KR101179559B1 - Fingerprint Recognition Apparatus for Distinguishing Forged Fingerprint and Method therof - Google Patents

Abstract

Disclosed are a fingerprint recognition device capable of discriminating a fake fingerprint and a method of determining the same. The imitation fingerprint judgment of the present invention uses a different critical angle for total reflection when the imitation fingerprint contacts the fingerprint contact surface of the prism, and uses a fingerprint image obtained by using a separate light source whose optical axis of the emitted light has an incidence angle within a predetermined range. By comparison, it is determined whether it is a fake fingerprint.

Fingerprint reader, Optical, Imitation fingerprint, Biometric fingerprint

Description

Fingerprint Recognition Apparatus for Distinguishing Forged Fingerprint and Method therof}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fingerprint recognition device for fingerprint recognition and a method of determining the same, and more particularly, to a fingerprint recognition device capable of discriminating a fake fingerprint such as paper or film and a human bioprint.

The use of user biometric information with invariability and uniqueness for personal authentication using information devices has already been generalized. Among them, fingerprint recognition has become the most noticeable and generalized authentication means compared to other means due to its superior performance compared to a simple structure.

Normal personal authentication is mainly used in areas where security is important, such as access control, e-commerce, financial transactions, security of personal computers (PCs), and office payment systems. It is important to distinguish between fingerprints (hereinafter referred to as 'fake fingerprints') effectively.

One method of making a fake fingerprint is to contact a fingerprint reader with a liquid or a liquid such as water or oil on a paper or film on which a fingerprint image is printed. A typical fingerprint recognition device recognizes such fake fingerprints and performs false authentication.

1 is a fingerprint image obtained through a conventional fingerprint recognition device, Figure 1 (a) is a biometric fingerprint, (b) is an image obtained from the imitation fingerprint described above. It can be seen that the two images are very similar.

In addition, when the user attaches such a fingerprint to a finger, the fingerprint is distinguished by imitation fingerprint identification techniques such as a temperature measurement method, a potential measurement method, a pressure measurement method, a blood flow measurement method, and a sweat gland measurement method. Hard.

Disclosure of Invention An object of the present invention is to provide a fingerprint recognition device capable of discriminating a fake fingerprint and a human fingerprint and a method of determining the same.

Another object of the present invention is to provide a fingerprint recognition device capable of preventing an error from occurring in the process of acquiring a fingerprint image while using a separate internal light source for distinguishing and distinguishing a fake fingerprint from a human fingerprint.

In order to achieve the above object, according to the present invention, there is provided a fingerprint contact surface to which the object for fingerprint image acquisition and the exit surface for outputting the image of the fingerprint is formed, and an internal light source for fingerprint image acquisition for user authentication The fingerprint recognition device for performing user authentication includes a light source for determining a living body, at least one optical lens, an image sensor, and a fake fingerprint determination unit.

The biological judgment light source emits light having an optical axis having a predetermined angle of incidence with respect to the fingerprint contact surface. The predetermined angle of incidence is an angle greater than a first critical angle for total reflection when the refractive index of the object is 1 and smaller than a second critical angle for total reflection when a transparent liquid contacts the fingerprint contact surface.

The optical lens may form a fingerprint image emitted from the prism by the light of the light source for the biopsy, and the image sensor acquires a fingerprint image formed on the optical lens.

The imitation fingerprint determining unit calculates an area or an average gray level of the fingerprint image acquired by the image sensor. When the calculated area or average gray level of the fingerprint image is larger than a reference value, the imitation fingerprint judging unit determines the object as a biofingerprint. In such cases, it is judged as a fake fingerprint.

According to an embodiment, the imitation fingerprint determination unit may obtain the area of the fingerprint image by obtaining the number of pixels having a gray level of a predetermined reference value or more in the entire image including the acquired fingerprint image.

The predetermined angle of incidence is preferably an intermediate angle between the first critical angle and the second critical angle.

According to another embodiment, when the light emitted from the internal light source is incident through the first incident surface of the prism, and the light emitted from the biodetermination light source is incident through the second incident surface of the prism, The fingerprint recognition device may further include an opaque film formed on the second incident surface. One side of the opaque film is formed with a hole (Hole) through which the light emitted from the light source for the biological determination passes.

이하이고, 상기 생체판단용 광원의 가장자리(c")에서 상기 홀의 대향하는 가장자리(c')를 연결하는 선과 상기 생체판단용 광원의 광축이 형성하는 각이

이하인 조건을 만족하도록, 상기 홀의 크기가 정해지는 것이 바람직하다. According to an embodiment, an angle formed by a line connecting an edge b 'of the hole to an edge b' of the biodetermination light source and an optical axis of the biodetermination light source is different.

The angle formed by the line connecting the opposing edge c 'of the hole and the optical axis of the biodetermination light source at the edge c ″ of the biodetermination light source is below.

It is preferable that the size of the hole is determined so as to satisfy the following conditions.

According to another embodiment of the present invention, a method of determining a fake fingerprint of a fingerprint recognition device, which acquires a fingerprint image of an object in contact with a fingerprint contact surface of a prism and determines whether the object is a biological fingerprint or a fake fingerprint, the optical axis has a predetermined incident angle. Irradiates light having the light to the fingerprint contact surface, wherein the predetermined angle of incidence is greater than the first critical angle for total reflection when the refractive index of the object is 1, and is greater than the second critical angle for total reflection when transparent liquid contacts the fingerprint contact surface. Small imprinting step, acquiring a fingerprint image of the object formed by the irradiated light, calculating an area or average gray level of the acquired fingerprint image, and calculating the area or average gray level of the calculated fingerprint image Determining the object as a bio fingerprint when the value is larger than the value, and determining the object as a fake fingerprint when the object is small. All.

As described in detail above, the fingerprint recognition device according to the present invention can easily and effectively determine whether the fingerprint is a forged fingerprint.

The imitation fingerprint determination method of the present invention is particularly excellent for imitation fingerprints made by soaking paper or film on which a fingerprint image is printed in a transparent liquid.

In addition, the fingerprint recognition device of the present invention prevents the second incident surface from being completely exposed despite the use of a separate biological judgment light source provided outside the second entrance surface of the prism. Accordingly, by preventing the diffuse reflection in the fingerprint image acquisition process, it is possible to block the occurrence of errors in the fingerprint acquisition itself according to the provision of a separate light source.

Furthermore, the fingerprint recognition device of the present invention can further determine whether the contact fingerprint is a biometric fingerprint or a fake fingerprint by further comprising a biometric fingerprint recognition device of a separate capacitance detection method.

Hereinafter, the present invention will be described in detail with reference to the drawings.

2 is a block diagram of an optical fingerprint recognition device having a fingerprint recognition device of the present invention. The fingerprint recognition device 200 of FIG. 2 is implemented to include the fingerprint recognition device of the present invention.

Referring to FIG. 2, the fingerprint recognition device 200 includes a trapezoidal prism 210, an internal light source 231 for irradiating a fingerprint recognition light source toward the prism 210, and an optical lens for imaging image information of a fingerprint ( 233, an image sensor 235, a controller 250, and a biodetection light source 270.

Prism 210 may have a three-sided (triangular) cross-section, and may use a wider concept of optical refractors in place of the prism, but as shown in FIG. Isosceles triangles).

The prism 210 of FIG. 2 includes a fingerprint contact surface 210a to which a fingerprint is in contact, an emission surface 210b at which light (fingerprint image) reflected or scattered from the fingerprint contact surface 210a is emitted, and an internal light source 231. The first incident surface 210c, to which the emitted light is incident, and the second incident surface 210d, to which the light emitted from the biopsy light source 270 is incident, are provided.

First, the basic fingerprint recognition process of the optical fingerprint recognition device 100 of FIG. 2 is as follows. When the user touches the finger on the fingerprint contact surface 210a, the light irradiated from the internal light source 231 passes through the first entrance surface 210c, the fingerprint contact surface 210a, and the exit surface 210b of the prism 210. An image is formed on the optical lens 233 and input to the image sensor 235. In the scattered fingerprint recognition device 200 as shown in FIG. 2, the light emitted from the internal light source 231 is incident on the fingerprint contact surface 210a at an angle smaller than the critical angle for perpendicular or total reflection. The light emitted from the internal light source 231 passes or scatters along the valleys and ridges of the fingerprint in contact with the fingerprint contact surface 210a to form a fingerprint image. The image sensor 235 obtains an image of the fingerprint in contact with the fingerprint contact surface 210a by outputting a digital fingerprint image signal, which is an electrical signal corresponding to the incident fingerprint image.

However, since the imitation fingerprint judgment of the present invention is implemented by another distinct mechanism different from the fingerprint recognition mechanism, the fingerprint recognition device 200 applied to the present invention is not limited to the scattering expression shown in FIG. 2. Therefore, as described above, the prism 210 is not limited in its cross-sectional shape, such as trapezoid or triangle, and the position of the internal light source 231 is provided at various positions according to the fingerprint recognition method and the shape of the prism 210. Can be.

The controller 250 controls the overall operation of the fingerprint recognition device 200 including acquiring a fingerprint image.

In addition, the controller 250 includes a fake fingerprint determination unit 251 to determine whether the fingerprint contacted to the fingerprint contact surface 210a is a biometric fingerprint or a fake fingerprint.

After the imitation fingerprint determination unit 251 turns on the biodetection light source 270, the fingerprint contact surface based on the digital fingerprint image signal input from the image sensor 235 through the prism 210 and the optical lens 233. It is determined whether the fingerprint in contact with 210a is a fake fingerprint. At this time, the internal light source 231 is controlled to be in an off state.

The biological judgment light source 270 irradiates the light for distinguishing the dummy fingerprint to the fingerprint contact surface 210a through the second incident surface 210d. The biological determination light source 270 preferably uses a light source having a predetermined viewing angle (for example, about 30 °) around the optical axis of the light source.

The light emitted from the biopsy light source 270 to the fingerprint contact surface 210a is totally reflected, absorbed or refracted, and is then imaged on the optical lens 233 through the exit surface and input to the image sensor 235.

At this time, when the incident angle of the optical axis irradiated from the biometric light source 270 to the fingerprint contact surface 210a is within a predetermined range, the amount of light incident on the image sensor 235 is in contact with the fingerprint contact surface 210a ( Biometric fingerprint or imitation fingerprint). In other words, the area of the image acquired by the image sensor 235 using the biometric light source 270 varies according to the type of the fingerprint in contact with the fingerprint contact surface 210a. The operation of the biometric light source 270 and the determination of the dummy fingerprint will be described again below.

In the above, the fingerprint recognition device 200 of FIG. 2 is implemented to use the prism 210, the optical lens 233, and the image sensor 235 in common for acquiring a fingerprint image and determining a fake fingerprint. However, according to the difference in the fingerprint recognition method, the fingerprint recognition device 200 may be provided with a separate optical lens and an image sensor for obtaining a fingerprint image using the biometric light source 270.

In addition, according to another embodiment, it may be implemented as an independent imitation fingerprint device that does not include the internal light source 231 and determines only whether the fingerprint contacted to the fingerprint contact surface 210a is a bio fingerprint or a fake fingerprint.

Hereinafter, a method of determining the imitation fingerprint using the biopsy light source 270 will be described in more detail.

3 is a view provided to explain the method of determining the imitation fingerprint.

When the refractive index of the prism 210 is n ₁ and the refractive index of the medium in contact with the fingerprint contact surface 210a of the prism 210 is n ₂ , the imitation fingerprint determination method of the present invention contacts the fingerprint contact surface 210a. The critical angle for total reflection at the fingerprint contact surface 210a varies depending on the type of fingerprint (bioprint or fake fingerprint).

When light is irradiated from a medium having a large refractive index to a medium having a small refractive index, the incident light is refracted if the incident angle is less than or equal to the critical angle, and totally reflected if it is greater than or equal to the critical angle. The critical angle is determined by the refractive indices of the two media forming the interface.

3A illustrates a case where there is no contact with the fingerprint contact surface 210a, and the refractive index n ₂ is 1, which is the refractive index of air. In addition, hereinafter, it is assumed that the refractive index n ₁ of the prism 210 is 1.6 for convenience of explanation.

Snell's law for calculating the critical angle for total reflection is as shown in Equation 1 below.

Here, θ ₁ is the angle of incidence and θ ₂ is the angle of refraction. Θ ₂ for total reflection is 90 °.

When n ₁ = 1.6, n ₂ = 1 (refractive index of air) and θ ₂ = 90 ° are applied to Equation 1, a critical angle for total reflection when there is no contact with the fingerprint contact surface 210a (hereinafter, referred to as 'first critical angle') Θ _min is obtained as follows.

1.6 × sinθ _min = 1.0 × sin90 °

θ _min = sin ^-1 (1 / 1.6) ≒ 39 °

Therefore, when the incident angle θ _i of the light irradiated from the biometric light source 270 to the fingerprint contact surface is smaller than the first critical angle θ _min , the amount of light refracted by the fingerprint contact surface 210a and incident on the image sensor 235 is remarkably given. When the incident angle θ _i is greater than the first critical angle θ _min , most of the light emitted from the biopsy light source 270 is totally reflected at the fingerprint contact surface 210a to reach the image sensor 235.

3B illustrates a case where the dummy fingerprint 310 contacts the fingerprint contact surface 210a. Here, the imitation fingerprint 310 is soaked or soaked in a transparent liquid such as water or oil on the paper or film (Film) on which the fingerprint image is printed. Hereinafter, assuming that the transparent liquid is water (refractive index 1.33), the critical angle (hereinafter referred to as 'second critical angle') θ _max for total reflection when the dummy fingerprint 310 is contacted is obtained as follows.

1.6 × sinθ _max = 1.33 × sin90 °

θ _max = sin ^-1 (1.33 / 1.6) ≒ 56 °

Therefore, when the incident angle θ _i of the light irradiated from the biopsy light source 270 to the fingerprint contact surface is smaller than the second critical angle θ _max , the incident angle θ _i is refracted by the fingerprint contact surface 210 a, and when the incident angle θ _i is larger than the second critical angle θ _max , the fingerprint contact surface is present. Total reflection at 210a reaches the image sensor 235.

At this time, since the transparent liquid constituting the imitation fingerprint is in contact with most of the fingerprint contact surface 210a, the optical characteristics caused by the imitation fingerprint are ignored and are optically identical by the liquid. As a result, the light incident at the incident angle θ _i smaller than the second critical angle θ _max is mostly refracted, and the amount of light incident on the image sensor 235 is very small.

The second critical angle with respect to the determination of θ _max, based on the low-refractive index of the transparent liquid (water, alcohols, etc.) that can be used in the artificial fingerprint is preferable to set the second critical angle θ _max. It is desirable to base the water on its refractive index, which is smaller than other liquids, and is usually the simplest and most commonly used.

Based on the above description, the case where the incident angle θ _i of the light emitted from the biopsy light source 270 is set as in Equation 2 below will be described.

Based on these conditions, in the case of the biofingerprint, total reflection may occur in the bone on the fingerprint, whereas in the case of the imitation fingerprint, the possibility of total reflection is significantly reduced, so that the amount of light incident on the image sensor 235 is input to the biofingerprint and the imitation fingerprint. Depends on. Therefore, based on Equation 2, it is possible to distinguish whether the fingerprint in contact with the fingerprint contact surface 210a is a biometric fingerprint or a fake fingerprint.

Here, since the incident angle θ _i refers to the incident angle formed by the optical axis of the light emitted from the biodetection light source 270 to the fingerprint contact surface 210a, the incident angle θ _i of the light emitted from the biodetection light source 270 is used for the biological judgment. The attitude of the light source 270 is determined. That is, the angle of incidence formed by the optical axis of the light emitted from the biopsy light source 270 should be provided to satisfy Equation 2 above. However, there is no limitation on the point where the optical axis of the biopsy light source 270 meets the fingerprint contact surface 210a, but the center of the fingerprint contact surface 210a is preferable.

Referring to FIG. 2, the biological judgment light source 270 provided on the outside of the second incident surface 210d is provided to irradiate light for distinguishing the imitation fingerprint toward the fingerprint contact surface 210a, and the biological judgment light source 270. The angle of incidence formed at the center of the fingerprint contact surface 210a by the optical axis of the light emitted from the?

Therefore, when using the imitation fingerprint 310 soaked in water, the incident angle of the biopsy light source 270 may be 39 ° ≤ θ _i ≤ 56 °, it is most preferable to set the middle angle of 48 ° Do.

FIG. 4 is a diagram illustrating an image acquired by using the biodetection light source, and includes a fingerprint image as a whole image received from the image sensor 235 using the biodetection light source 270. Hereinafter, with reference to FIGS. 2 and 4, when the light emitted from the biodetection light source 270 is incident on the fingerprint contact surface 210a at an incident angle of 48 °, an image obtained by the image sensor 235 will be described.

When the bio fingerprint is in contact with the fingerprint contact surface (210a), the path of the light emitted from the bio-judgment light source 270 depends on the bone and ridge of the bio fingerprint. Since the part where the bone of the biofingerprint is in contact does not have any contact (first critical angle θ _min ), the incident angle of the light emitted from the biological judgment light source 270 is greater than the first critical angle θ _min so that the total reflection Occurs. Light irradiated to the contact area of the ridge of the bio fingerprint is absorbed or scattered.

However, since a general light source is emitted with a viewing angle of about 30 ° with respect to the optical axis, total reflection is not all performed at the contact surface of the bone of the fingerprint. Therefore, the image acquired by the image sensor 235 may not be a fingerprint image that can be properly recognized, and FIG. 4A is an example.

When the dummy fingerprint is in contact with the fingerprint contact surface 210a, the critical angle applied to the fingerprint contact surface becomes the second critical angle θ _max . Since the incident angle of the light emitted from the biopsy light source 270 is smaller than the second critical angle θ _max , refraction occurs throughout the fingerprint contact surface 210a. Therefore, the amount of light incident on the image sensor 235 becomes very small, and the image obtained by the image sensor 235 is as shown in FIG.

Comparing (a) and (b) of Figure 4, it can be seen that the area of the portion (black portion) where the fingerprint image is obtained is significantly different. The images of (a) and (b) are inverted of the entire image received from the image sensor 235. In fact, the fingerprint image incident on the optical lens 233 and the image sensor 235 corresponds to the part where the actual light is incident, and thus appears brighter than other parts.

The fingerprint recognition device 200 determines whether the fingerprint contacted to the fingerprint contact surface 210a is a fake fingerprint or a bioprint based on the fingerprint image.

On the other hand, as shown in Figure 2, when the internal light source 231 and the biodetermination light source 270 is incident to the prism 210 through a different surface, the following additional considerations may be necessary.

First, the fingerprint acquisition light emitted from the internal light source 231 and incident through the first entrance surface 210c may cause diffuse reflection by the transparent second entrance surface 210d, so that the fingerprint shape may not be obtained. Is that there is.

To solve this problem, the fingerprint recognition device of the present invention may further include an opaque film 211 formed on the second incident surface 210d of the prism 210 as shown in FIG. However, in the opaque film 211, a hole 213 for passing light emitted from the second incident surface 210d must be formed.

The second consideration is that, since the light emitted from the biopsy light source 270 is emitted with a viewing angle of about 30 °, some of the light incident on the fingerprint contact surface 210a of the biopsy light source 270 is It has an angle of incidence greater than θ _max or less than θ _min , which does not contribute to biofingerprint judgment.

5 is a view showing a prism according to another embodiment of the present invention, (a) is a cross-sectional view thereof, and (b) is a view of the prism seen from the biodetection light source 270. Referring to FIG. 5, the biodetection light source 270 is provided outside the second incident surface 210d of the prism 210, and the optical axis thereof is directed toward the center a of the fingerprint contact surface 210a of the prism 210. have.

In the drawing, the angle of incidence of the light of the biometric light source 270 increases as the center of the fingerprint contact surface 210a moves from b to b, and decreases as it moves from a to c. The incident angle at point b becomes θ _max , and beyond the point b, the angle of incidence is greater than θ _max . Light having an angle of incidence greater than θ _max does not satisfy Equation 2, resulting in meaningless light. On the contrary, the incidence angle at point c becomes θ _min and if it exceeds c, it has an incidence angle smaller than θ _min . Light having an angle of incidence greater than θ _min does not satisfy Equation 2, which is also meaningless light.

On the other hand, the biofingerprint determination process to be described below is made based on the size (eg, A of FIG. 4) of the image area obtainable through the biodetection light source 270. Therefore, the length from b to c, which is arbitrarily determined by the user, is related to the size of such biofingerprint determination image. In addition, the length between b and c, the length between a and b or the length between a and c affects the position of the biodetection light source 270.

In order to solve the second consideration, it is necessary to adjust the size of the hole 213 formed in the opaque film 211 so that the angle of incidence of the light emitted from the biopsy light source 270 satisfies Equation 2.

Therefore, the distance between a-b and a-c is determined by the user, and a criterion is derived that the incident angle at point b should be determined as θ _max , and the incident angle at point c as θ _min .

If so, the length of the hole 213 extends from the point b to the incident angle θ _max to meet the second incidence surface 210d, and the length of the hole 213 extends from the c to the incident angle θ _min to the second incident surface 210d. It may be the distance between the meeting point (c '). The shape of the hole 213 may be circular or rectangular.

Here, since the distance between a-b and a-c is an arbitrary designation, the above relationship is summarized as follows based on the biodetection light source 270.

The angle formed by the line connecting the edge of the corresponding hole 213 at the edge of the biodetection light source 270 and the optical axis of the biodetection light source 270 is expressed by Equations 3 and 4 below.

Here, Equation 3 is an angle formed by a line connecting the b 'of the hole 213 at the edge b "of the biodetermination light source 270 and the optical axis of the biodetermination light source 270, and Equation 4 is a biodetermination Corresponds to an angle formed by a line connecting c 'of the hole 213 at the edge c ″ of the molten light source 270 and the optical axis of the biodetection light source 270. θ _i refers to a specific incident angle satisfying Equation 2 at the center a of the fingerprint contact surface 210a.

이하이고, 생체판단용광원(270)의 가장자리 c"에서 홀(213)의 c'를 연결하는 선과 생체판단용광원(270)의 광축이 형성하는 각이

이하인 조건을 만족하도록 정해지는 것이 바람직하다. As a result, if the position of the biodetection light source 270 provided outside the prism 210 is fixed such that the optical axis has a specific angle of incidence that satisfies Equation 2, the size of the hole 213 is the biodetection light source. The angle formed by the line connecting b 'of the hole 213 at the edge b "of 270 and the optical axis of the biodetection light source 270 is formed.

The angle formed by the line connecting c 'of the hole 213 and the optical axis of the biodetection light source 270 at the edge c "of the biodetection light source 270 is as follows.

It is preferable to be determined so as to satisfy the following conditions.

Hereinafter, a method for determining whether the fingerprint is imitation using the image of FIG. 4 will be described based on the operation of the imitation fingerprint determination unit 251.

On the basis of the image inputted from the image sensor 235 by the imitation fingerprint determining unit 251, a method of determining whether the fingerprint contacted to the fingerprint contact surface 210a is a imitation fingerprint is the size of the acquired fingerprint image (or Information derived corresponding to size).

As an example, since the area of the fingerprint image acquired by the image sensor 235 is different for the biometric fingerprint and the dummy fingerprint, there is a method of determining that the fingerprint is a fake fingerprint when the area of the acquired fingerprint image is smaller than a predetermined reference area.

6 is a view for explaining an example of the imitation fingerprint determination method of the present invention.

The imitation fingerprint determination unit 251 outputs a predetermined control signal when the fingerprint is in contact with the fingerprint contact surface 210a so that the biodetection light source 270 is turned on (S601), and then the fingerprint through the image sensor 235. The entire image including the image is received (S603).

The imitation fingerprint determination unit 251 calculates the area of the fingerprint image among the entire images. The calculation of the area may be performed by obtaining a number of pixels whose gray level of the pixel is larger than a threshold level (which may be different from the previous reference level and determining whether there is an image). S605).

The imitation fingerprint determination unit 251 determines whether the area of the fingerprint image calculated in step S605 is larger than the reference area. Here, the reference area corresponds to a value for distinguishing the area of the fingerprint image at the time of the bio fingerprint and the area of the fingerprint image at the time of imitation fingerprint based on FIG. 4, and can be obtained experimentally (S607).

As a result of the determination in step S607, the imitation fingerprint determination unit 251 determines that the fingerprint is biometric fingerprint if the area of the fingerprint image is larger than the reference area (S609), if it is smaller than the reference area (S611).

According to an embodiment, the imitation fingerprint determination unit 251 determines whether the fingerprint image acquired in the range of the predetermined area (the area range of the fingerprint image corresponding to the biometric fingerprint) corresponds to the determination method of steps S607 to S611. You can also determine whether the fingerprint is fake.

The difference in the area of the acquired fingerprint image corresponds to the difference in the average gray level obtained for the entire image or a portion of the entire image. Therefore, there is a method of determining the gray level of the entire image (or a portion thereof) input from the image sensor 235 and determining the fake fingerprint when the gray level is smaller than the reference level.

In the case of obtaining the average gray level for a part of the entire image, it is preferable to apply an area (for example, A of FIG. 4) larger than the normal area of the fingerprint image obtained by an imitation fingerprint obtained experimentally.

However, depending on whether the entire image input from the image sensor 235 is inverted, a fingerprint image having an average gray level larger than a reference level may be determined as a fake fingerprint.

7 is a view for explaining another example of the imitation fingerprint determination method of the present invention.

The imitation fingerprint determination unit 251 outputs a predetermined control signal when the fingerprint is in contact with the fingerprint contact surface 210a so that the biodetection light source 270 is turned on (S701) and the fingerprint image through the image sensor 235. The entire image including the input is received (S703).

The imitation fingerprint determination unit 251 calculates an average gray level of a predetermined portion (eg, A of FIG. 4) of the entire image (S705), and compares the calculated average gray level with a reference value (S707).

As a result of the comparison in step S707, the imitation fingerprint determining unit 251 determines that the fingerprint is a biometric fingerprint when the average gray level is greater than the reference value (S709), and determines that the imitation fingerprint is smaller than the reference value (S711).

In the above manner, the fake fingerprint determination unit 251 may determine whether the obtained fingerprint image is due to the fake fingerprint.

The fingerprint recognition device 200 of the present invention may further apply a non-contact capacitive method to determine whether the fingerprint in contact with the fingerprint contact surface 210a is a bio fingerprint.

To this end, the fingerprint recognition device 200 may further include a conductor terminal installed inside or adjacent to the outside of the prism 210 and a biometric part.

The biometric part allows capacitance to be formed between the conductor terminal and the ground, and detects a change in capacitance caused by the fingerprint contacting the fingerprint contact surface 210a of the prism 210 to determine whether the contact fingerprint is a bio fingerprint. can do.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. It will be understood by those skilled 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.

1 is a fingerprint image obtained through a conventional fingerprint recognition device,

2 is a block diagram of an optical fingerprint recognition device having a fingerprint recognition device of the present invention;

3 is a view provided for the description of the fake fingerprint determination method;

4 is a view showing an image obtained using the biodetection light source of FIG.

5 is a view showing a prism according to another embodiment of the present invention;

6 is a view for explaining an example of the imitation fingerprint determination method of the present invention, and

7 is a view for explaining another example of the imitation fingerprint determination method of the present invention.

Claims (12)

In the fingerprint recognition method of the fingerprint recognition device for acquiring a fingerprint image of an object in contact with the fingerprint contact surface of the prism to determine whether the object is a bio fingerprint or a fake fingerprint, Irradiate the fingerprint contact surface with the bio-fingerprint judging light having an optical axis having a predetermined angle of incidence, wherein the predetermined angle of incidence is larger than a first critical angle for total reflection when the refractive index of the object is 1, and a transparent liquid contacts the fingerprint surface. A first step of marking an angle smaller than the second critical angle for total reflection of the case; A second step of acquiring a fingerprint image of the object formed by the biometric fingerprint light irradiated onto the fingerprint contact surface; And A third step of calculating an area or an average gray level of the acquired fingerprint image; When the calculated area or the average gray level of the fingerprint image is greater than the reference value comprises the fourth step of determining the object as a bio fingerprint, and when it is small as a dummy fingerprint, When the light for acquiring the fingerprint image for user authentication is incident through the first incident surface of the prism and the bio-fingerprint determination light is incident through the second incident surface of the prism, separately from the light for determining the fingerprint An opaque film having a hole formed on one side is formed on the second incidence surface, and the light for determining the bio fingerprint in the first step is incident through the hole formed in the opaque film. Way. The method of claim 1, The third step, And determining the area of the fingerprint image by obtaining the number of pixels having a gray level equal to or greater than a reference level for determining whether there is a fingerprint image in the entire image including the fingerprint image. The method of claim 1, And the second threshold angle corresponds to a case where the transparent liquid is water. 4. The method according to any one of claims 1 to 3, And the predetermined incident angle is an intermediate angle between the first critical angle and the second critical angle. delete The method of claim 1, The size of the hole, The angle formed by the line connecting the opposing edge b 'of the hole and the optical axis of the light source is smaller than the difference between the second critical angle and the incident angle at the edge b ″ of the light source for emitting the biofingerprint determination light. Equals or equals The angle formed by the line connecting the opposing edge c 'of the hole to the edge c' of the light source for emitting the biofingerprint light and the optical axis of the light source is smaller than the difference between the incident angle and the first critical angle. Or a fake fingerprint determination method characterized in that it is determined to satisfy the same conditions. In the fingerprint recognition device for performing user authentication with a prism formed with a fingerprint contact surface to which the object for the fingerprint image is contacted, an exit surface for outputting the image of the fingerprint, and an internal light source for obtaining a fingerprint image for user authentication , Total reflection when the optical axis emits light having a predetermined angle of incidence with respect to the fingerprint contact surface, wherein the predetermined angle of incidence is greater than a first critical angle for total reflection when the refractive index of the object is 1 A light source for biodetermining an angle smaller than a second critical angle for a; At least one optical lens provided adjacent to the exit surface to form a fingerprint image emitted from the prism by light from the light source for the biological determination; An image sensor which acquires a fingerprint image formed on the optical lens; And The area or average gray level of the fingerprint image acquired by the image sensor is calculated, and when the calculated area or average gray level of the fingerprint image is larger than the reference value, the object is determined as a biometric fingerprint, and when the size is small, the imitation fingerprint is determined. Imitation fingerprint judgment to include; When the light emitted from the internal light source is incident through the first incident surface of the prism, and the light emitted from the biopsy light source is incident through the second incident surface of the prism, the light is incident on the second incident surface. A fingerprint recognition device, characterized in that it further comprises an opaque film formed on one side and the hole (Hole) through which the light emitted from the light source for the bio-detection passes through to prevent diffuse reflection when acquiring the fingerprint image for the user authentication. The method of claim 7, wherein The imitation fingerprint judgment portion, Fingerprint recognition device, characterized in that to obtain the area of the fingerprint image by obtaining the number of pixels having a gray level or more than a reference level for determining whether there is a fingerprint image in the entire image including the fingerprint image. The method of claim 7, wherein And the second critical angle corresponds to a case where the transparent liquid is water. The method according to any one of claims 7 to 9, The predetermined incident angle is a fingerprint recognition device, characterized in that the intermediate angle between the first critical angle and the second critical angle. delete The method of claim 7, wherein The size of the hole, The angle formed by the line connecting the opposing edge b 'of the hole and the optical axis of the light source is smaller than or equal to the difference between the second critical angle and the incident angle at the edge b ″ of the biodeterminant light source, The angle formed by the line connecting the opposing edge c 'of the hole to the edge c' of the light source for emitting the biofingerprint light and the optical axis of the light source is smaller than the difference between the incident angle and the first critical angle. Or a fingerprint recognition device, characterized in that determined to satisfy the same conditions.

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