JP2020086749A - Imaging device and imaging method - Google Patents

Abstract

To improve the contrast of a captured image.SOLUTION: An imaging device 1 of the present invention comprises: a first light source unit 2 for outputting first light; a second light source unit 3 for outputting second light having a longer wavelength than the first light; an optical element 4 having a contact surface to which an object contacts; and a first imaging unit 5 for imaging the object irradiated with the first light and the second light through the optical element 4.SELECTED DRAWING: Figure 1

Description

The present invention relates to an imaging device and an imaging method.

Patent Document 1 shows a fingerprint input device that acquires a fingerprint image from a light beam that is emitted from a light source to a finger, diffuses in the finger, and is reflected. In the fingerprint input device described in Patent Document 1, an LED (Light emitting diode) is arranged as a transmissive light source around a light transmissive plate on which a finger is placed.

JP, 2003-216939, A

In the determination device described in Patent Document 1, the center portion of the transmitted light image tends to be darker than the peripheral portion. Therefore, there is a problem that it may be difficult to acquire an image that has a high contrast over the entire fingerprint and is advantageous for fingerprint matching.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an imaging device and an imaging method capable of improving the contrast of a captured image.

In order to solve the above problems, one embodiment of the present invention includes a first light source portion which outputs first light, a second light source portion which outputs second light having a wavelength longer than the first light, and a target. It is an imaging device provided with an optical element which has a contact surface with which an object contacts, and a 1st imaging part which picturizes an object irradiated with the 1st light and the 2nd light through the optical element.

Further, according to one embodiment of the present invention, a first image pickup is performed using a first light source unit that outputs first light and a second light source unit that outputs second light having a wavelength longer than the first light. It is an imaging method for imaging an object irradiated with the first light and the second light by a unit.

According to each aspect of the present invention, the contrast of a captured image can be improved.

It is a schematic block diagram which shows the minimum structural example of this invention. It is a schematic diagram which shows the structural example of the imaging device 1 which concerns on 1st Embodiment of this invention. FIG. 3 is a perspective view showing a configuration example of the image pickup apparatus 1 shown in FIG. 2. FIG. 3 is a schematic diagram for explaining an operation example of the image pickup apparatus 1 shown in FIG. 2. FIG. 3 is a schematic diagram for explaining an operation example of the image pickup apparatus 1 shown in FIG. 2. FIG. 4 is a diagram showing an example of an image measured by the image pickup apparatus 1 shown in FIGS. 2 and 3 and a signal waveform thereof. It is explanatory drawing of the direction in the image shown in FIG.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a minimum configuration example of an image pickup apparatus according to an embodiment of the present invention. The imaging device 1 shown in FIG. 1 includes a first light source unit 2, a second light source unit 3, an optical element 4, and a first imaging unit 5. The first light source unit 2 outputs the first light. The second light source unit 3 outputs second light having a wavelength longer than that of the first light. The optical element 4 has a contact surface with which an object to be imaged comes into contact. The first image capturing unit 5 captures an image of the object irradiated with the first light and the second light through the optical element 4.

According to the image pickup apparatus 1 shown in FIG. 1, a light beam from an object to be imaged can be guided to the first image pickup section via the optical element 4 and an image signal can be obtained. Here, since the second light output from the second light source unit 3 has higher transparency than the first light output from the first light source unit 2, it is difficult to brighten the second light with the first light. The part of the object can be brightened with the second light. Therefore, according to the imaging device 1, the contrast of the captured image can be improved.

Next, with reference to FIG. 2, a first embodiment of the imaging device 1 shown in FIG. 1 will be described. FIG. 2 is a front view schematically showing the first embodiment of the image pickup apparatus 1 shown in FIG. In FIG. 2, configurations corresponding to those shown in FIG. 1 are designated by the same reference numerals. In the example shown in FIG. 2, the object to be imaged is a finger end portion (end portion of a human finger) 7. The imaging device 1 has one purpose to image a fingerprint on the ventral surface of the finger end 7 as a physical feature for biometric authentication. However, the object to be imaged by the imaging device 1 is not limited to the finger end, and may be the palm or the like. That is, the image capturing apparatus 1 may have one purpose to image other physical features for biometric authentication such as a palm print. For example, from the base of the finger to the base of the finger to the base of the finger. It is possible to adopt an arbitrary position, the entire finger, or the like. When using an image of a part other than the fingertip, a feature other than the fingerprint, for example, a wrinkle pattern image of the skin may be used. In addition, the target of image acquisition by the imaging device 1 is not limited to a part of the body.

In the example illustrated in FIG. 2, the imaging device 1 includes a second imaging unit 6 in addition to the first light source unit 2, the second light source unit 3, the optical element 4, and the first imaging unit 5 illustrated in FIG.
In the illustrated example, the prism 4 used as an optical element includes a contact surface 4a with which a finger end 7 as an object contacts, an intersecting surface 4b that intersects with the contact surface 4a at a predetermined angle θ1, and a facing surface that faces the contact surface 4a. It has a surface 4c and a surface 4d. The prism 4 of this example is a polyhedron (for example, a hexahedron) having a refractive index different from that of air, and can be formed of, for example, glass, crystal, or the like. Further, in the example shown in FIG. 2, the angle θ1 formed between the constituent surfaces is an acute angle. However, the angle θ1 is not limited to an acute angle, and may be an obtuse angle or a right angle. The facing surface 4c may or may not be parallel to the contact surface 4a. A blackboard 41 is attached to the surface 4d facing the intersecting surface 4b in order to enhance the contrast of the image. However, black paint or the like may be applied to the surface 4d instead of the blackboard 41. The optical element 4 is not limited to a prism, but can be a lens, a reflecting mirror, an optical fiber, or a combination thereof that can guide a light beam from a light source to an object and can guide a light beam from the object to the imaging device 1. May be
In the arrangement of the second image pickup unit 5 shown in FIG. 3, the angle θ1 formed between the constituent surfaces is an acute angle, but the angle θ1 formed is not limited to an acute angle, and the second image pickup unit 5 is arranged below, for example. For example, depending on the arrangement of the image pickup unit, the angle may be an obtuse angle or a right angle.

The first light source unit 2 is provided below the optical element 4, has a visible light LED 2a such as a white LED (Light emitting diode light emitting diode), and outputs the first light L1 upward in FIG. To do. In this case, the first light L1 contains a large amount of visible light components having a wavelength of about 380 to 800 nm. Further, in the example shown in FIG. 2, the first light L1 output from the visible light LED 2a is emitted from the facing surface 4c side of the optical element 4 to the finger end portion 7 which is the object.

The second light source unit 3 is provided on the contact surface 4a on the optical element 4, has a plurality of infrared LEDs 3a and 3b, and receives the second light L2 having a wavelength longer than that of the first light L1 from the contact surface 4a. Along with the output toward the finger end 7. In this case, the second light L2 contains many infrared components having a wavelength of about 800 nm to 1000 nm. Further, in the example shown in FIG. 2, the second light L2 output by the infrared LEDs 3a and 3b is emitted from the peripheral portion on the contact surface 4a to the finger end portion 7 which is the object.

The first image capturing unit 5 captures an image of the finger end 7 that is the object from the side of the intersecting surface 4b. The first image pickup unit 5 has an image pickup device such as a CMOS (Complementary metal oxide semiconductor) image sensor or a CCD (Charge coupled device) image sensor, and the input visible light component and infrared rays. The component is converted into an image signal and output. In this case, the first imaging unit 5 has a high sensitivity to the first light L1 and the second light L2 (has a predetermined sensitivity to the first light L1 and the second light L2).

The 2nd imaging part 6 picturizes finger end part 7 which is an object from the opposed surface 4c side. The second image pickup unit 6 has an image pickup element such as a CMOS image sensor or a CCD image sensor and an infrared cut filter, and converts the input visible light component into an image signal and outputs it. In this case, the second imaging unit 6 has a low sensitivity to the second light L2 (has a predetermined sensitivity to the first light L1 and a predetermined sensitivity to the second light L2. Not). However, the second imaging unit 6 may not have the infrared cut filter, and may obtain the same effect as the case where the infrared cut filter is provided by image processing or the like, for example.

FIG. 3 is a perspective view schematically showing an arrangement example of each part of the image pickup apparatus 1 shown in FIG. In FIG. 3, components corresponding to those shown in FIG. 2 are designated by the same reference numerals. In the imaging device 1 shown in FIG. 3, the first light source unit 2 is composed of four white LEDs 2a, 2b, 2c and 2d arranged on the facing surface 4c side of the prism 4 as an optical element. The four white LEDs 2a, 2b, 2c and 2d are mounted on a substrate 43 that fixes the facing surface 4c side of the prism 4. The second light source unit 3 is composed of eight infrared LEDs 3a, 3b, 3c, 3d, 3e, 3f, 3g and 3h arranged in the peripheral portion on the contact surface 4a of the prism 4. The eight infrared LEDs 3a, 3b, 3c, 3d, 3e, 3f, 3g and 3h are mounted on the substrate 42 that fixes the contact surface 4a side of the prism 4. The number of LEDs is not limited to the example shown in FIG.

Next, each optical path in the prism 4 shown in FIG. 2 will be described with reference to FIGS. 4 and 5. FIG. 4 is an enlarged schematic view of the contact surface 4a and the finger end portion 7 shown in FIG. FIG. 5 is a schematic view showing the prism 4 and the finger end portion 7 shown in FIG. 2 in an enlarged manner. As described above, the image pickup apparatus 1 of the present embodiment has one purpose to take an image of a fingerprint, which is one of the biological characteristics. The fingerprint is composed of a combination of irregularities (valley line portion 72 and ridge portion 71) on the abdominal surface 7a of the finger end portion 7. The first light L1 output from the first light source unit 2 is reflected by the ridges 71 and the valleys 72 provided on the contact surface 4a and enters the prism 4. In addition, the second light L2 output from the second light source unit 3 passes through the finger end portion 7, is emitted from the ridge portion 71 and the valley line portion 72 installed on the contact surface 4a, and is emitted from the contact surface 4a. It is incident on the prism 4.

As shown in FIG. 4, since the ridge 71 of the finger end 7 is in contact with the contact surface 4a, the refractive index of light incident on or reflected by the ridge 71 is the prism 4( It is almost the same as the refractive index of glass, etc.). Therefore, the light emitted from the ridge 71 or reflected by the ridge 71 can be considered in the same manner as the light reflected by the contact surface 4a, and as shown by the chain line arrow, almost all directions in the prism 4 can be considered. Is almost uniformly radiated on the contact surface 4a and can reach all areas below the contact surface 4a.

On the other hand, the valley line portion 72 is not in contact with the contact surface 4a, and the air layer 8 is present between the valley line portion 72 and the contact surface 4a. Therefore, the light emitted from the valley line portion 72 or the light reflected by the valley line portion 72 enters the contact surface 4 a via the air layer 8. Here, the refractive index of air is 1.0, glass is generally in the range of 1.5 to 1.3 to 2.0, 1.3 to 1.5, and water and skin are 1.3 to 1.4. Since there is a difference in the refractive index, the light emitted and reflected from the valley line portion 72 undergoes a refraction phenomenon different from the light emitted and reflected light from the ridge portion 71 and is not emitted in all directions. Further, since the refraction angle is smaller than the incident angle, the emitted light from the valley line portion 72 and the reflected light at the valley line portion 72 are biased to the downward light in the prism 4 as indicated by the broken line arrow. ..

As described with reference to FIG. 4, the light from the ridge 71 is radiated from the contact surface 4a almost uniformly in all directions, and the light from the valley 72 is biased downward from the contact surface 4a. Is emitted. Further, since the light from the valley portion 72 is radiated in a downward direction, the angle of incidence on the intersecting surface 4b is larger than that of the light from the ridge portion 71, as shown in FIG. Therefore, as compared with the light from the ridge portion 71, the incident angle of the light from the valley portion 72 exceeds the critical angle, and the total reflection at the intersecting surface 4b increases. Therefore, the light from the ridge portion 71 reaches more than the light from the valley portion 72 to the first imaging unit 5 which images the finger end portion 7 from the side of the intersecting surface 4b. Therefore, the image captured by the first imaging unit 5 is an image in which the ridges 71 are bright and the valleys 72 are dark, and a fingerprint image with high contrast (hereinafter referred to as a high-contrast image). Further, at the time of imaging, the finger end portion 7 is illuminated with the first light L1 from the facing surface 4c side, and is illuminated with the second light L2 from the peripheral portion of the contact surface 4a. In this case, the peripheral portion of the finger end 7 where the first light L1 is hard to reach can be brightened by the second light L2. Therefore, the 1st imaging part 5 can image a fingerprint in the state where the whole fingerprint was appropriately illuminated. Therefore, according to this embodiment, the contrast can be increased over the entire fingerprint image.

On the other hand, the light from the ridge line portion 71 and the light from the valley line portion 72 are compared with the arrival rate of the first image pickup unit 5 to the second image pickup unit 6 which picks up the image of the finger end 7 from the facing surface 4c side. And arrive at a roughly even rate. The image captured by the second image capturing unit 6 is the same image as when the finger end portion 7 installed on the contact surface 4a is directly viewed from the facing surface 4c. The image captured by the second imaging unit 6 is an image in which the infrared component is suppressed. Therefore, the image captured by the second image capturing unit 6 is a natural image of the finger end portion 7 (hereinafter referred to as a natural image). However, as described above, the infrared component may not be suppressed depending on the use of the image captured by the second image capturing unit 6.

The high-contrast image captured by the first imaging unit 5 is used for fingerprint matching, for example. At that time, it is desirable that the first imaging unit 5 captures a fingerprint image in a wider area so that many feature points exist. In the present embodiment, the first imaging unit 5 can capture a fingerprint image with high contrast over the entire area, so that the accuracy of fingerprint matching can be easily increased, for example. On the other hand, the natural image picked up by the second image pickup unit 6 is used, for example, to determine whether it is a fake or a real one.

As described above, according to the image capturing apparatus 1 of the present embodiment, it is possible to capture a wider area with a high contrast in a fingerprint image having many feature points, and, for example, a natural image for detecting forgery. Images can be taken at the same time.

As shown in FIG. 2, the image pickup apparatus 1 of the present embodiment outputs the first light source unit 2 that outputs the first light L1 and the second light L2 that has a wavelength longer than that of the first light L1. The second light source unit 3, the prism 4 having the contact surface 4a with which the target object such as the finger end 7 contacts, and the target object irradiated with the first light L1 and the second light L2 are imaged through the prism 4. The first imaging unit 5 is provided. According to this configuration, since the second light L2 has higher transparency than the first light L1, it is possible to brighten the portion that is difficult to brighten with the first light L1 with the second light L2. Images with high contrast can be captured.

Further, in the imaging device 1 of the present embodiment, the second light L2 is emitted from the peripheral portion on the contact surface 4a to the target object. With this configuration, the peripheral portion of the object can be efficiently irradiated with the second light L2.

Further, in the image pickup apparatus 1 of the present embodiment, the prism 4 has the intersecting surface 4b that intersects the contact surface 4a at a predetermined angle θ1, and the first imaging unit 5 images the object from the intersecting surface 4b side. According to this configuration, the first imaging unit 5 can capture a high-contrast image.

Further, in the image pickup apparatus 1 of this embodiment, the angle θ1 is an acute angle. With this configuration, the prism 4 can be easily downsized even if the contact surface 4a is widened.

Further, in the image pickup apparatus 1 of the present embodiment, the prism 4 has the facing surface 4c that faces the contact surface 4a, and the first light L1 is applied to the object from the facing surface 4c side. According to this configuration, it is possible to uniformly irradiate the entire object with the first light L1.

Further, the image pickup apparatus 1 of the present embodiment includes the second image pickup unit 6 that picks up an image of the target object from the facing surface 4c side. According to this configuration, it is possible to capture a high-contrast image with the first imaging unit 5 and simultaneously capture a natural image with the second imaging unit 6.

Further, in the image pickup apparatus 1 according to the present embodiment, the first image pickup section 5 has high sensitivity to the first light L1 and the second light L2, and the second image pickup section 6 receives the second light L2. It has low sensitivity. It is possible to capture a high-contrast image with the first imaging unit 5 and simultaneously capture a natural image with higher color reproducibility with the second imaging unit 6.

In addition, in the imaging device 1 of the present embodiment, the first light L1 contains a large amount of visible light components, and the second light L2 contains a large amount of infrared components. According to this configuration, since the second light L2 has higher transparency than the first light L1, it is possible to brighten the portion that is difficult to brighten with the first light L1 with the second light L2.

Next, with reference to FIGS. 6 and 7, a result of actually capturing a high-contrast image by the image capturing apparatus 1 of the above-described embodiment will be described. FIG. 6 shows an image captured by the first image capturing unit 5 and the brightness obtained by changing the energizing current I of the eight infrared LEDs 3a to 3h by turning on the four white LEDs 2a to 2d in the image capturing apparatus 1 shown in FIG. The measurement result of the value is shown. FIG. 6A shows an image captured with the energizing current I set to 0 mA (extinguished) and the change in the luminance value depending on the positions in the three directions D1, D2, and D3 shown in FIG. 7 in arbitrary units. FIG. 6B shows an image captured with the energizing current I of 6 mA, and a change in the brightness value depending on the positions in the three directions D1, D2, and D3 shown in FIG. 7 in the image in arbitrary units. FIG. 6C shows an image captured with the energization current I of 13 mA, and the change in the brightness value depending on the positions of the three directions D1, D2, and D3 shown in FIG. 7 in the image in arbitrary units. FIG. 6D shows an image captured with the energizing current I of 20 mA, and the change in the luminance value depending on the positions of the three directions D1, D2, and D3 shown in FIG. 7 in the image in arbitrary units. Compared with the case where the eight infrared LEDs 3a to 3h shown in FIG. 6(a) are turned off (I=0 mA), when the energizing current I shown in FIG. 6(d) is 20 mA, each direction D1 to D3. In contrast, the contrast (ratio of brightness between the brightest part and the darkest part) is improved by about 10% to 20%.
By distinguishing the direct-view image from the contrast camera and changing the prism shape and arranging the infrared camera, the optical path length between the finger and the infrared camera is shortened, and the fingerprint is taken at the full angle of view (large). As a result, the fingerprint can be captured with high resolution.

In the above-described image pickup apparatus, the combination of the timing of image pickup by the first image pickup unit 5 and the second image pickup unit 6 and the timing of light emission of the first light L1 and the second light L2 at the time of image pickup is different from that of the embodiment. The following timing may be adopted.
The shooting of the natural image by the second imaging unit 6 and the shooting of the high-contrast image by the first imaging unit 5 may be interchanged. Further, at the time of this image pickup, the white LEDs 2a to 2d and the infrared LEDs 3a to 3h are turned on at the same time, or during the simultaneous turning on, the second image pickup unit 6 shoots a natural image and then the first image pickup unit 5 shoots. Alternatively, the images may be taken in the reverse order.
In addition, the first image pickup unit 5 and the second image pickup unit 6 may be photographed at the same time. Further, at the time of this photographing, the white LEDs 2a to 2d and the infrared LEDs 3a to 3h may be turned on at the same time.
In this way, by appropriately combining the timings of photographing and lighting, it is possible to shorten the lighting time of the white LEDs 2a to 2d and the infrared LEDs 3a to 3h, or to reduce the number of blinks. Further, the above-mentioned lighting and image capturing timings can be set to an optimum combination as needed, depending on the usage mode of the apparatus.

Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to the above-described embodiments, and includes design changes and the like without departing from the scope of the present invention.

The whole or part of the exemplary embodiments disclosed above can be described as, but not limited to, the following.

(Appendix 1)
A first light source unit that outputs a first light;
A second light source unit that outputs second light having a wavelength longer than that of the first light;
An optical element having a contact surface with which an object contacts,
A first image pickup section that detects a light beam from an object irradiated with the first light and the second light through the optical element.

(Appendix 2)
The imaging device according to appendix 1, wherein the second light is emitted from the peripheral portion on the contact surface to the target object.

(Appendix 3)
The optical element is a prism, and the prism has an intersecting surface that intersects the contact surface at a predetermined angle,
The imaging device according to any one of appendices 1 and 2, wherein the first imaging unit images the object from the intersecting surface side.

(Appendix 4)
The imaging device according to appendix 3, wherein the angle formed is an acute angle.

(Appendix 5)
The optical element has a facing surface facing the contact surface,
The imaging device according to any one of appendices 1 to 4, wherein the first light is irradiated onto the object from the facing surface side.

(Appendix 6)
The imaging device according to appendix 5, further comprising a second imaging unit that images the object from the facing surface side.

(Appendix 7)
The first imaging unit is highly sensitive to the first light and the second light,
The imaging device according to appendix 6, wherein the second imaging unit has low sensitivity to the second light.

(Appendix 8)
The first light contains a large amount of visible light component,
The imaging device according to any one of appendices 1 to 7, wherein the second light contains a large amount of infrared components.

(Appendix 9)
The imaging device according to claim 1, wherein the target object is a finger end portion.

(Appendix 10)
The first light and the second light are turned on at the same time,
8. The image pickup apparatus according to any one of appendixes 6 and 7, wherein the image pickup by the first image pickup unit and the image pickup by the second image pickup unit are performed at a different timing.

(Appendix 11)
Lighting the first light and the second light at the same time,
8. The image pickup apparatus according to any one of appendices 6 and 7, wherein the image pickup by the first image pickup unit and the image pickup by the second image pickup unit are performed at the same time.

(Appendix 12)
A first light source unit that outputs a first light;
And a second light source section that outputs a second light having a wavelength longer than that of the first light,
An imaging method for imaging an object irradiated with the first light and the second light by a first imaging unit.

1 Imaging device 2 1st light source part 2a-2d White LED
3 2nd light source part 3a-3h Infrared LED
4 Optical element (prism)
4a Contact surface 4b Intersection surface 4c Opposing surface 5 First imaging unit 6 Second imaging unit 7 Finger end L1 First light L2 Second light

Claims (10)

A first light source unit that outputs a first light;
A second light source unit that outputs second light having a wavelength longer than that of the first light;
An optical element having a contact surface with which an object contacts,
A first image pickup section that detects a light beam from an object irradiated with the first light and the second light through the optical element. The imaging device according to claim 1, wherein the second light is emitted to the object from a peripheral portion on the contact surface. The optical element is a prism, and the prism has an intersecting surface that intersects the contact surface at a predetermined angle,
The imaging device according to claim 1, wherein the first imaging unit images the object from the side of the intersecting surface. The imaging device according to claim 3, wherein the formed angle is an acute angle. The optical element has a facing surface facing the contact surface,
The imaging device according to claim 1, wherein the first light irradiates the object from the facing surface side. The imaging device according to claim 5, further comprising a second imaging unit that images the object from the facing surface side. The first light contains a large amount of visible light component,
The image pickup apparatus according to claim 1, wherein the second light contains a large amount of infrared components. Lighting the first light and the second light at the same time,
The image pickup apparatus according to claim 6, wherein the image pickup by the first image pickup unit and the image pickup by the second image pickup unit are performed at a different timing. Lighting the first light and the second light at the same time,
The image pickup apparatus according to claim 6, wherein image pickup by the first image pickup section and image pickup by the second image pickup section are performed at the same time. A first light source unit that outputs a first light;
And a second light source section that outputs a second light having a wavelength longer than that of the first light,
An imaging method of imaging an object irradiated with the first light and the second light by a first imaging unit.

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