WO2004081852A1

WO2004081852A1 - Information terminal with fingerprint image acquisition device

Info

Publication number: WO2004081852A1
Application number: PCT/KR2004/000546
Authority: WO
Inventors: Soonwon Jung; Sunghyu Shin
Original assignee: Nitgen Co. Ltd.
Priority date: 2003-03-14
Filing date: 2004-03-15
Publication date: 2004-09-23

Abstract

In this invention, it is not necessary for a user to closely contact his fingerprint on a fingerprint-reading window to obtain the fingerprint image, fingerprint authentication can be achieved in any situation, without enlarging the size of a camera-mounted mobile phone. This invention comprises an image-sensing means for converting image to an electrical signal; a mode selection means for letting a user select a mode of common object photographing or a mode of fingerprint photographing; a lens means for functioning as a wide-angle lens that photographs a common object image when a user selects a mode of common object photographing, and for functioning as a close-up lens that photographs a fingerprint image when a user selects a mode of fingerprint photographing; a storage means for storing image data output from the image-sensing means; and a sending means for sending the image data output from the image-sensing means to the exterior.

Description

INFORMATION TERMINAL WITH FINGERPRINT IMAGE ACQUISITION DEVICE

Technical Field

The present invention relates to a fingerprint image acquisition device for acquiring fingerprint image by taking a photograph from a fingerprint surface by means of a mobile telephone, PDA, or the like.

Background Art

A fingerprint acquisition device can be utilized in a wide scale as a device for comparing and recognizing fingerprints between an acquired fingerprint and a pre- registered fingerprint of a user, in the form of a locking device at a door or a safe, access control to a gate, attendance control of employees, access control to a computer, etc. The fingerprint acquisition apparatuses or devices for performing such fingerprint recognition are generally classified into two types: an optical type and a non-optical type. The optical type fingerprint acquisition device is a device that illuminates a light to a fingerprint laid on a prism, interprets a fingerprint image reflected according to the shapes of valleys or ridges of the fingerprint and formed on an image sensor, and compares the interpreted image with a pre-stored fingerprint. A typical optical fingerprint acquisition device is shown in Fig. 1. Fig. 1 is a schematic diagram illustrating an operational principle of a fingerprint acquisition device of a so-called "scattering type."

The fingerprint acquisition device in Fig. 1 comprises an image prism 1, a backlight 3, a lens 4, and an image sensor 5. Here, the light is incident on the imaging surface 2 of the prism 3 from the backlight 3 at an angle far smaller than the right angle or a critical angle. Therefore, the light illuminating the valleys of the fingerprint not in contact with the imaging surface 2 penetrates the imaging surface 2 and does not reach the image sensor 5. On the other hand, the light illuminating the ridges of the fingerprint is scattered by the ridges. The scattered light is incident on the lens 4, and is focused on a surface of the image sensor 5. Accordingly, the amounts of light incident on the image sensor 5 differ from the valleys to the ridges, and as a consequence, the image sensor 5 outputs electric signals of different levels depending on a pattern of a fingerprint. An image processor (not shown) formulates the output values of the image sensor 5 into the digital signals so as to recognize a fingerprint pattern by a pre-described algorithm.

In a conventional fingerprint acquisition device exemplified in Fig. 1, a fingerprint must be closely contacted the imaging surface 2 of the prism 1 in order to obtain a clearer fingerprint image. For example, when the fingerprint acquisition device shown in Fig. 1 is built in a housing which is to be installed at a door, a computer, etc. and the imaging surface thereof is exposed to the exterior, a user must closely touch his fingerprint on an imaging surface or fingerprint reading window to have authentication be reliably performed.

Recently, according to the development of digital camera technology, a miniaturized digital camera has been mounted on information terminals, such as mobile telephones or PDAs. This provides the information terminal with a lens and an image-detecting device such that the photograph taken from the objects may be stored in a memory in the terminal or sent to other's terminal. Typically, since this kind of digital camera that is included in an information terminal uses a wide-angle lens of which the focal length is fixed at infinity, the digital camera cannot provide a function of close-up photographing.

Disclosure of Invention

This invention has been developed to avoid the drawbacks of the conventional art that a fingerprint image could be acquired when a fingerprint must contact the fingerprint reading window. On a certain occasion, there may be necessity of acquiring fingerprint image from a finger placed apart from the fingerprint-reading window. For example, there is the possibility of not touching one's fingerprint on a fingerprint reading window in accordance with spatial limitation. In addition, the latent fingerprint remaining after a fingerprint contacts a fingerprint reading window causes the authentication performance to commit an error, and for avoiding this, the complicated fingerprint authentication algorithm is required. Additionally, in the case of fingerprint authentication for payment in a camera-mounted information terminal which is being popularized recently, adding a fingerprint image acquisition device along with a camera to an information terminal goes against the stream of product miniaturization.

Therefore it is an object of the present invention to provide an information terminal for acquiring fingerprint image by taking a photograph from a fingerprint surface apart from a lens of a camera-mounted information terminal, in which provides the lens with close-up function without any inordinate modification of the terminal configuration. Basically, the concept of this invention is that fingerprint image is acquired by photographing a fingerprint using a camera. In a conventional fingerprint acquisition device, only if a fingerprint contacts a fingerprint-reading window that is one of the faces of an imaging prism (see Fig. 1), fingerprint acquisition is possible by using an optical mechanism. To the contrary, the present invention provides a fingerprint acquisition device that acquires fingerprint image by taking a photograph from a distantly placed fingerprint by means of a close-up optical system of a camera.

In a camera, a generally used wide-angle lens is designed to have minimum aberration when photographing an infinitely distanced object. In other words, a lens is designed under the assumption that the light incident to a lens is a bundle of parallel beams. Since the above assumption may deviate from a standard photographing condition, a lens is sometimes designed with reference to a distance that is 50 times farther than a focal length of the lens (e.g., approximately 2.5m for a lens whose focal length is 50mm). However, since the performance of a lens deteriorates as the condition deviates from a design standard, if a generally used wide-angle lens is used for photographing closely located objects, the photographed image becomes poor in quality. To overcome this drawback, a close-up lens or macro lens is used. The close-up lens is a lens whose focal length is designed such that the dimension of the photographed image is approximately 1/10 of the actual object (e.g., approximately 60cm for a lens whose focal length is 50mm). By using the close-up lens, clear and high-magnified image can be obtained from a closely placed object that is distanced 7 to 8cm far. Also the close-up lens may be used to 1 : 1 equal-size photographing.

Referring to the close-up function of a camera, a fingerprint acquisition device according to the present invention will be described.

Fig. 2 shows conceptual configuration of a fingerprint acquisition device according to the present invention. In construction, it is composed of an image- sensing element 21 that has an image receiving window and a lens assembly 23 for focusing a fingerprint 20 on the image-receiving window of the image-sensing element 21.

Configuration shown in Fig. 2 may be implemented by a camera mounted in an information terminal, such as a mobile phone, etc. By adding a function of fingerprint image acquisition to a camera-mounted information terminal can be simply achieved because it is possible to utilize the ready-installed camera construction. That is, by adding a function of close-up photographing to a miniaturized camera mounted in a terminal, a common object as well as a fingerprint can be acquired.

In order to apply the Fig. 2 configuration to an information terminal, a close- up lens should be used as the lens assembly 23. Since there is a close-up lens capable of photographing an object distanced merely several millimeters, the close- up lens may be optimally adapted to this invention. However, it is more preferable that the lens assembly 23 is selectable between a close-up lens and a wide-angle lens to photograph a fingerprint as well as common objects.

In addition, as shown in Fig. 3, a finger support 25 may be further included to maintain a regular interval between a lens assembly 23 and a finger 20. This finger support 25 plays a role in acquiring clearer fingerprint image by preventing the finger from trembling. The finger support 25 lets a finger be positioned at a distance of "d" from the lens assembly 23. In addition, as shown in Fig. 4, the fingerprint acquisition device may further comprise a lighting means 27 for illuminating a fingerprint surface to obtain a clearer fingerprint image. For the lighting means 27, an infrared LED may be used, which is invisible to the human eyes, but the image-sensing element can detect it.

Hereafter, the preferred embodiments to cany out those technical ideas of the information terminal according to the present invention will be described.

Brief Description of the Drawings

The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which:

Fig. 1 shows a conventional optical fingerprint image acquisition device,

Figs. 2 to 4 show the schematics explaining fundamentals of the present invention, Figs. 5 and 6 exemplify a conventional camera-mounted mobile telephone,

Figs. 7 and 8 show how to use a mobile telephone with a fingerprint acquisition device according to one embodiment of the present invention,

Figs. 9 to 12 exemplify how to select a wide-angle lens or a close-up lens in a mobile telephone with a fingerprint acquisition device according to one embodiment of the present invention,

Figs. 15 and 16 exemplify one embodiment of a finger support of the present invention,

Figs. 18 to 21 exemplify a variety of embodiments of a lighting means of the present invention, and

Figs. 22 to 25 show images resulted from each stage of the process for extracting fingerprint data from the fingerprint image acquired by a fingerprint acquisition device according to the present invention.

Preferred Embodiments for Carrying out the Invention

Figs. 5 and 6 show the examples of camera-mounted mobile phones currently on the market. In Fig. 5, a separate camera unit 101 is attached to the side of a mobile phone. In Fig. 6, a camera is built in the body of a mobile phone. A camera lens 103 and 105 is illustrated in the both drawings. From the foregoing, these camera lenses 103 and 105 are, of course, wide-angle lenses, each of which the focal length is fixed to the infinite distance (typically 3 to 5 meters).

Although there are various types of camera-mounted mobile phone in addition to those shown in Figs. 5 and 6, the embodiment of the present invention will be described mainly regarding the one shown in Fig. 6. However, the scope of the present invention is applicable to any type of mobile phone by those who ordinarily skilled in the art. This will be apparent from the following detailed description.

If the function of fingerprint acquisition is added to a camera-mounted mobile phone according to the present invention, a user places his or her fingerprint 109 in front of a camera lens 107 which includes a close-up function to provide the fingerprint to a fingerprint acquisition device, as shown in Fig. 7.

In the mobile phone having a function of fingerprint acquisition includes a mode selection function 110 by which a user may select common object photographing or fingerprint image photographing (see Fig. 8). If a user selects a mode of common object photographing 111, the object is photographed by a wide- angle lens and the photographed image data is stored in built-in memory or transferred to another mobile phone or PC. On the other hand, in a mode of fingerprint acquisition, a camera lens 107 is changed to a close-up lens, and the fingerprint is photographed by the close-up lens. The acquired fingerprint may be stored in a built-in memory, sent to another mobile phone or fingerprint authentication server according to the pre-described mobile communication protocol, or sent to PC through USB.

From the foregoing, the present invention, an information terminal with a fingerprint acquisition device comprises an image-sensing means for converting image to an electrical signal; a mode selection means for letting a user select a mode of common object photographing or a mode of fingerprint photographing; a lens means for functioning as a wide-angle lens that photographs a common object image when a user selects a mode of common object photographing, and for functioning as a close-up lens that photographs a fingerprint image when a user selects a mode of fingerprint photographing; a storage means for storing image data output from the image-sensing means; and a sending means for sending the image data output from the image-sensing means to the exterior.

Repeatedly, in accordance with the present invention, since a fingerprint image can be acquired by using close-up function as shown in Figs. 7 and 8, the conventional optical fingerprint image acquisition device different from a camera in construction can be space-efficiently built in a mobile phone. In addition, since it is not necessaiy for a user to closely contact his fingerprint on a fingerprint-reading window, the fingerprint can be acquired in normal phone-using pose and a latent fingerprint does not stay on the fingerprint-reading window.

Here, in order to implement both a mode of common object photographing and a mode of fingerprint photographing in a mobile telephone, a user must be able to easily switch a camera lens between a wide-angle lens and a close-up lens. Figs. 9 to 14 show the ways of selecting a close-up lens for photographing a fingerprint while using a wide-angle lens in normal times, i.e., when photographing common objects.

As one example, Figs. 9 and 10 show that a secondaiy lens is overlapped on a conventional camera lens. A primaiy lens 115 held by a primaiy lens holder 117 is mounted in a body of mobile phone, and a secondary lens holder 121 holding a secondaiy lens 119 is pivotally installed centering around a pivot pin 123 adjacent to the primaiy lens holder 117. Fig. 9 shows a case that a user selects a mode of common object photographing that the primaiy lens 115 is used as a wide-angle lens. To change a mode to that of fingerprint photographing, a user can rotate the secondaiy lens holder 121 and overlap it on the primary lens holder 117, as shown in Fig. 10. Then the primaiy lens 115 and the secondary lens 119 cooperate to function close-up photographing.

Figs. 11 and 12 show another example of overlapping a secondaiy lens on the conventional lens. A primary lens 115 held in a primary lens holder 117 is mounted in a body of mobile phone 125, and a secondary lens holder 127 holding a secondaiy lens 119 is installed slidably against the body 125, adjoining the primary lens holder 117. To photograph a common object, a user can push a knob 129 of the secondary lens holder 127 to put it away from the primaiy lens holder 117 such that the secondaiy lens 119 is not overlapped on the primaiy lens 115 (see Fig. 11). To photograph a fingerprint, a user can reversely push a knob 129 of the secondaiy lens holder 127 to overlap the secondary lens 119 on the primaiy lens 115 (see Fig. 12). Then the primary lens 115 and the secondaiy lens 119 cooperate to function close-up photographing.

Figs. 13 and 14 show yet another example of overlapping a secondaiy lens on the conventional lens, which has a structure similar to a zoom lens of a camera. A primaiy lens 115 is mounted on a body of mobile phone 125, and a secondaiy lens 119 is installed in front of a primaiy lens 115, the secondary lens 119 moving back and forth against the primaiy lens 115 to adjust the distance between the lenses. In the case of selecting a mode for photographing a common object, the secondaiy lens 119 moves proximally to the primaiy lens 115, and the lenses function as a wide- angle lens for photographing common objects (see Fig. 13). In the case of a mode for photographing a fingerprint, the secondaiy lens 119 moves away from the primary lens 115, and the two lenses function as a close-up lens for photographing a fingerprint (see Fig. 14). In those three examples, rotation or reciprocal movement of the secondaiy lens may be achieved either manually or electromotively with a motor or solenoid. Electromotively rotating or moving the secondaiy lens is obvious for those who skilled in the art, and thus the detailed description will be omitted. Also, in addition to those examples, implementing the functions of wide-angle lens and close-up lens may be modified variously within the scope of the present invention.

Meanwhile, as described above in "Disclosure of Invention," a finger support may be included to maintain a regular interval between a lens assembly and a finger. This finger support plays a role in acquiring clearer fingerprint image by preventing the finger from trembling (see Fig. 3).

The concrete structure of the finger support is shown in Figs. 15 to 17. That is, the finger support 133 is pivotally attached on a part of the body of a mobile phone (preferably, adjacent to a camera lens 107), centering around a pivot pin 131. The finger support 133 is rotated around the pivot pin 131 mounted on a side of the mobile phone. It is preferable that the length of the finger support 133 is substantially the same as the focal length of a close-up lens constituted by the primaiy and secondaiy lenses.

In ordinary times, the finger support 133 in Figs. 15 and 1 is closely adhered on the side of a mobile phone in order not to prevent telephone communication and common object photographing. On the other hand, when photographing a fingerprint, the finger support 133 can be erected against the body to distance a finger to prevent it from trembling. The actual usage of the finger support 133 is illustrated in Fig. 17. By standing the finger support 133 and laying a finger on the support 133, the distance between the finger and a camera lens 107 can be regularly maintained and the trembling can be avoided. The rotation of the finger support 133 may be achieved either manually or electromotively by using a motor, solenoid, etc. This operation way is obvious for those skilled in the art.

As described in "Disclosure of Invention" with reference lo Fig. 4, a lighting means for illuminating the fingerprint may be included in the present invention to obtain clearer fingerprint image.

In Fig. 18, it is noted that a light emitting diode 135 is located around the secondary lens 119 held in the secondaiy lens holder 121 or 127. An infrared LED or visible LED may be used for the light emitting diode, and of course any lighting device other than the light emitting diode may be used.

Fig. 19 shows that four light emitting diodes 135a-135d are arranged around the secondary lens holder 121 or 127. In the case that one light emitting diode is used for a lighting device as in Fig. 18, it is impossible to illuminate a round finger tip in uniform light intensity, therefore a part of the fingerprint may be brighter than other parts. However, if a plurality of light emitting diodes are adapted, uniform lighting on the round finger tip is possible.

In the case of Fig. 18, the light emitting diode is controlled to light all times during photographing a fingerprint. On the other hand, in the case of Fig. 19, by sequentially turning on and off the plurality of light emitting diodes, partial images of a fingerprint can be acquired sequentially, and then the acquired partial images can be combined to obtain a complete fingerprint image. This way of image acquisition is well known to those who skilled in the art.

In addition lo lighting method shown in Figs. 18 and 19, other lighting method like Figs. 20 and 21 is possible. Since a fingerprint is an object of a curved surface, a lighting device cannot essentially illuminate uniformly the whole surface of a fingerprint. Therefore relatively great contrast difference occurs between a central portion and a periphery of a fingerprint. In most cases, this contrast problem can be solved by increase the light intensity, but in this invention it is difficult to increase the light intensity to a certain extent because of the amount of electric power for lighting or the physical size of the lighting means. For this, a preferred embodiment of Figs. 20 and 21 may be implemented.

A concept shown in Fig. 20 is that a fingerprint 109 is illuminated by substantially parallel light beams 142 produced, by a converging lens 1 1, from dispersed light 140 that is diffracted by a diffraction grating from the light from a light source 137, rather than it is directly illuminated by the light source. In the case of direct illumination by a single light source, contrast difference between the light illumination areas is great. However, in this embodiment, diffracted light that is diffracted by the diffraction grating 139 is illuminated through a converging lens 141, therefore contrast in the whole surface of a fingerprint becomes uniform.

Fig. 21 shows another embodiment more developed from the embodiment of Fig. 20, of which the configuration is duplication of that shown in Fig. 20. However, diffraction gratings 139a, 139b are arranged such that their grating patterns 143a, 143b are tilted at a given angles. In Fig. 21, a left lighting system is composed of, like in Fig. 20, a first light source 137a, a first diffraction grating 139a, and a first converging lens 141a; a right lighting system is composed of a second light source 137b, a second diffraction grating 139b, and a second converging lens 141b, each of which irradiates lights onto the whole surface of a fingerprint at a lime. As a matter of course, one advantage of this embodiment is that brighter illumination of a fingerprint is achieved relative to that shown in Fig. 20. However, on lop of that, this embodiment is developed especially to scheme the following effect.

Thai is, since the grating patterns 143a, 143b of the first and the second diffraction gratings 139a, 139b are alilt arranged at a given angle, when the light diffracted at the respective first diffraction grating 139a and the second diffraction grating 139b illuminates the fingerprint, constructive or destructive interference occurs according to the light's undulatoiy properties. By using this interference phenomenon, it is possible to make constructively interfered bright light illuminate ridge portions 109a of the fingerprint 109, and to make destructively interfered dark light illuminate valley portions 109b. By doing so, the light contrast between the ridges and the valleys can be emphasized, and thereby clarity and contrast of the photographed fingerprint image can be enhanced.

The fingerprint image acquired by the fingerprint image acquisition device of the present invention and the process of extracting fingerprint data are shown in Figs. 22 to 25. Fig. 22 shows an original image of a photographed fingerprint, Fig. 23 shows binary data obtained from the fingerprint image by means of binarization, Fig. 24 shows line-formed fingerprint image converted from the binary data by means of line fining, and Fig. 25 shows fingerprint data, i.e., minutiae, obtained by a prescribed algorithm. Through Figs. 22 to 25, it can be noted that performance of the device of the present invention is by no means inferior to the conventional contact- type fingerprint acquisition device. According lo the present invention, since it is not necessaiy for a user to closely contact his fingerprint on a fingerprint-reading window to obtain the fingerprint image, fingerprint authentication can be achieved in any situation, and since the latent fingerprint does not stay on the fingerprint- reading window, security can be enhanced. In addition, a function of fingerprint acquisition can be easily added without enlarging the size of a camera-mounted mobile phone.

While the invention has been shown and described with reference to certain embodiments to cany out this invention, 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 invention as defined by the appended claims.

Claims

What Is Claimed Is:

1. An information terminal with a fingerprint acquisition device comprising image-sensing means for converting image to an electrical signal; mode selection means for letting a user select a mode of common object photographing or a mode of fingerprint photographing; lens means for functioning as a wide-angle lens that photographs a common object image when a user selects a mode of common object photographing, and for functioning as a close-up lens that photographs a fingerprint image when a user selects a mode of fingerprint photographing; storage means for storing image data output from the image-sensing means; and sending means for sending the image data output from the image-sensing means to the exterior.

2. An information terminal of claim 1, wherein the lens means comprises a primary lens for focusing an image of common objects onto the image- sensing means when the mode of common object photographing, and a secondaiy lens, installed to be overlapped the primary lens, for focusing an image of a fingerprint onto the image-sensing means when the mode of fingerprint photographing.

3. An information terminal of claim 2, wherein the primary lens is mounted on a body of the information terminal, and the secondary lens is pivotally installed centering around a pivot pin adjacent to the primaiy lens, whereby if the mode of common object photographing is selected, the secondaiy lens rotates in the direction of not overlapping the primaiy lens and the primaiy lens photographs the common objects, while if the mode of fingerprint photographing, the secondaiy lens rotates to overlapping the primary lens, thereby the primaiy lens and the secondaiy lens cooperating to function close-up photographing.

4. An information terminal of claim 3, wherein the rotation of the secondaiy lens is achieved manually or electromotively.

5. An information terminal of claim 2, wherein the primary lens is mounted on a body of the information terminal, and the secondary lens is installed slidably against the body, adjoining the primaiy lens, whereby if the mode of common object photographing is selected, the secondary lens slides in the direction of not overlapping the primaiy lens and the primary lens photographs the common objects, while if the mode of fingerprint photographing, the secondaiy lens slides in the direction of overlapping the primaiy lens, thereby the primaiy lens and the secondaiy lens cooperating to function close- up photographing.

6. An information terminal of claim 5, wherein the sliding movement of the secondaiy lens is achieved manually or electromotively.

7. An information terminal of claim 1, wherein the lens means comprises a primaiy lens fixedly mounted on a body of the information terminal, and a secondaiy lens installed in front of a primary lens, the secondary lens moving back and forth against the primary lens to adjust the distance between the lenses, whereby if the mode of common object photographing is selected, the secondary lens moves proximally to the primaiy lens and the primaiy and secondaiy lenses focus an image of common objects onto the image-sensing means, while if the mode of fingerprint photographing, the secondaiy lens moves away from the primaiy lens such that a focal length is changed, and the primary and secondaiy lenses focus an image of a fingerprint onto the image-sensing means.

8. An information terminal of claim 7, wherein the reciprocal movement of the secondaiy lens is achieved manually or electromotively.

9. An information terminal of claim 1 or 2, further comprising a finger support for maintaining a regular interval between the lens means and a finger, the finger support playing a role in acquiring clearer fingerprint image by preventing the finger from trembling.

10. An information terminal of claim 9, wherein the finger support is pivotally attached on a part of the body of the information terminal, centering around a pivot pin, and a length of the finger support is substantially the same as a focal length of the lens means, whereby in the mode of common object photographing, the finger support is closely adhered on the side of the information terminal, while in the mode of fingerprint photographing, the finger support rotates and erects against the body to distance a finger to prevent it from trembling.

11. An information terminal of claim 10, wherein the rotation of the finger support is achieved manually or electromotively.

12. An information terminal of claim 10, further comprising at least one lighting means for illuminating the fingerprint to obtain clearer fingerprint image.

13. An information terminal of claim 12, wherein the lighting means is sequentially turned on and off to photograph partial images of the fingerprint and then the photographed partial images can be combined to obtain a complete fingerprint image.

14. An information terminal of claim 2, further comprising lighting means for illuminating the fingerprint when the mode of fingerprint photographing is selected, the lighting means comprising: a light source, a diffraction grating for diffracting a light from the light source, a converging lens for producing substantially parallel light beams from dispersed light that is diffracted by the diffraction grating.

15. An information terminal of claim 2, further comprising lighting means for illuminating the fingerprint when the mode of fingerprint photographing is selected, the lighting means comprising a first illumination means and a second illumination means, the first illumination means comprising a first light source; a first diffraction grating for diffracting a light from the light source; a first converging lens for producing substantially parallel light beams from dispersed light that is diffracted by the first diffraction grating, the first diffraction grating being arranged such that its grating pattern is positioned in a first angle, and the second illumination means comprising a second light source; a second diffraction grating for diffracting a light from the light source; a second converging lens for producing substantially parallel light beams from dispersed light that is diffracted by the second diffraction grating, the second diffraction grating being arranged such that its grating pattern is tilled at a pre-scribed angle against the first angle, whereby, by using constructive and destructive interference phenomenon of the light from the first illumination means and the second illumination means, constructively interfered bright light is made to illuminate ridge portions of the fingerprint, and destructively interfered dark light illuminate valley portions of the fingerprint.