JPH0664602B2 - Rough surface information detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In a device for acquiring a fingerprint image by using total reflection light propagating inside a glass plate in contact with a finger, the intensity of laser light illuminating a fingerprint is measured with respect to the glass plate. In order to control so that it is strong when the finger pressing force is low and weak when the finger pressing force is high, a pressure sensor for measuring the pressing force and multiple filters with different light transmittances are provided. One filter selected based on
It is arranged between the glass plate and the laser light source.

[Industrial application field]

The present invention relates to an apparatus for optically detecting a pattern represented by unevenness, and more particularly to a sensor for inputting fingerprint information in a system for discriminating fingerprints.

[Conventional technology]

In order to ensure the security of computer systems, personal verification using ID cards and passwords is performed. On the other hand, in this field as well, it has been attempted to establish a higher level of security by utilizing the “universal difference” and “lifetime immutability” characteristics of fingerprints. Using fingerprints can avoid inconveniences such as inadequate portability, plagiarism, and tampering.

For the above purpose, it is necessary to immediately discriminate fingerprints, and for this purpose, a method of optically detecting fingerprint information has been proposed. What is important here is to detect fingerprints with high contrast. As one of the methods, when a finger is pressed against a transparent flat plate such as a glass plate, a part of the light scattered by the convex portion (ridge) of the fingerprint which is in contact with the glass plate is reflected inside the glass plate. The light that propagates by total reflection but is scattered by the concave portion (valley line) that is not in contact with the glass plate cannot satisfy the above conditions for total reflection,
There is a method that utilizes the fact that after entering the glass plate, it is transmitted through the glass plate and then emitted to the outside again. That is, a high-contrast fingerprint image can be obtained by extracting and forming an image of the totally reflected light. Using this principle, various improved models have been proposed. (JP-A-55
-81321, Japanese Patent Laid-Open No. 61-201380, etc.) [Problems to be Solved by the Invention] In the fingerprint detecting device as described above, the contact state of the finger with respect to the glass plate, that is, the pressing force of the finger or the smoothness of the skin. The intensity of the scattered light due to the fingerprint changes depending on the degree of sweating and the like. Particularly, in the case of rough skin, the adhesion to the glass plate is poor and scattered light becomes weak. as a result,
The brightness of the fingerprint image projected on the imaging device is low. Various errors are likely to occur when processing such a fingerprint image to obtain image information, that is, information about the characteristic points of the fingerprint. For example, an error in binarization due to improper slice level in the binarization process of the output signal from the imaging device,
Further, there is an error in discriminating the end points or branch points of the fingerprint in the thinning process or the restoration process for selecting the characteristic points representing the fingerprint.

In the conventional apparatus, the countermeasure for preventing the error in the above-mentioned processing is dominated by the processing algorithm. Therefore, there are problems that the processing algorithm becomes complicated, the detection efficiency is low, and the reliability of the obtained information is low.

[Means for solving problems]

The above-mentioned problems are caused by a transparent flat plate (10) having one flat surface provided with an uneven surface information input section with which the soft test uneven surface (12) is contacted and another flat surface parallel to the flat surface, and the uneven surface. (12)
Of the flat plate (10) after being scattered by the convex portion of the transparent plate and incident on the transparent flat plate (10) and propagating inside the transparent flat plate (10) to the outside of the transparent flat plate (10). (14) provided on the laser, a laser light source (20) for illuminating the uneven surface (12) to be inspected that is in contact with the transparent flat plate (10), and diffraction emitted from the hologram (14). A concave-convex surface information detecting device comprising an image sensor (30) for detecting an image, the pressure sensor (40) for measuring a pressing force of the concave-convex surface (12) to be tested against the transparent flat plate (10). A filter (22) arranged between the uneven surface (12) to be tested and the laser light source (20), and for changing the transmittance of the filter (22) based on the pressing force. The unevenness surface information detecting device of the present invention is characterized by having a transmittance adjuster (24).

[Action]

By controlling the transmittance of the filter to be small when the pressing force of the finger on the transparent flat plate is large, the intensity of the scattered light by the fingerprint is controlled to a substantially constant level. This reduces the burden on the fingerprint discrimination algorithm. That is, the algorithm can be simplified, and as a result, the processing efficiency and the reliability of the obtained pattern information can be improved.

〔Example〕

FIG. 1 is a schematic diagram showing an outline of the configuration of an uneven surface information detecting device according to the present invention. A finger 12 is pressed against the surface of the transparent flat plate 10. A hologram 14 is formed on the surface of one end of the transparent flat plate 10. The hologram 14 is a transparent flat plate 10.
Apart from the ones made using photographic film,
It may be attached to the transparent flat plate 10.

The surface of the finger 12 in contact with the transparent flat plate 10 is the laser light source 20.
When irradiated by the light from, the light scattered by the ridges of the fingerprint of the finger 12 and a part of the light incident on the inside of the transparent plate 10 propagates through the inside while being totally reflected on the surface of the transparent plate 10. . On the other hand, the light scattered by the valley line of the fingerprint does not satisfy the condition of total reflection even if it is incident on the transparent flat plate 10.
It passes through 10 and goes out again. In this way, only the scattered light from the ridges of the fingerprint enters the hologram 14. The scattered light is diffracted by the hologram 14 and is formed as a fingerprint image on the light receiving surface of the image pickup device 30, such as a CCD. The fingerprint image is decomposed into pixels and stored in the frame memory 31.

Further, in the uneven surface information detecting device of the present invention, the finger 12
And a laser light source 20 provided between the filter 21 and the laser light source 20, the transmittance of which can be changed, and when the finger 12 comes into contact with the transparent flat plate 10, this is detected and a signal of a value corresponding to the pressing force of the finger 12 is output. Pressure sensor 40, and when the output of the pressure sensor 40 is less than or equal to a value corresponding to a predetermined pressing force, an alarm signal (eg, buzzer sound)
In response to the output of the alarm device 41 and the pressure sensor 40,
A transmittance adjuster 22 that controls the transmittance of the filter 21 to a predetermined value.
Is provided.

The operation of the uneven surface information detecting device will be described with reference to the flow chart of FIG. First, the finger is brought into contact with the uneven surface information input section on the transparent plate by step fingerprint input. Then, the pressure force of the finger is measured by the pressure sensor. In step, it is determined whether or not the pressing force is a predetermined value or more,
If it is less than a predetermined value, an alarm signal will be output and
Return to the step again.

If the pressing force is equal to or larger than the predetermined value in the step, the transmittance adjuster sets the transmittance of the filter to the predetermined value corresponding to the pressing force in the step based on the control signal sent from the pressure sensor. After that, in step, an image (fingerprint image emitted from the hologram) is captured by the imaging device. After that, this image is processed, the feature points of the fingerprint are extracted, and the feature point information (type and coordinates of feature points)
Is stored (registered) in the memory. At the time of matching, the characteristic point information extracted from the image (fingerprint) captured by the same procedure as described above is compared with the characteristic point information registered in the memory in advance.

FIG. 3 is a graph showing the relationship between the pressing force and the transmittance of the filter set corresponding to the pressing force. As mentioned above,
Generally, when the pressing force is low, the intensity of scattered light due to fingerprints is weak. Therefore, as shown in the figure, the transmittance of the filter is controlled so that the pressing force is 100% when the pressing force is substantially a predetermined value and decreases to about 50% as the pressing force increases. In this way, the scattered light intensity due to the fingerprint is adjusted to be substantially equal under any pressing force.

Since the value of such transmittance does not necessarily have to change continuously, for example, a plurality of filters having a difference in transmission of about 10% are attached to a support frame, and the support frame is adjusted by the transmittance adjuster. It is also possible to drive and arrange a filter having an appropriate transmittance from the plurality of filters. Further, the filter may be configured using a liquid crystal panel whose transmittance changes according to the applied voltage.

〔The invention's effect〕

According to the present invention, since the brightness of the fingerprint image input to the image pickup device is maintained at a substantially constant level, there is an effect that the efficiency and reliability of fingerprint discrimination processing can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an uneven surface information detecting device according to the present invention, FIG. 2 is a flow chart for explaining the operation of the uneven surface information detecting device according to the present invention, and FIG. It is a graph which shows the relationship between the pressing force and the transmittance of the filter set corresponding to this. In the figure, 10 is a transparent flat plate, 12 is a finger, 14 is a hologram,
20 is a laser light source, 22 is a filter, 24 is a transmittance adjuster, 30
Is an imaging device, 32 is a frame memory, 40 is a pressure sensor, 42
Is an alarm.

Claims (3)

[Claims] 1. A transparent flat plate (10) having one flat surface provided with an uneven surface information inputting portion to which a soft uneven surface (12) to be inspected is provided and another flat surface parallel to the flat surface (10), and the uneven surface (10). The scattered light that has been scattered by the convex portions of 12) and then enters the transparent flat plate (10) and propagates inside the transparent flat plate (10) under the condition of total internal reflection is the transparent flat plate (10).
A hologram (14) provided on one of the flat surfaces for guiding the light to the outside of the laser and a laser light source for illuminating the subject uneven surface (12) in contact with the transparent flat plate (10) ( A concave-convex surface information detecting device comprising an image pickup device (30) for detecting a diffraction image emitted from the hologram (14), the concave-convex surface ( A pressure sensor (40) for measuring the pressing force of 12), a filter (22) arranged between the uneven surface (12) to be tested and the laser light source (20), and based on the pressing force, An uneven surface information detecting device, comprising: a transmittance adjuster (24) for changing the transmittance of the filter (22). 2. A plurality of filters having different transmissivities are provided, and the transmissivity adjuster (24) selects one of the plurality of filters based on the pressing force value measured by the pressure sensor (40). The uneven surface information detecting device according to claim 1, wherein (22) is selected and arranged between the uneven surface (12) to be inspected and the laser light source (20). 3. The uneven surface information detecting device according to claim 1, further comprising an alarm device (42) for issuing an alarm when the pressing force is a predetermined value or less.