JPH01307886A - Contact type fingerprint detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Table of Contents Overview Industrial Application Fields Prior Art (Figure 4.5) Problems to be Solved by the Invention Examples of Means and Actions for Solving the Problems (1st to 4th Embodiments) Figure 3) Effects of the extended invention [Summary] Regarding a contact fingerprint detection device that optically converts the contact state of a finger to a light guide member into a fingerprint image, a clear and wide fingerprint image can be obtained regardless of individual differences in sweating, etc. For this purpose, the brightness of the fingerprint image is set to a threshold value S. After the threshold value 5l (sl>s
o); a second time measuring means that measures the elapse of a predetermined time t corresponding to the measured time t1 after the luminance reaches the threshold S1; The fingerprint image obtained by the time t measurement by the second time measuring means is used in the verification process or the registration process.

[Industrial Field of Application] The present invention relates to a contact type fingerprint detection device that optically converts the contact state of a finger to a light guide member into a fingerprint image.

[Background Art] In recent years, as computers have been introduced into a wide range of social systems, system security has become a focus of interest from all concerned. Many questions have been raised regarding the security of ID cards and passwords, which have been used up until now to verify identity when entering computer rooms or using terminals. Fingerprints, on the other hand, are considered the most effective means of identifying individuals because they are unique and unchanging throughout life, and much research and development has been conducted on simple personal identification systems using fingerprints. There is.

Contact-type fingerprint detection devices utilize the fact that when a finger is pressed against a light guide plate (for example, a glass plate), the reflectance and transmittance of light change on the contact surface, and the light from the light source is directed to this boundary surface. Light that enters from the light guide plate side or the finger side, is reflected by the boundary surface, or is transmitted through the boundary surface and is totally reflected inside the light guide plate is guided to the image sensor to detect a fingerprint image.

In order to reliably register and verify fingerprint images, it is necessary to obtain clear fingerprint images over a wide area. Therefore, it is desirable that the fingers sweat appropriately and be in close contact with the light guide plate.

[Problems to be Solved by the Invention] However, there are individual differences in sweating, and even in the same person, the degree of sweating varies depending on the psychological state at the time. As shown in FIG. 4, for people who sweat relatively vigorously, the brightness S of the fingerprint image is at the threshold S over a wide range. However, for people who sweat relatively slowly, the brightness S of the fingerprint image is equal to the threshold S, as shown in FIG. The range beyond which the fingerprint is measured is narrow, and therefore only an unclear and narrow fingerprint image may be obtained.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a contact-type fingerprint detection device that can obtain a clear and wide fingerprint image regardless of individual differences in sweating.

[Means for Solving the Problems] In order to achieve this object, the present invention provides a contact fingerprint detection device that optically converts the contact state of a finger to a light guide member into a fingerprint image. The brightness of the fingerprint image is set to a threshold value S by the means. After the threshold value S becomes , the time t until the threshold value S becomes (Sl>So)' is measured.

Further, the second measuring means determines that the luminance is equal to the threshold value S.

The elapse of a predetermined time t corresponding to the measurement time t1 is measured after the time t1 is reached.

Then, the fingerprint image obtained by the time t measurement by the second time measuring means is used in the matching process or the registration process.

Effect] People who sweat actively have a short time t, and therefore the general time t required for sweating to become moderate is shorter.

Conversely, people who sweat slowly take a long time t1, and therefore the general time t until sweating becomes moderate is also long.

Since the fingerprint image is read after such a period of time t, it is possible to read the fingerprint image when sweating is moderate and the finger is in close contact with the light guide member, regardless of individual differences in sweating, that is, a clear and A wide range of fingerprint images can be changed.

[Example] (1) One example An embodiment of the present invention will be described based on the drawings.

FIG. 2 shows the configuration of a contact type fingerprint detection device.

The light guide plate IO is, for example, rectangular glass. A laser light source 1 is installed below one end of the light guide plate IO with its radiation surface facing upward.
2 are arranged. Further, a phase type hologram 14 for diffraction is adhered to the lower surface of the other end of the light guide plate IO.

When the finger 16 is pressed onto the light guide plate 10 above the laser light source 12 and the interface between the light guide plate IO and the finger 16 is irradiated with laser light emitted from the laser light source 12, the light guide plate 10 of the finger 16 is irradiated with the laser light. The laser beam is mainly reflected at the close contact portion of the hologram 14, and the lff1 thereof undergoes repeated total reflection, is diffracted downward by the hologram 14, and is guided to the outside.

A two-dimensional image sensor 20 is disposed below the hologram 14 via an imaging lens 18, and a fingerprint image is captured on the image sensor 2.
The image is formed on the imaging plane of 0.

The image sensor 20 is scanned by a drive pulse from the driver 22, and pixel signals are sequentially extracted from the image sensor 20.
This is amplified by the amplifier 24 to become the luminance S, and then binarized by the binarization circuit 26. The binarization threshold is S. It is.

The microcomputer 28 reads the binarized data for each pixel based on the synchronization signal supplied from the driver 22, and writes the fingerprint image into its frame memory. The microcomputer 28 registers the read fingerprint image in the registration memory 32 or compares it with the fingerprint image registered in the registration memory 32 according to the mode set by the mode setting device 30, and determines the processing result. etc. are displayed on the display 34.

A binarization circuit 26B is further connected to the output terminal of the amplifier 24, and the threshold value S1 of this binarization circuit 26B is set to the third
As shown in the figure, it is smaller than the threshold value S of the binarization circuit 26Δ. The RS flip-flop 36 is set by the output of the binarization circuit 26B, and the RS flip-flop 36 is reset by the output of the binarization circuit 26A. With RS flip-flop 36 set, AND gate 38 is opened and clock pulses from clock pulse generator 40 are passed through AND gate 38 and counted by counter 42 . The counter 42 counts the time from when the count value C is cleared by the microcomputer 28 and the output value S of the amplifier 24 becomes 81 until it becomes St. This count value C is read by the microcomputer 28.

Next, the processing procedure in the microcomputer 28 will be explained based on FIG.

(50) The count value of the counter 42 is cleared and the display 3
4, "Please press your finger" is displayed.

When the finger I6 is pressed against the light guide plate IO and the output S of the amplifier 24 becomes S>Sl as shown in FIG. As time progresses to <S>S as shown in FIG. 3(B), the AND gate 38 is closed and time measurement is stopped as described above. Note that FIG. 3 shows the brightness S on the l line of the fingerprint image.

(52) On the other hand, the microcomputer 28 determines that S≧S
(54) The count value C (time 1.) of the counter 42 is read.

(56) Next, “Please keep pressing your finger” appears on the display 34.
is displayed.

(58) Next, the count value C multiplied by a constant is set as the value of the soft timer T, and T is decremented until (60, 62) T = 0. When T=O, that is, a time proportional to the time from the state shown in FIG. 3(A) to the state shown in FIG. 3(B) has elapsed, and the state shown in FIG. 3(C) is reached. (64) The microcomputer 28 converts the binarization circuit 2
A fingerprint image for registration or verification is read from 6A and written to the frame memory y4<.

Here, in FIG. 3, for a person who sweats actively, it takes 1. is short, and therefore the time 11 required for the transition from (B) to (C) is also short; on the other hand, for people who sweat slowly, the situation is opposite to the above. Therefore, in any case, the fingerprint image will be read in a state where sweating has become moderate.

(66) Next, processing according to the mode set by the mode setting device 30, such as fingerprint image registration processing, verification processing, etc., is performed, and the results are displayed on the display 34.

(2) Expansion Note that the present invention includes various other modifications.

For example, the output of the amplifier 24 (rXS is A/D converted, the microcomputer 28 reads it, and the counter 4
The time measurement in step 2 may be performed using a software configuration.

Alternatively, the brightness S of only a partial area of the fingerprint image, for example, an area on a circle, may be compared with the threshold value S8, S.

Also, 1. It is not necessary to have a proportional relationship; further, measure the ambient temperature a and humidity, correct t with these, and generally find t using a function F such as t y=F (t+, aSb). It may be a configuration.

[Effects of the Invention] The contact fingerprint detection device according to the present invention measures the time 1+ from when the brightness of the fingerprint image reaches the threshold S0 until it reaches the threshold S+ (S+>So), and then when the brightness reaches the threshold S1. After the measurement time 1. It is configured to measure the elapse of a predetermined time 11 corresponding to 11, and use the fingerprint image obtained after that in the verification process or registration process. Therefore, the typical time it takes for sweating to become moderate is short, and conversely, people who sweat slowly take time 1. is long,
Therefore, the typical time it takes for sweating to become moderate;
Since the fingerprint image after such a period of time t is used in verification processing, etc., regardless of individual differences in sweating, etc.
A fingerprint image obtained when sweating has become moderate and the finger is in close contact with the light guide member, that is, a clear and wide-ranging fingerprint image, is used, which has the excellent effect of allowing proper registration and verification processing. This greatly contributes to improving the reliability of fingerprint verification.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 to 3 relate to an embodiment of the present invention, in which FIG. 1 is a block diagram showing the hardware configuration of a contact-type fingerprint detection device, and FIG. Flowchart showing the processing procedure. FIGS. 3A, 3B, and 3C are diagrams showing the relationship between the brightness on the 1 line of the fingerprint image and the threshold value. FIGS. 4 and 5 are diagrams showing the relationship between a fingerprint image and a sweating state in terms of the relationship between the brightness on one line of the fingerprint image and a threshold value. In the figure, 10. Light guide plate 2: Laser light source 14: Hologram 16: Finger! 8: Imaging lens 20: Image sensor 22: Driver 24: Amplifier 26: Binarization circuit 28: Microcomputer 30/mode setter 32: Registration memory 34: Display 36: RS flip-flop 38: AND gate 40: Clock Pulse generator 42: counter Hardware configuration of contact type fingerprint detection device Fig. 1 Processing procedure of microcomputer 28 Fig. 2 Location Fig. 3 Fig. 4 Location Explanation of conventional problems Fig. 5

Claims (1)

[Claims] In a contact fingerprint detection device that optically converts the contact state of a finger to the light guide member (10) into a fingerprint image, after the brightness of the fingerprint image reaches a threshold value S_0, a threshold value S_1 (S_1>S_0)
a first time measuring means (
26A, 26B, 36 to 42), and the luminance is the threshold value S_1
After that, a predetermined time t_2 corresponding to the measurement time t_1
Second time measuring means (28, 58 -
62), and the time t_2 by the second time measuring means
A contact fingerprint detection device characterized in that a fingerprint image obtained after measurement is used in a verification process or a registration process.