line of said person in said capturing step.

4. The personal authentication method of claim 1, wherein a position of a camera in said image capturing device is changed in said capturing step.

5. The personal authentication method of claim 1, wherein said image capturing device includes a plurality of cameras, and said image capturing device captures said plurality of iris images by using said plurality of cameras in said capturing step.

6. The personal authentication method of claim 1, wherein said image capturing device instructs said person on a direction for moving his or her hand holding said image capturing device in said capturing step.

7. The personal authentication method of claim 1, wherein said authentication step includes the steps of: extracting iris data corresponding to features for authentication respectively from said plurality of iris images; obtaining a plurality of comparison results by respectively comparing said extracted iris data with said registered iris data; and obtaining an ultimate comparison score by integrating said plurality of comparison results, and wherein the authentication is performed on the basis of said ultimate comparison score.

8. The personal authentication method of claim 1, wherein said authentication step includes the steps of: extracting iris data corresponding to features for authentication respectively from said plurality of iris images; generating integrated iris data by integrating said extracted iris data; and obtaining a comparison result by comparing said integrated iris data with said registered iris data, and wherein the authentication is performed on the basis of said comparison result.

9. The personal authentication method of claim 1, wherein said authentication step includes the steps of: generating an integrated iris image by integrating said plurality of iris images; extracting iris data corresponding to a feature for authentication from said integrated iris image; and obtaining a comparison result by comparing said iris data with said registered iris data, and wherein the authentication is performed on the basis of said comparison result.

10. A personal authentication method comprising the steps of: extracting iris data corresponding to features for authentication respectively from a plurality of iris images of a person to be authenticated; obtaining a plurality of comparison results by respectively comparing said extracted iris data with registered iris data; and selecting, from said plurality of comparison results, a comparison result with a comparison score not less than a given value or a comparison result with a comparison score not more than a given value, wherein the authentication is performed on the basis of said selected comparison result.

11. A personal authentication method comprising the steps of extracting iris data corresponding to features for authentication respectively from a plurality of iris images of a person to be authenticated; obtaining a plurality of comparison results by respectively comparing said extracted iris data with registered iris data; and obtaining a synthesized comparison result by dividing each of said plurality of comparison results into a plurality of blocks and synthesizing said plurality of comparison results in each of said plurality of blocks, wherein the authentication is performed on the basis of said synthesized comparison result.

12. A personal authentication method comprising the steps of: capturing an iris image of a person to be authenticated; determining, on the basis of said iris image, whether or not extraneous light reflection is caused in said iris image; and capturing a plurality of iris images of said person in which positions of the extraneous light reflection are respectively different and performing authentication by using said plurality of iris images, when it is determined that the extraneous light reflection is caused.

13. The personal authentication method of claim 12, wherein said determining step includes the steps of: obtaining a comparison result by comparing said iris image with registered iris data; dividing said comparing result into a plurality of blocks and calculating a comparison score of each of said plurality of blocks; and determining that the extraneous light reflection is caused when the number of blocks each having the comparison score not less than a first threshold value is not more than a second threshold value.

14. A personal authentication method comprising the steps of: measuring an intensity of near-infrared light in an environment where an iris image is captured; and capturing a plurality of iris images of a person to be authenticated in which positions of extraneous light reflection are respectively different and performing authentication by using said plurality of iris images, when said intensity is not less than a threshold value.

15. A personal authentication apparatus comprising: an image capturing unit for capturing a plurality of iris images of a person to be authenticated in which positions of extraneous light reflection are respectively different; and an authentication processing unit for performing authentication by using said plurality of iris images captured by said image capturing unit and registered iris data.

16. The personal authentication apparatus of claim 15, wherein said image capturing unit includes: a camera; and means for instructing said person on a facing direction.

17. The personal authentication apparatus of claim 15, wherein said image capturing unit includes: a camera; and means for guiding a sight line of said person.

18. The personal authentication apparatus of claim 15, wherein said image capturing unit includes: a camera; and means for changing a position of said camera with respect to said personal authentication apparatus.

19. The personal authentication apparatus of claim 15, wherein said image capturing unit includes a plurality of cameras to be used for capturing said plurality of iris images.

20. The personal authentication apparatus of claim 15, wherein said image capturing unit includes: a camera; and means for instructing a person to be authenticated on a direction for moving his or her hand holding said device.

21. The personal authentication method of claim 1, wherein the extraneous light is sunlight.

22. The personal authentication method of claim 12, wherein the extraneous light is sunlight.

23. The personal authentication method of claim 14, wherein the extraneous light is sunlight.

24. The personal authentication apparatus of claim 15, wherein the extraneous light is sunlight.

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Description

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BACKGROUND OF THE INVENTION

The present invention relates to a technique for personal authentication utilizing iris images, and more particularly, it relates to a technique to improve the accuracy in iris authentication in outdoor light such as sunlight.

Recently, a technique for personal authentication utilizing iris images has started to be employed for management of entrances/exits of an important institution, authentication of a user of an ATM (Automated Teller Machine) of a bank or the like, authentication for logging in a PC and the like. In general, the iris authentication is performed through the following steps:

1. An iris image of a person is captured with a near-infrared illumination (ex. LED);

2. The iris image is analyzed to extract an iris code; and

3. The extracted iris code is compared with a previously registered iris code, and when a difference (distance) between these codes is not more than a threshold value, the person is authenticated.

In this case, the near-infrared light is used for lighting because it is not perceptible for man and hence does not dazzle the person to be authenticated. In addition, most of the people on the earth have dark brown irises (although some people have blue or gray irises, they are globally minor), and the iris pattern of a dark brown iris is difficult to visually recognize in visible light but its image can be captured with high contrast in the near-infrared light. The iris pattern of a blue or gray iris can be also captured in the near-infrared light.

As described above, the iris authentication has been started to be employed for the management of entrances/exits and the authentication of users of ATMs and for logging in PCs, and in most cases, the iris authentication is employed from a premise that it is performed indoor with a small quantity of near-infrared component of outdoor light. In the case where the iris authentication is performed in outdoor light, such as the sunlight, including a large quantity of near-infrared component, near-infrared light from the sun and the like and near-infrared light reflected by objects irradiated by the sun and the like are widely reflected in the eye. Also, in the case where the face is directly exposed to the sunlight, the shadow of the eyelid or eyelashes may be cast over the iris region. These factors can increase a false rejection rate (FRR). However, it is almost impossible that an obtained iris pattern accidentally resembles an iris pattern of another person due to such reflection and shadow of the eyelid or eyelashes. Therefore, there is little possibility of increase of a false acceptance rate (FAR).

Mostly, the facilities for an ATM is located in the vicinity of the entrance of a building facing on a street. Methods for preventing the influence of the outdoor light are described in patent documents 1 and 2. According to the patent document 1, reflection of the extraneous light is prevented as follows: First polarizing means is provided outside a lens of a camera for capturing an iris image, second polarizing means is provided between an iris authentication apparatus and the source of extraneous light (for example, on a window), and the first and second polarizing means have different polarization directions. Alternatively, according to the patent document 2, the reflection of the extraneous light on an eye is prevented by providing, in a position from which the extraneous light enters the eye (for example, on a window), a non-visible light non-penetrating filter for reflecting or absorbing a non-visible light component lighting the eye out of frequency components of the extraneous light.

As alternative means for preventing the reflection, shielding means such as an eye cup is provided in front of a camera, and a person to be authenticated (hereinafter simply referred to as a user) looks into the shielding means for capturing an image of his/her iris.

Furthermore, patent documents 3, 4, 5 and 6 describe methods for dealing with reflection of lighting means itself used for lighting an eye, which is not the outdoor light.

According to the patent document 3, the head of a user is expected to move while a plurality of iris images are being captured, and the plural iris images are used for reducing the influence of the reflection. First, one image and a registered image are subjected to matching, and a consistent portion therebetween is added to a matching image. Thereafter, the other images are also subjected to the matching with the registered image, so as to successively add consistent portions to the matching image. The ultimate matching image thus formed is compared with the registered image for the authentication.

In all the techniques disclosed in the patent documents 4, 5 and 6, a plurality of lighting means installed in different positions are used. Specifically, an eye is lighted with the plural lighting means at different timings, so as to capture a plurality of iris images respectively at the different lighting timings. A plurality of iris images (or features or comparison results) in which the positions of the reflection of the lighting means are respectively different are synthesized, so as to generate an iris image (or a feature or comparison result) that is free from the influence of the reflection.

Patent document 1: Japanese Laid-Open Patent Publication No. 10-21392

Patent document 2: Japanese Laid-Open Patent Publication No. 2000-185032

Patent document 3: Japanese Laid-Open Patent Publication No. 9-212644

Patent document 4: Japanese Laid-Open Patent Publication No. 10-162146

Patent document 5: Japanese Laid-Open Patent Publication No. 11-203478

Patent document 6: Japanese Laid-Open Patent Publication No. 2001-167252

The aforementioned conventional techniques have, however, the following disadvantages:

The techniques disclosed in the patent documents 1 and 2 are described from a premise of the facilities such as an ATM, and hence, both the techniques need a large-scale apparatuses and need a large cost for practice. Therefore, these techniques are disadvantageously limited in the applicable use.

Also, in the method in which the shielding means such as an eye cup is provided in front of a camera and a user looks into the shielding means for capturing the image of an iris, an advantage of the iris authentication, that is, contactless authentication, is spoiled. Therefore, this method is not preferable from the viewpoint of sanitation and user interface.

Furthermore, the patent document 3 originally describes the countermeasure against not the reflection of the extraneous light but the reflection of the lighting means equipped on the authentication apparatus. Moreover, although the head of a user is expected to naturally move, when the head does not move, the influence of the reflection cannot be reduced and hence the effect cannot be attained. Furthermore, even if the head moves, the user stands in front of the apparatus for the authentication and hence dare not turn his/her eyes largely off the apparatus. Accordingly, there is little possibility that the position of the reflection is changed.

Also, the methods described in the patent documents 4, 5 and 6 using plural lighting means are useful as the countermeasure against the reflection of the lighting means equipped on the authentication apparatus but are useless against the reflection in the outdoor light.

SUMMARY OF THE INVENTION

An object of the invention is, in personal authentication utilizing an iris image, preventing an authentication accuracy from lowering even when extraneous light is reflected on an iris.

In personal authentication of this invention, a plurality of iris images of a person to be authenticated in which the positions of extraneous light reflection are respectively different are captured, and authentication is performed by using the plural iris images and registered iris data.

According to this invention, the authentication can be performed with the influence of the extraneous light reflection reduced by using a plurality of iris images in which the positions of the extraneous light reflection are respectively different. Therefore, personal authentication can be executed even in the outdoor light with the false rejection rate suppressed.

Alternatively, the personal authentication method of this invention includes the steps of extracting iris data corresponding to features for authentication respectively from a plurality of iris images of a person to be authenticated; obtaining a plurality of comparison results by respectively comparing the extracted iris data with registered iris data; and selecting, from the plurality of comparison results, a comparison result with a comparison score not less than a given value or a comparison result with a comparison score not more than a given value, and the authentication is performed on the basis of the selected comparison result.

According to this invention, a comparison result having a comparison score larger or smaller than the given value, namely, a comparison result that is highly probably obtained from the person to be authenticated as a registered person, is selected from the plural comparison results. Therefore, not only the false rejection ratio but also the false acceptance ratio can be suppressed.

Alternatively, the personal authentication method of this invention includes the steps of extracting iris data corresponding to features for authentication respectively from a plurality of iris images of a person to be authenticated; obtaining a plurality of comparison results by respectively comparing the extracted iris data with registered iris data; and obtaining a synthesized comparison result by dividing each of the plurality of comparison results into a plurality of blocks and synthesizing the plurality of comparison results in each of the plurality of blocks, and the authentication is performed on the basis of the synthesized comparison result.

According to this invention, the plural comparison results are synthesized in each block, and therefore, the synthesized comparison result is less affected by noise in the comparison results as compared with the case where they are synthesized in each one-dimensional unit of the feature (that is, one bit in a binary feature). Therefore, a stable comparison result can be synthesized.

Alternatively, the personal authentication method of this invention includes the steps of capturing an iris image of a person to be authenticated; determining, on the basis of the iris image, whether or not extraneous light reflection is caused in the iris image; and capturing a plurality of iris images of the person in which positions of the extraneous light reflection are respectively different and performing authentication by using the plurality of iris images, when it is determined that the extraneous light reflection is caused.

According to this invention, in the case where it is determined that the extraneous light reflection is caused in the iris image obtained from a person to be authenticated as a registered person, a plurality of iris images are captured. Therefore, the person to be authenticated can be free from troublesomeness of always capturing a plurality of iris images.

Alternatively, the personal authentication method of this invention includes the steps of measuring an intensity of near-infrared light in an environment where an iris image is captured; and capturing a plurality of iris images of a person to be authenticated in which positions of extraneous light reflection are respectively different and performing authentication by using the plurality of iris images, when the intensity is not less than a threshold value.

According to this invention, in the case where the intensity of the near-infrared light is so high that the reflection is easily caused, a plurality of iris images are captured. Therefore, the person to be authenticated can be free from the troublesomeness of always capturing a plurality of iris images.

Also, the device of this invention for capturing an iris image for personal authentication, includes a camera; and means for instructing a person to be authenticated on a direction for moving his or her hand holding the device.

Thus, the device instructs the person to be authenticated on the direction for moving the hand, and hence, a plurality of iris images can be easily captured.

The first personal authentication method of this invention includes the steps of capturing, by using an image capturing device, a plurality of iris images of a person to be authenticated in which positions of extraneous light reflection are respectively different; and performing authentication by using the plurality of iris images and registered iris data.

In one aspect of the first personal authentication method, the image capturing device instructs the person on a facing direction in the capturing step.

In another aspect of the first personal authentication method, the image capturing device guides a sight line of the person in the capturing step.

In another aspect of the first personal authentication method, a position of a camera in the image capturing device is changed in the capturing step.

In another aspect of the first personal authentication method, the image capturing device includes a plurality of cameras, and the image capturing device captures the plurality of iris images by using the plurality of cameras in the capturing step.

In another aspect of the first personal authentication method, the image capturing device instructs the person on a direction for moving his or her hand holding the image capturing device in the capturing step.

In another aspect of the first personal authentication method, the authentication step includes the steps of extracting iris data corresponding to features for authentication respectively from the plurality of iris images; obtaining a plurality of comparison results by respectively comparing the extracted iris data with the registered iris data; and obtaining an ultimate comparison score by integrating the plurality of comparison results, and the authentication is performed on the basis of the ultimate comparison score.

In another aspect of the first personal authentication method, the authentication step includes the steps of extracting iris data corresponding to features for authentication respectively from the plurality of iris images; generating integrated iris data by integrating the extracted iris data; and obtaining a comparison result by comparing the integrated iris data with the registered iris data, and the authentication is performed on the basis of the comparison result.

In another aspect of the first personal authentication method, the authentication step includes the steps of generating an integrated iris image by integrating the plurality of iris images; extracting iris data corresponding to a feature for authentication from the integrated iris image; and obtaining a comparison result by comparing the iris data with the registered iris data, and the authentication is performed on the basis of the comparison result.

The second personal authentication method of this invention includes the steps of extracting iris data corresponding to features for authentication respectively from a plurality of iris images of a person to be authenticated; obtaining a plurality of comparison results by respectively comparing the extracted iris data with registered iris data; and selecting, from the plurality of comparison results, a comparison result with a comparison score not less than a given value or a comparison result with a comparison score not more than a given value, and the authentication is performed on the basis of the selected comparison result.

The third personal authentication method of this invention includes the steps of extracting iris data corresponding to features for authentication respectively from a plurality of iris images of a person to be authenticated; obtaining a plurality of comparison results by respectively comparing the extracted iris data with registered iris data; and obtaining a synthesized comparison result by dividing each of the plurality of comparison results into a plurality of blocks and synthesizing the plurality of comparison results in each of the plurality of blocks, and the authentication is performed on the basis of the synthesized comparison result.

The fourth personal authentication method of this invention includes the steps of capturing an iris image of a person to be authenticated; determining, on the basis of the iris image, whether or not extraneous light reflection is caused in the iris image; and capturing a plurality of iris images of the person in which positions of the extraneous light reflection are respectively different and performing authentication by using the plurality of iris images, when it is determined that the extraneous light reflection is caused.

In one aspect of the fourth personal authentication method, the determining step includes the steps of obtaining a comparison result by comparing the iris image with registered iris data; dividing the comparing result into a plurality of blocks and calculating a comparison score of each of the plurality of blocks; and determining that the extraneous light reflection is caused when the number of blocks each having the comparison score not less than a first threshold value is not more than a second threshold value.

The fifth personal authentication method of this invention includes the steps of measuring an intensity of near-infrared light in an environment where an iris image is captured; and capturing a plurality of iris images of a person to be authenticated in which positions of extraneous light reflection are respectively different and performing authentication by using the plurality of iris images, when the intensity is not less than a threshold value.

The personal authentication apparatus of this invention includes an image capturing unit for capturing a plurality of iris images of a person to be authenticated in which positions of extraneous light reflection are respectively different; and an authentication processing unit for performing authentication by using the plurality of iris images captured by the image capturing unit and registered iris data.

In one aspect of the personal authentication apparatus, the image capturing unit includes a camera; and a section for instructing the person on a facing direction.

In another aspect of the personal authentication apparatus, the image capturing unit includes a camera; and a section for guiding a sight line of the person.

In another aspect of the personal authentication apparatus, the image capturing unit includes a camera; and a section for changing a position of the camera with respect to the personal authentication apparatus.

In another aspect of the personal authentication apparatus, the image capturing unit includes a plurality of cameras to be used for capturing the plurality of iris images.

The device of this invention for capturing an iris image for personal authentication, includes a camera; and a section for instructing a person to be authenticated on a direction for moving his or her hand holding the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a personal authentication method utilizing an iris image according to Embodiment 1 of the invention;

FIG. 2 is a diagram of a cellular phone with an authentication function described as an example of an image capturing device of this invention;

FIG. 3 is a schematic diagram of the internal arrangement of the cellular phone of FIG. 2;

FIG. 4 is a diagram of an iris image in which extraneous light is reflected in an iris region;

FIG. 5 is a diagram of iris images captured with the direction of the eye ball (the direction of the sight line) respectively changed;

FIG. 6 is a diagram of iris images captured with the facing direction respectively changed;

FIG. 7 is a diagram for showing the outer edge of a pupil and the outer edge of an iris;

FIG. 8 is a diagram of an iris image expressed by using an xy rectangular coordinate system;

FIG. 9 is a diagram of an iris image expressed by using an r.theta. polar coordinate system;

FIG. 10 is a diagram for showing analysis zones obtained by dividing an iris into eight ring-shaped portions;

FIGS. 11A, 11B and 11C are diagrams for showing a method for generating an iris code;

FIG. 12 is a diagram for showing a method for comparing two iris codes with rotation compensation;

FIG. 13 is a diagram for showing a result of comparison of N iris codes with a registered iris code;

FIG. 14 is a flowchart of processing A4 of FIG. 1 performed in synthesis in each bit;

FIG. 15 is a flowchart of the processing A4 of FIG. 1 performed in synthesis in each block;

FIGS. 16A and 16B are diagrams for showing a method for dividing an iris region of an iris image into blocks;

FIG. 17 is an outline diagram of a cellular phone with an authentication function equipped with a plurality of cameras;

FIG. 18 is an outline diagram of a door phone with an authentication function equipped with guiding lamps;

FIG. 19 is a flowchart of a personal authentication method utilizing iris authentication according to Embodiment 2 of the invention;

FIG. 20 is a flowchart for showing detailed procedures in processing B3 of FIG. 19;

FIG. 21 is a flowchart of a personal authentication method utilizing iris authentication according to a modification of Embodiment 2 of the invention;

FIG. 22 is a flowchart for showing detailed procedures in processing B31 of FIG. 21;

FIG. 23 is a flowchart of a personal authentication method utilizing iris authentication according to Embodiment 3 of the invention;

FIG. 24 is a flowchart for showing detailed procedures in processing C2 of FIG. 23;

FIG. 25 is a flowchart of a personal authentication method including processing for determining, at an image level, whether or not extraneous light is reflected; and

FIG. 26 is a flowchart of a personal authentication method including processing for determining whether or not the authentication is performed in the outdoor light.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the invention will now be described with reference to the accompanying drawings.

Herein, "extraneous light" means light other than that of lighting used for capturing iris images and included in an iris authentication apparatus or an image capturing device. Also, "reflection" means a luminance pattern formed due to spatially uneven "extraneous light" in an iris region of a captured iris image.

Embodiment 1

FIG. 1 is a flowchart of a personal authentication method utilizing iris authentication according to Embodiment 1 of the invention. FIG. 2 is a diagram for showing the appearance of a cellular phone with an authentication function described as an example of an image capturing device to be used in practicing the personal authentication method of this embodiment, and FIG. 3 is a diagram for showing the internal arrangement of the cellular phone with the authentication function of FIG. 2. It is assumed in this embodiment that a user (a person to be authenticated) performs the iris authentication in outdoor light by using the cellular phone with the authentication function as shown in FIG. 2.

In the cellular phone 10 with the authentication function of FIG. 2, a camera 11 for capturing an iris image and lighting 12 are additionally provided to a general cellular phone. This cellular phone 10 includes, in addition to the camera 11 and the lighting 12, a monitor 13, operation buttons 14, a speaker 15, a microphone 16, an antenna 17 and the like. One or a plurality of near-infrared LEDs are used as the lighting 12. The lighting of the near-infrared light is used so as not to dazzle a user and so as to capture a dark brown iris pattern with high contrast. The camera 11 is provided with a visible light cut filter so as to receive a near-infrared component alone. On the monitor 13, an iris image to be captured and an authentication result are displayed. In the case where an iris image is captured in light including a large quantity of near-infrared component, such as light from the sunlight and an incandescent lamp, there is no need to always provide the lighting, and when it is provided, there is no need to always light it.

Also, in the internal arrangement shown in FIG. 3, a camera control unit 22, a lighting control unit 23 and a monitor control unit 24 are connected to a main control unit 27 in authentication means 21. The camera control unit 22 controls the camera 11 to capture an iris image, and captured iris images are stored in an image memory 25. An authentication processing unit 26 performs authentication processing by using the iris images stored in the image memory 25. The lighting control unit 23 controls the lighting 12 so as to light an iris region in synchronization with timing of capturing each image. The monitor control unit 24 controls a display screen of the monitor 13.

Now, processing performed in the personal authentication method of this embodiment will be described in accordance with the flow shown in FIG. 1.

First, a user holds the cellular phone 10 with the authentication function shown in FIG. 2, and captures, in the outdoor light, a plurality of (N) iris images in which positions of extraneous light reflection are respectively different (A1). In capturing the images, the user holds the cellular phone 10 in a position away from his/her eye by a predetermined distance (of, for example, approximately 20 cm when the camera 11 has a single focus), and while confirming an iris image captured by the camera 11 and displayed on the monitor 13, adjusts the position of the eye so that the entire iris region can be included in the viewing field and be in focus. Thereafter, he/she presses a camera button for capturing allocated to one of the operation buttons 14. This operation is repeated N times so that the positions of the extraneous light reflection are different in the respective images. Alternatively, after pressing a camera start button once, N frame images can be continuously captured by obtaining an image sequence.

At this point, the phenomenon of extraneous light reflection will be described in detail.

As shown in FIG. 4, in an iris image captured in the outdoor light, the extraneous light is reflected over a wide region. This is because a near-infrared component included in the sunlight (which is an electromagnetic wave with a wide frequency band including UV, visible light, near-infrared light, far infrared light and the like) has large strength, and hence, not only the near-infrared component of the direct sunlight but also near-infrared components reflected from a large number of objects irradiated with the sunlight enter the eye from various angles. (Since an eye ball has a shape close to a sphere, the reflection can be easily caused.)

The position of the extraneous light reflection is determined depending upon the positional relationship between the light source (including the reflecting object), the camera and the eye ball, and therefore, one of them is moved to change the position of the reflection. Among them, the light source is difficult to move, and hence, one or both of the camera and the eye ball are moved.

FIG. 5 shows four exemplified iris images captured with the positions of the camera and the face fixed and the direction of the eye ball (the direction of the sight line) alone changed. Also, FIG. 6 shows four exemplified iris images captured with the relative positional relationship between the camera and the eye ball fixed and the facing direction changed among the north, south, east and west. As is understood from FIG. 5, when the eye ball is moved (namely, the direction of the sight line is changed), the position of the reflection with respect to the iris region is changed. Also, as is understood from FIG. 6, the shape of the reflection is changed as the facing direction is changed.

In this embodiment, in order to capture a plurality of iris images in which the positions of the extraneous light reflection are respectively different, the device as shown in FIG. 2 is used for instructing the user on the facing direction or guiding the direction of the sight line of the user. For example, the facing direction is displayed on the monitor 13 with an arrow (in which case the monitor 13 and its control unit correspond to means for instructing the facing direction), the facing direction is instructed with a voice from the speaker 15 (in which case the speaker 15 and its control unit correspond to the means for instructing the facing direction), or a specific image such as the image of a character is displayed on the monitor 15 so as to move the image to a direction for guiding the sight line (in which case the monitor 13 and its control unit correspond to means for guiding the sight line). In this manner, the user can easily grasp without being confused in which direction he/she should turn his/her face or gaze in capturing images, and thus, the device can provide a user-friendly interface. Thus, the plural iris images in which the positions of the extraneous light reflection are respectively different can be easily captured.

The following processing A2 through A5 are executed by the authentication processing unit 26. Herein, a method disclosed in National Publication of translated version No. 8-504979 (International Publication No. WO94/09446, hereinafter referred to as the reference document 1) is employed. The iris authentication method of the reference document 1 is performed roughly through the following steps:

(1) The outer edge of an iris (the boundary between an iris and a sclera) and the outer edge of a pupil (the boundary between a pupil and the iris) are determined so as to cut an iris region out.

(2) The cut iris region is converted from an xy rectangular coordinate system to an r.theta. polar coordinate system.

(3) Analysis zones are determined (by dividing the iris region into 8 ring-shaped zones in the radial direction).

(4) A 2-d Gabor filter of multi-scale is applied, and a signal output from the Gabor filter is binarized to obtain an iris code.

(5) A registered iris code previously registered is compared with the iris code obtained in the authentication (through exclusive OR), so as to calculate a hamming distance between the two codes.

(6) When the hamming distance is not more than a threshold value, the user is authenticated to accept, and otherwise, the user is rejected as another person.

FIG. 7 is a diagram for showing the positions of the outer edge of an iris and the outer edge of a pupil, and FIG. 8 is a diagram, expressed by using the xy rectangular coordinate system, of a region surrounded between the outer edge of the iris and the outer edge of the pupil cut out as the iris region. At this point, the influence of parallel movement of the iris region is absorbed. Also, FIG. 9 is a diagram of the iris region expressed by using the r.theta. polar coordinate system with the center of the pupil set as the center of the coordinate (obtained through the conversion in step (2)). The actual outer edges of an iris and a pupil are not accurately circular, but if they are approximated to a circle, the center of the pupil and the center of the iris are not concentric (but eccentric). However, when a value in the redirection is set to 0 on the outer edge of the pupil and to 1 on the outer edge of the iris, the eccentricity, a difference in the dilation of the pupil and the influence of expansion/reduction can be absorbed.

FIG. 10 is a diagram of the 8 ring-shaped analysis zones determined in step (3). FIGS. 11A through 11C are diagrams for showing generation of the iris code in step (4). A luminance signal as shown in FIG. 11A is obtained after determining the analysis zones, the Gabor filter is applied to give a signal as shown in FIG. 11B and this signal is binarized as shown in FIG. 11C. Although the signal is actually two-dimensional, it is herein shown as a one-dimensional signal for simplification.

FIG. 11A shows an angular direction luminance signal obtained in one of the 8 ring-shaped zones. The Gabor filter of multi-scale is actually applied, and there are a real part and an imaginary part even in a Gabor filter of single-scale. FIGS. 11B and 11C show the signals obtained by applying a real part of the Gabor filter of a given scale. The position of each bit in the iris code shown in FIG. 11C resulting from the binarization can be made to correspond to a given position in the iris image.

First, the captured N iris images are subjected to feature extraction, so as to respectively generate N iris codes as iris data corresponding to features for the authentication (A2). In the processing A2, the aforementioned steps (1) through (4) are performed on each of the N iris images in which the positions of the extraneous light reflection are respectively different, so as to generate the N iris codes. At this point, when steps (1) through (3) are performed on each image, an iris code in which the influences of the parallel movement, the expansion/reduction, the difference in the dilation of the pupil and the eccentricity of the pupil are absorbed is generated with respect to each iris region of the plural iris images.

Next, the N iris codes are respectively compared with the registered iris code previously registered as registered iris data of the user, so as to obtain N comparison results (A3). In each embodiment of this invention, corresponding bits are compared between the two iris codes, so as to generate, as the "comparison result", a bit string showing match/mismatch between the compared bits. Since an XOR operation is used for comparing the bits, when they match, "0" is given as a bit value, and when they do not match, "1" is given as a bit value. Also, such a bit value expressing the match/mismatch is used as a "determination result".

In the processing A3, the above-described step (5) is performed. At this point, there may be a shift in the angular direction derived from the inclination of the face or the rotation of the eye ball between the registered iris code and the iris code for authentication. In order to compensate this shift, the iris code for authentication is rotated in a previously determined range for matching, so that the minimum hamming distance can be obtained as the ultimate hamming distance. This processing is shown in FIG. 12. In FIG. 12, for the sake of simplification, a real part of the Gabor filter of a given scale is applied for the analysis, and one of the 8 ring-shaped zones is shown.

FIG. 13 is a diagram for showing the result of the comparison between the registered iris code and the N iris codes for authentication. The iris codes 1 through N for authentication shown in FIG. 13 have already been subjected to the rotation compensation matching so as to be shifted to positions for minimizing the hamming distances. Specifically, the ith bit positions in the codes all correspond to the same position in the iris pattern. Also, in FIG. 13, each iris code for authentication is divided into M blocks, and a block having a hamming distance larger than a predetermined threshold value TH2 (of 0.30 in this embodiment) is shown as a black block.

According to the comparison result shown in FIG. 13, the iris codes 1, 2 and N for authentication respectively have hamming distances of 0.31, 0.33 and 0.34. A hamming distance is 0.5 when two codes are not correlated with each other at all. Hamming distances obtained between two different persons are distributed around 0.5, but a hamming distance is shifted to be slightly smaller when the rotation compensation matching is performed. In the case where a threshold value TH1 of the hamming distance for the authentication is 0.30, these iris codes for authentication are all rejected when singly used.

However, as shown in FIG. 13, although the hamming distances of the most blocks are not more than the threshold value TH2, the hamming distance HD of the entire iris code for authentication is larger than the threshold value TH1 because merely some blocks (the black blocks) have large hamming distances. It seems that these blocks have the large hamming distances HD because of the extraneous light reflection.

Therefore, in this embodiment, a plurality of comparison results are synthesized and integrated to generate an ultimate comparison score (A4). Thus, in the case where the positions of the extraneous light reflection are respectively different in the plural iris images, the influence of the extraneous light reflection on the accuracy in the personal authentication can be eliminated. Herein, a "comparison score" means a scholar value representing the matching degree resulting from the comparison between two iris codes. In each embodiment of the invention, a ratio in the number of mismatch bits to all compared bits, namely, the hamming distance, is used as the "comparison score".

For the integration of the comparison results, the comparison results may be synthesized in each bit or in each block.

<Synthesis in Each Bit>

FIG. 14 is a flowchart of detailed procedures in the processing A4 performed when the comparison results are synthesized in each bit. In FIG. 14, comparison results each having a hamming distance not more than a predetermined threshold value TH3 (>TH1) are first selected from the N comparison results (A401). Next, attention is paid to the ith bit position (A402), and if any bit in the attended bit position of the selected comparison results matches with the corresponding one of the registered iris code, the ultimate determination result of that bit position is determined to match (A403). These procedures of steps A402 and A403 are executed on all the bit positions (A404). The number of ultimately mismatch bits is normalized with the total number of bits, so as to calculate a hamming distance as the ultimate comparison score (S405).

At this point, in the case where a person who is not the registered person captures his/her N (which is a large number) iris images, the probability that any one of the N iris codes matches with the registered iris code in a given bit position is closer to "1" (because the probability of match/mismatch is 0.5 when there is no comparison between two codes). This also applies to the case where a plurality of persons who are not the registered person capture N iris images by turn. Therefore, if all the comparison results obtained from the plural iris images are used for the authentication, the probability that a person who is not the registered person is authenticated by mistake is increased.

Accordingly, in step A401, a comparison result having a hamming distance larger than the threshold value TB3 is excluded for the following steps because it is highly probably obtained from an iris image of a person who is not the registered person. Specifically, merely comparison results each having a hamming distance larger than the threshold value TH1 for the authentication and smaller than the predetermined threshold value TH3 are accepted for the following steps under interpretation that "the hamming distance exceeds the threshold value TH1 because there is extraneous light reflection in the iris image of the registered person". In this manner, the increase of the false acceptance ratio (FAR), that is, a ratio of authenticating a person not to be authenticated by mistake, can be suppressed. In the case where an index that has a large value when there is high comparison and has a small value when there is low comparison is used instead of the hamming distance, comparison results each having a score not less than a predetermined value are selected in step A401.

Also, in step S403, for example, with respect to the attended bit position, the N comparison results may be subjected to a majority decision in the match/mismatch, so that the major result can be regarded as the ultimate determination result of that bit position. Alternatively, the ultimate determination result of the attended bit position may be determined depending upon whether or not the ratio of matches in the N comparison results is larger than a predetermined threshold value. Further alternatively, with respect to the attended bit position, the ratio of matches in the N comparison results is obtained as a score of that bit position, so that an average of the scores of all the bit positions can be obtained as the ultimate comparison score.

Furthermore, with respect to the attended bit position, a weighted average of the N comparison results may be used for obtaining the ultimate determination result of that bit position. An example of the specific method is as follows:

First, a weight w.sub.k (0.ltoreq.w.sub.k.ltoreq.1; wherein k is a comparison result number) that increases as the reliability of a comparison result is higher is prepared. For example, the weight is defined by the following equation (5):

.times. ##EQU00001## wherein x.sub.k is a hamming distance of the kth comparison result. In other words, a comparison result with a smaller hamming distance is judged to have high reliability and hence is provided with a larger weight. In this equation, the denominator is a normalized term for making the sum of the weights w.sub.k to be 1.

Then, a value r.sub.i of the ith bit of a synthesized comparison result is determined by using the following equation (6):

.times..times..times..times..times..times..times.<.times..times..times.- .times..times. ##EQU00002## wherein r.sub.k,j is a value of the ith bit of the kth comparison result. In this example, the common weight w.sub.k is used for all the bit positions of the kth comparison result.

Alternatively, different weights may be used for the respective bit positions as follows:

First, a weight w.sub.k,i (0.ltoreq.w.sub.k,i.ltoreq.1; k is a comparison result number; and i is a bit position) that increases as the reliability of a comparison result is higher is prepared. For example, the weight is defined by using the following equation (7):

.times. ##EQU00003## wherein x.sub.k,i is a local hamming distance in the vicinity of the ith bit of the kth comparison result. The word "local" means being local on the iris image. In other words, a bit value r.sub.k,i with a small local hamming distance is judged to have high reliability and hence is provided with a large weight. In this equation, the denominator is a normalized term for making the sum of the weights w.sub.k,i with respect to k to be 1.

Then, a value r.sub.i of the ith bit of a synthesized comparison result is determined by using the following equation (8):

.times..times..times..times..times..times..times.<.times..times..times.- .times..times. ##EQU00004##

Also, in the equation (7), x.sub.k,i may be a luminance value (of a point or a local area) on the iris image corresponding to the ith bit of the kth comparison result. In other words, a bit corresponding to a portion with a large luminance value is judged to highly probably have an unstable value due to the reflection and have low reliability, and hence is provided with a smaller weight.

Needless to say, another weight apart from those described above may be used as far as it has a larger value as the reliability of the corresponding bit is higher.

<Synthesis in Each Block>

FIG. 15 is a flowchart for showing detailed procedures in the processing A4 performed in synthesizing the comparison results in each block. In FIG. 15, comparison results each having a hamming distance not more than the predetermined threshold value TH3 (>TH1) are first selected from the N comparison results (A411). Next, the iris code for authentication obtained from each of the selected comparison results is divided into M blocks (A412). The block division is performed as follows: The iris image is previously divided, and when pixels corresponding to bits of the iris code belong to the same block in the iris image, these bits of the iris code are made to belong to the same block. The iris image is divided, for example, concentrically and radially