Patent Application
20060262965
The present invention relates to an iris authentication apparatus used for personal authentication or the like and, more specifically, to a pupil detection device for detecting the position of a pupil from an eye image (image including an eye).
In recent years, various methods for detecting the position of a pupil from an eye image are proposed. For example, a method of binarizing image data of the eye image (hereinafter, abbreviated as “eye image data”) and detecting a circular area in an area of low-luminance level is known. A method of calculating a contour integral of an image luminance I (x, y) with respect to an arc of a circle having a radius r and center coordinates (xo, yo), and calculating a partial derivative of this r-related amount in accordance with increase in the radius r is known. The aforementioned structure in the related art is disclosed, for example, in JP-T-8-504979.
In order to detect the pupil with high degree of accuracy using these methods, it is necessary to process a huge amount of image data at high-speed, and hence it is difficult to process the image data of the eye image on real time basis even though a large CPU having a high processing capability or a bulk memory in the status quo. Also, when the processing amount of the CPU is reduced to a degree which enables real time processing of the image data, there may arise a problem such that the detection accuracy is lowered.
The present invention provides a pupil detection device and an iris authentication apparatus which can detect the position of a pupil at high-speed and with high degree of accuracy.
The pupil detection device of the present invention includes an image data extraction unit, a contour integrating unit, a pupil radius detection unit, and a pupil position detection unit. The image data extraction unit determines a plurality of circles on an eye image as integrating circles respectively, and extracts the eye image data along the integrating circles. A contour integrating unit integrates the image data extracted by the image data extraction unit along the respective circumferences of the integrating circles. A pupil radius detection unit detects that an integrated value obtained by the contour integrating unit has changed stepwise with respect to the radius of the integrating circle. A pupil position detection unit detects that the center coordinates of the integrating circle as pupil position coordinates when the pupil radius detection unit detects the change stepwise. Then, the plurality of circles are set concentrically, and the image data extraction unit extracts the plurality of image data simultaneously.
100 iris authentication apparatus
120 image pickup unit
130 illumination unit
140 authentication processing unit
200 pupil detection device
220 image data extraction unit
230 contour integrating unit
250 pupil radius detection unit
260 pointer unit
280 pupil position detection unit
A pupil detection device of the present invention includes an image data extraction unit, a contour integrating unit, a pupil radius detection unit, and a pupil position detection unit. The image data extraction unit determines a plurality of circles on an eye image as integrating circles respectively, and extracts image data of the eye image positioned on the circumferences of the integrating circles. The contour integrating unit integrates the image data extracted by the image data extraction unit along the respective circumferences of the integrating circles.
The pupil radius detection unit detects that an integrated value obtained by the contour integrating unit has changed stepwise with respect to the radius of the integrating circle. The pupil position detection unit detects the center coordinates of the integrating circle as the pupil position coordinates when the pupil radius detection unit detects the change stepwise. The plurality of circles are set concentrically, and the image data extraction unit extracts a plurality of image data simultaneously. In this arrangement, the pupil position can be detected at high-speed and with high degree of accuracy.
The pupil radius detection unit of the pupil detection device of the present invention is preferably configured in such a manner that when a difference value between the integrated value of the two integrating circles having the closest radius out of the plurality of concentric integrating circles is larger than a predetermined threshold, it is considered that the integrated value has changed stepwise with respect to the radius of the integrating circle. Accordingly, the pupil radius detection unit can be configured with a relatively small-scale circuit.
A predetermined threshold in the pupil detection device of the present invention is preferably set to a range between 1/4 to 1/1 times the difference between the integrated value when the integrating circle is located on an iris and the integrated value when the integrating circle is located on a pupil. Accordingly, the probability value of the accurate detection of the pupil can be increased.
A partial frame memory in the image data extraction unit of the pupil detection device of the present invention is preferably configured in such a manner that a plurality of line memories of first-in first-out (FIFO) type are connected. A configuration in which drawing lines for outputting image data corresponding to pixels on the respective circumferences of the plurality of concentric integrating circles are provided is also preferable. Accordingly, the image data extraction unit can be configured using a relatively small-scale circuit.
The pupil detection device of the present invention preferably includes a pointer unit for pointing the center coordinates of the integrating circles, and the pointer unit includes a counter for counting a clock synchronized with a period for acquiring the image data on the partial frame memory. Accordingly, the pointer unit can be configured with a relatively small-scale circuit.
The contour integrating unit of the pupil detection device of the present invention preferably includes a plurality of adders for adding the image data extracted by the image data extraction unit along the respective circumferences of the integrating circles. Accordingly the contour integrating unit can be configured using a relatively small-scale circuit.
The pupil radius detection unit of the pupil detection device of the present invention preferably includes a subtracter, a comparator, and a register. The subtracter calculates a difference value between the integrated values of two integrating circles having the closest radius out of the plurality of concentric integrating circles. The comparator compares the difference value outputted from the subtracter and the predetermined threshold. The register holds the radius of the integrating circle in the case in which the difference value is larger than the predetermined threshold as a radius of pupil. Accordingly, the pupil radius detection unit can be configured with a relatively small-scale circuit.
The pupil position detection unit of the pupil detection device of the present invention is preferably includes the register configured in such a manner that when the pupil radius detection unit detects the radius of the integrating circle as the radius of the pupil, the counter output from the pointer unit which points the center coordinates of the integrating circle in question is held as the pupil position coordinates. Accordingly, the pupil position detection unit can be configured with a relatively small-scale circuit.
An iris authentication apparatus of the present invention is characterized by the provision of the pupil detection device of the present invention. In this arrangement, the iris authentication apparatus in which the pupil detection device which can detect the position of the pupil at high speed and with high degree of accuracy can be provided.
Referring to the drawings, the iris authentication apparatus in which the pupil detection device in the present embodiment will be described below.
Iris authentication apparatus 100 includes image pickup unit 120, pupil detection device 200, authentication processing unit 140, and illumination unit 130. Image pickup unit 120 picks up an eye image of a user. Pupil detection device 200 detects the position of the pupil and the radius thereof from the eye image. Authentication processing unit 140 performs personal authentication by comparing an iris code obtained from the eye image with a registered iris code. Illumination unit 130 irradiates near-infrared ray of a light amount suitable for obtaining the eye image for illuminating the user's eye and the periphery thereof.
Image pickup unit 120 includes guide mirror 121, visible light eliminating filter 122, lens 123, image pickup element 124 and preprocessing unit 125. In the embodiment of the present invention, by using a fixed focal length lens as lens 123, compact and light weighted optical system and cost reduction are realized. Guide mirror 121 guides the user to place the eye to a correct image pickup position by reflecting an image of his/her own eye thereon.
Then, an image of the user's eye is acquired by image pickup element 124 through visible light eliminating filter 122 and lens 123. Preprocessing unit 125 acquires an image data component from the output signal from image pickup element 124, performs processing such as gain adjustment, which is required as the image data, and outputs as the eye image data of the user.
Pupil detection device 200 includes image data extraction unit 220, contour integrating unit 230, pupil radius detection unit 250, pointer unit 260, and pupil position detection unit 280. Although detailed description will be given later, in this arrangement, the pupil is detected from the eye image data outputted from preprocessing unit 125 and the center coordinates of the pupil and the radius thereof is outputted to authentication processing unit 140.
Authentication processing unit 140 cuts out an iris image from the eye image data based on the center coordinates of the pupil outputted from pupil detection device 200. Then, authentication processing unit converts the iris image into a specific iris code which indicates a pattern of the iris, and compares the same with the registered iris code to perform authentication action.
When the obtained eye image is adequate, pupil detection device 200 detects the position of the pupil and the radius thereof. Subsequently, the center coordinates of the pupil and the radius are outputted to authentication processing unit 140 (S20). When the pupil is detected, authentication processing unit 140 cuts out an iris image from the eye image data based on the center coordinates of the pupil (S41). Then, authentication processing unit 140 converts the iris image to a specific iris code which indicates the pattern of the iris (S42), and compares the same with the registered iris code to perform authentication action (S43).
Subsequently, the structure of pupil detection device 200 and the action will be described in detail.
The image including the pupil includes a low luminance area of a disk shape showing the pupil, and a middle luminance area of an annular shape indicating the iris outside thereof exiting therein as shown in
Pupil detection device. 200 detects the positional coordinates (Xo, Yo) and pupil radius Ro based on the idea described above. As shown in
In the embodiment of the present invention, number n of the concentric integrating circles was assumed to be 20, and m=8 pixels were selected from the pixels located on each integrating circle Ci to add the image data to obtain integrated value I of the contour integral. When the center of integrating circles C1-Cn is coincides with the center of the pupil, as described above, integrated value Ii with respect to each integrating circle Ci changes stepwise. Therefore, when difference value ΔIi with respect to radius R of integrated value Ii is obtained, the values reach extremely large value ΔI at a point equal to pupil radius Ro.
On the other hand, since integrated value Ii changes gently when the center of integrating circles C1-Cn do not coincide with the center of the pupil, difference value ΔIi is not a large value. Therefore, by obtaining integrating circle Ci which has large difference value ΔIi larger than difference threshold ΔIth, the position of the pupil and the radius thereof can be obtained.
Then, by moving integrating circles C1-Cn to the respective positions on the eye image, the above-described operation is repeated. In this manner, by obtaining the center coordinates (X, Y) of integrating circle Ci when difference value ΔIi is large and radius R at that time, the positional coordinates (Xo, Yo) of the pupil and pupil radius Ro can be obtained.
In the case of the luminance having 256 levels, an average luminance or the pupil is on the order of level equals 40 and an average luminance of the iris is on the order of level equals 100. Therefore, integrated value I when the integrating circle is located on the pupil is about 40×8=320, and integrated value I when the integrating circle is located on the iris is about 100×8=800. Therefore, difference threshold ΔIth may be set within the range from 480, which is 1/1 time of the difference, to 120, which is 1/4 times of the same.
However, when difference threshold ΔIth is too small, the probability of erroneous detection of things other than the pupil increases, and when it is too large, the possibility that the pupil cannot be detected increases. Therefore, it is preferable to detect an optimal value experimentally to set difference threshold ΔIth. In the embodiment of the present invention, difference threshold ΔIth is set to 2/3 of the difference between the integrated value of the average brightness of the pupil and the integrated value of the average brightness of the iris.
Pupil radius detection unit 250 detects difference value ΔIi of integrated value Ii with respect to radius Ri to compare the same with difference threshold ΔIth. Then by obtaining the radius of the integrated circle in a case in which the difference value is larger than difference threshold ΔIth, the radius of the integrating circle whose integrated value of the concentric integrating circles changes stepwise is detected. Pointer unit 260 shows the center coordinates (X, Y) of integrating circles C1-Cn. Pupil position detection unit 280 holds the center coordinates of the integrating circles in the case in which difference value ΔIi is larger than difference threshold ΔIth.
The image data of m pixels on integrating circle Ci are outputted by the drawing line Li. For clarifying the illustration,
Then, every time when image data sig is entered into partial frame memory 210 by one pixel, the entire image held in partial frame memory 210 is shifted by one pixel. Therefore, the image data outputted from drawing lines Li is also shifted by one pixel. In other words, when image data sig is entered into partial frame memory 210 by one pixel, integrating circles C1-Cn move toward the right by the amount corresponding to one pixel on the eye image. When image data sig which corresponds to one line is entered, integrating circles C1-Cn move downward by the amount corresponding to one line.
In this manner, during the time when the image data which corresponds to one frame is entered into partial frame memory 210, integrating circles C1-Cn scan the entire eye image on the eye image. Therefore, pointer unit 260 counts a clock synchronous with the period of image data acquisition to partial frame memory 210, whereby the center coordinates (X, Y) of the integrating circles is shown by output of X counter 262 and Y counter 264.
As shown in
Pupil radius detection unit 250 includes n−1 subtracters 2521-252n-1, selector 253, comparator 254, and register 255. Subtracters 2521-252n-1 obtain difference of integrated value Ii of each integrating circle Ci with respect to radius R. In other words, difference value ΔIi between integrated values Ii and Ii-1 for circles Ci and Ci-1 which are one-step different in radius out of integrating circles C1-Cn is obtained.
Then, they are compared with difference threshold ΔIth by the comparator 254 via selector 253 in sequence. When difference value ΔIi is larger than difference threshold ΔIth, register 255 holds the radius of the integrating circle in this case. It is also possible to provide register 259 that holds difference value ΔIi at the time when difference value ΔIi is larger than difference threshold ΔIth, and register 259 is shown by a broken line in
Pupil position detection unit 280 is provided with resisters 286, 287, and the values of X counter 262 and Y counter 264 when the pupil is detected by pupil radius detection unit 250 are held in resisters 286, 287.
Subsequently, the operation of pupil detection device 200 will be described using a flowchart. In the following description, the eye image data is sequential scanning data, and one frame includes digital data of 480 lines×640 pixels, for example.
Pupil detection device 200 acquires image data sig which corresponds to one pixel (S51). When the acquired image data is a first data of one frame (S52), Y counter 264 is reset and register 255 of pupil radius detection unit 250 and registers 286, 287 of pupil position detection unit 280 are reset (S53). When acquired data is a first data of one line (S54), X counter 262 is reset and Y counter 264 is incremented (S55). Then, X counter 262 is incremented (S56).
Subsequently, acquired image data is acquired in partial frame memory 210. Then, m image data each time, and n×m image data in total are outputted from each integrating circle Ci out of pixels corresponding n integrating circles C1-Cn on the eye image. Then, adder 230i corresponding to each integrating circle Ci calculates integrated value Ii of each image data, and pupil radius detection unit 250 calculates difference value ΔIi of each integrated value Ii (S57).
Then, difference value ΔIi and difference threshold ΔIth are compared (S58). When difference value ΔIi is larger than difference threshold ΔIth, it is considered that the pupil is detected, and the radius of the integrating circle at this time is held as pupil radius Ro. Simultaneously, pupil position detection unit 280 holds the center coordinates of the integrating circle as pupil position coordinates (Xo, Yo) (S59). When difference value ΔIi is equal to or smaller than difference threshold ΔIth, the procedure goes back to Step S51 to acquire image data of an amount corresponding to the next one pixel.
A series of operations from Step S51 to Step S59 is executed every time when the image data is entered to partial frame memory 210 by an amount corresponding to one pixel. For example, when the frame frequency is 30 Hz and the eye image is composed of 640×480 pixels, the aforementioned series of operations is executed in a period equal to or shorter than 1/(30×640×480) second. When one pixel is entered into partial frame memory 210, the integrating circle moves on the image by an amount corresponding to one pixel, and hence the integrating circle scan the image once while entering the image of one frame. In this manner, the pupil can be detected on real time basis with respect to the image data picked up by image pickup unit 120 with a relatively small-scale circuit.
In the above-described embodiment, difference value ΔIi and difference threshold ΔIth are compared and it is determined that the pupil is detected at a timing when difference value ΔIi exceeds difference threshold ΔIth. Then, the radius and the center coordinates of the integrating circle of this case are determined to be the radius of the pupil and the center coordinates of the pupil respectively. However, it is also applicable to consider the possibility that difference value ΔIi exceeds difference threshold ΔIth accidentally at a position other than the actual position of the pupil. In the case in which a plurality of difference values ΔIi larger than difference threshold ΔIth exist, a structure in which the radius and the center coordinate of the integrating circle corresponding to the largest difference value are determined to be the radius of the pupil and the center coordinates of the pupil is also applicable. In this arrangement, erroneous operation of the pupil detection device is prevented and the accuracy of detection of the pupil can be improved.
In this embodiment, the number of concentric integrating circles is determined to be twenty and the number of image data to be outputted from one integrating circle is determined to be eight. However, these numbers are preferably determined considering the detection accuracy, processing time, and the scale of the circuit in parallel.
According to the present invention, the pupil detection device and the iris authentication apparatus which can detect the position of the pupil at high-speed and with high degree of accuracy is provided.
As the present invention can provide the pupil detection device which can detect the position of the pupil at high-speed and with high degree of accuracy, it is effective for the iris authentication apparatus or the like which is used for personal authentication.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-206933 | Jul 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/09510 | 5/25/2005 | WO | 11/2/2005 |
