EP0900427A1

EP0900427A1 - System for acquiring three-dimensional fingerprints and method of acquisition

Info

Publication number: EP0900427A1
Application number: EP97944928A
Authority: EP
Inventors: Henri Thomson-CSF S.C.P.I. RAJBENBACH; Stéphane Thomson-CSF S.C.P.I. SAMOUILHAN; Jean-Pierre Thomson-CSF S.C.P.I. HUIGNARD
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1996-10-04
Filing date: 1997-10-06
Publication date: 1999-03-10
Also published as: FR2754369A1; WO1998015913A1; FR2754369B1; US20020106115A1

Abstract

The invention concerns a system for acquiring three-dimensional fingerprints, characterised in that it comprises: a medium (1) for receiving at least the object whose print is to be taken; optical image recording means (2); means for optical imaging (3) of the surface of the finger on the recording means. This system is applicable for acquiring fingerprints. It comprises various means for immobilising the hand.

Description

RELIEF FINGERPRINT ACQUISITION SYSTEM AND METHOD

ACQUISITION

The invention relates to a system for acquiring raised fingerprints and more particularly to a system for acquiring biometric fingerprints such as fingerprints.

The invention is therefore in the field of optical acquisition of fingerprints and relates to a device for acquiring one or more fingerprints, without contact of the inner face of the finger on the acquisition device. This absence of contact allows acquisition without deformation. The applications relate to fingerprint storage, identification and authentication / validation. There are two types of fingerprint acquisition devices:

1) Ink pads: the person places their finger on an ink pad and then applies it to a sheet of paper in order to transfer the image of the ridges and grooves to a paper support. 2) Camera acquisition: these devices use the principle of frustrated total reflection of a light wave illuminating an optical diopter as described in the documents referenced (1) and (2) at the end of the description. The person applies his finger to an optical prism consisting of a block of glass. The points in contact (the crests of the imprint) disturb the reflection coefficient by a disturbance of the index at the interface diopter. The image of the diopter is transmitted to a camera

(usually a CCD video camera) which thus records the fingerprint.

The main drawbacks of these devices are the quality, reliability and repeatability of the acquisition. Indeed, it is difficult to control the pressure exerted by a person on the paper or the prism. This results in strong distortions of the image of the imprint. This deformation constitutes a major problem for identification operations (search for a person in a database by recognition of fingerprints) and authentication operations (control of the card holder, for example) as described. in the documents referenced 3, 4 and 5 at the end of the description.

To solve these problems, the invention relates to a device for acquiring fingerprints without physical contact from inside the finger on the acquisition device. The acquisition will thus be done in a totally passive phase of the person. The device of the invention therefore solves the problem of image distortions in the acquisition phase.

The invention therefore relates to a fingerprint acquisition system, characterized in that it comprises:

- a support intended to receive at least one finger whose fingerprints must be taken;

- optical image recording means;

optical means for imaging the face of the finger on the recording means.

The various means of this system are described in the claims and in particular, it is provided that the light illuminating the area of the support intended to receive the finger or fingers is polarized and in that the system comprises a polarization analyzer located between the support and the recording means; the analyzer being oriented so that its direction of polarization is parallel or perpendicular to the direction of polarization of the illuminating light.

The invention also relates to a method for acquiring fingerprints characterized in that: - a layer of a material containing metal is deposited on the surface of the finger from which it is desired to take the imprint;

- said surface is illuminated with polarized illumination light;

- The illuminated surface is imaged on the recording means by means of a polarization analyzer whose direction of polarization is parallel or perpendicular to the direction of polarization of the illuminating light.

The various objects and characteristics of the invention will appear more clearly in the description which follows and in the appended figures which represent:

- Figure 1, a general example of implementation of the system of the invention; - Figures 2a to 2j, different embodiments of the support for placing a finger or more, which we want to acquire fingerprints;

- Figures 3a and 3b, arrangements of the system with the support plate in vertical position and oblique position;

- Figure 4, the system according to the invention with artificial lighting;

- Figure 5, the system according to the invention provided for recording fingerprints that have been previously coated with a metal layer;

- Figures 6a to 6d, arrangements of the light source;

- Figures 7a to 7c, the system according to the invention mounted in a housing; - Figures 8a and 8b, an alternative embodiment of the system according to the invention. Referring to Figure 1, we will therefore first describe a simplified embodiment of the system of the invention.

This system comprises a support 1, produced for example in the form of a plate, designed to receive the finger or fingers whose fingerprints must be taken. According to FIG. 1, the face 10 of the support 1 is intended to receive the back of the finger. , the fingerprints to be taken being directed upwards. An imaging device, represented by a lens 2, makes it possible to image the face of the finger carrying the fingerprints on a recording means 3

The fingerprint acquisition device is therefore a contactless device which allows acquisition without deformation of the fingerprints.

The finger (s) whose fingerprints are to be acquired must be correctly located under the imaging device. FIGS. 2a to 2g therefore provide different embodiments of the support 1

According to FIG. 2a, the support produced in the form of a plate 1, has, in its face 10, a groove 1 1 This groove locates the location of the finger laterally with respect to the axis of the finger To position the finger axially, may plan to limit the length of the groove so that the end 12 of the groove corresponds to the end of the finger. The depth of the groove will preferably be provided so that only the nail almost rests on the end 12. The end of the finger will not then undergo deformations which would induce deformations of the imprint.

According to Figure 2b, the groove 11 is a chute the size (in diameter) of the finger. The finger is therefore wedged laterally in this chute.

According to Figure 2c, the walls of the chute are reflective. In addition, the shape of the chute has such a shape, in particular at its upper part, that it can reflect light coming from the side walls of the finger towards the imaging device. Thus one can acquire a more complete image of the imprint. The bottom of the chute then has a shape suitable for wedging the finger while the upper walls of the chute have a curvature allowing reflection of light from the finger towards the imaging device 2.

According to FIG. 2d, the support plate 1 has on its face 10, a stop 13 per finger which it must receive. The end of a finger comes to rest on this stop which allows the finger to be positioned correctly. However, if this stop is such that the end of the finger presses on it, the impression can be deformed.

According to FIG. 2e, the stop 13 includes a space 14 in which the finger nail can slide. In addition, the end 15 of the stopper is tapered so that this end is housed between the nail and the finger. In this way, the impression will not be deformed regardless of the pressure of the finger on the stop.

In the case where the system makes it possible to take the fingerprints of four fingers with one hand, the four fingers must be correctly positioned and all pressed against the face 10 of the plate 1. According to FIG. 2f, a stop 13.1 makes it possible to maintain the major against face 10. For the other fingers, stops 13.2, 13.3 and 13.4 are provided which can slide in grooves 16.2, 16.3, 16.4. These stops are similar to the stop 13 in FIG. 2e and the adjustment of the stops makes it possible to adapt them to different finger lengths. As shown in Figures 2g and 2h, the adjustment system of a stop 13.1 has a T-shaped groove. The stop has a wide part 17.1 placed in the wide part of the T-shaped groove. A spring 18.1 presses the groove 13.1 against the face 10 of the support 1. Along the groove, the face 10 is ridged to slow the movement of the stop. FIG. 2i represents a system for wedging the fingers according to which stops 19.1, 19.2, 19.3 etc. are provided on the support plate, intended to be between the fingers when the hand is placed on the plate 1. The stops can be axially adjustable similar to the stops in Figure 2f. FIG. 2j represents a system of stops comprising a stop 19.2 which serves to call the hand axially between two fingers. The other stops 19.4 to 19.6 serve to align the fingers laterally. For the hand to be properly placed, the patient must press the sides of the fingers against these stops. The stop 19.6 can be common to two fingers (the index and middle fingers for example).

According to an alternative embodiment, the stops can be provided with electrical or mechanical contacts 20.2 to 20.7 (feelers) placed in the contact zones with the fingers. They are symbolized by arrows in Figure 2j. When the hand is properly placed, the contacts are activated by finger pressure and allow the system to operate.

FIG. 3a represents an arrangement of the support 1 oriented vertically with respect to a horizontal base 20. The lens 2 and the recording means are then also arranged vertically. This arrangement is more ergonomic for placing the hand in position against the support 1.

Figure 3b shows a variant of Figure 3a in which the support is inclined relative to the horizontal (for example 30 to 60 °). The hand naturally rests on the support while being retained due to the friction on the support, the optical system 2, 3 is then also inclined to be substantially normal to the plane of the support.

Figure 4 shows a system in which there is provided a light source 4 which illuminates the area 1 1 of the support 1 which is intended to receive a finger. According to FIG. 5, there is provided between the light source 4 and the support 1, a polarizer 5 which makes it possible to illuminate the area 11 using polarized light. There is then provided between the support 1 and the recording means 3, a polarization analyzer 6 oriented in a direction parallel to the direction of polarization of the light transmitted to the area 11.

Such an arrangement is advantageous in the case where it is planned to deposit on the finger, a layer of a product containing a metallic material. The deposition of this product is done so that only the crests of the imprints retain metallic product while the troughs of the grooves do not retain it. It is known to those skilled in the art that diffusion or reflection on a metallic surface occurs with conservation of the direction of polarization;

Consequently, if the analyzer 6 is oriented in the same direction as the polarizer 5, only the image of the peaks of the imprint will be transmitted by the analyzer, which solves the problem of contrast. Alternatively, if the analyzer 6 is oriented in the 90 ° direction from the direction of the polarizer 5, only the image of the grooves will reach the sensitive surface of the shooting device. A device has thus been produced which discriminates peaks and furrows by polarization.

The analyzer 6 has been shown between the lens 2 and the recording means 3, but it can be located between the support 1 and the lens 2.

The light source 4 can be an incandescent lamp, a photographic flash, a halogen lamp or a laser source. In the case of a semiconductor laser source emitting polarized light, the polarizer 5 is not necessary. In addition, the laser source can be a laser emitting in the near infrared.

According to FIG. 6a, several light sources can be provided and in particular the light source can be annular to illuminate the finger from different angles.

Finally, according to FIG. 6b, the light source or sources can be placed so as to illuminate the finger under grazing or almost grazing incidence so as to more effectively view the reliefs of the fingerprint. FIG. 6c represents a system in which an aspherical lens is provided which makes it possible to transmit to the recording medium the image of the sides of the finger

Figure 6d provides for the lighting system a holographic diffuser which receives the light by its edge and diffuses it towards the finger

By using a light source, it is advantageous to subtract the finger whose fingerprint is to be taken from external lighting so that the recording means receive constant lighting. FIG. 7a represents a housing 40 which contains the support 1 with its means for wedging at least one finger such as the chute 1 1, as well as the light source 4 At least one hole 41 is provided in a wall of the housing to allow the passage of at least one finger and its placement in the chute 1 1 Another hole 42 located vertically with respect to chute 1 1, will allow the light reflected by the finger to be transmitted to the imaging device (lens 2) and to the recording means 3 In the case of FIG. 7a, the imaging device and the recording means could be

- a classic camera,

- a digital disc (CD) photo camera,

- a video camera Such a device will then be plated by its lens at hole 42

According to an alternative embodiment shown in FIG. 7b, the support 1, the light source 4, the imaging device 2 and the recording means are mounted in the housing 40 This has the hole 41 for the passage of the at least one finger The recording means 3 are isolated from direct illumination of the source 4 by an internal wall 43 in which the lens 2 is mounted

According to FIG. 7c, provision has been made for the support plate 1 to be mounted in the manner of a drawer in the housing 40. This makes it possible to provide supports 1 interchangeable according to the size of the hands. In FIGS. 7a to 7c, there is no represents only one hole for the passage of a finger but we can provide several holes for several fingers or an elongated hole for the passage of several fingers or for the whole hand In addition, to overcome the apprehension of having to introduce one or more fingers into the holes of a box, provision is made for all or part of the walls of the housing 40 to be transparent For example, as shown in Figure 7c, there will be a window 45 to see inside the housing.

In the foregoing, the imaging device 2 has been described in the form of a lens but it can be produced in the form of: - a macrophotographic objective;

- a macrophotographic objective associated with an aspherical lens adapted to the non-planar shape of the finger, for example a piano-concave lens. The use of such a lens allows the acquisition of a larger imprint surface, in particular the edges of the fingers. These finger edges are important when it comes to extracting characteristics of the imprints, for example the number of

Galton.

The metallic material used in connection with FIG. 5 can consist of a metallic powder (silver, zinc, copper, ...) diluted in a solvent (alcohol, acetone, water ...). This liquid can impregnate a pad of the ink pad on which the finger is placed, or be used in a spray bottle to spray the surface of the finger.

In the case where the device allows the simultaneous acquisition of the fingerprints of several fingers, the support 1 is adapted as described above; the housing has several holes 41 or a hole 41 of elongated shape so that several fingers can slide into the housing; and the field covered by the imaging device 2 will be adapted to the number of impressions to be acquired. The recording means 3 can be a photographic medium such as a photographic negative. They can also be photodetectors. In this case, the photodetectors are preferably arranged in a matrix. Electronic circuits are associated with them for reading the detected signals. For the production of such detectors, CCD circuits available commercially will preferably be used.

According to an alternative embodiment, the recording means can be a matrix sensor produced in CMOS circuits. Each photodetector is associated with a local processing circuit and having connections with neighboring circuits to carry out this processing. This processing notably consists in accentuating the contrast of a photodetector compared to neighboring photodetectors, which will make it possible to obtain a contrasted image of the imprint. For example, when the photodetection current of a first photodetector is greater by a determined percentage than the photodetection currents of second neighboring photodetectors, the system will assign the value 1 to the first photodetector and the value 0 to the second photodetectors.

Such CMOS circuits can be produced as described in the document referenced 6 at the end of the description. An artificial retina detector is also described in the document referenced 7.

The processing of the acquired image can also be digital processing. In particular to accentuate the contrast, we can use a digital filter of the type:

1 -1 -1 -1 -1

1 1 1 1 -1

1 1 9 1 -1

1 1 1 1 -1

1 -1 -1 -1 -1

This filter can be programmed at will to modify the contrast.

Whatever the type of recording means used, the resolution of these recording means may be 128 × 128 (in matrix layout) for a footprint area to be acquired of 3 to 4 cm ² , but it will be difficult to have a lower resolution.

FIG. 8a represents an apparatus making it possible to acquire fingerprints on the two hands of an individual who presents his two hands in the apparatus. This device has two supports 1 and 1 'each similar to that of Figure 3b but inclined in opposite directions. The two supports are illuminated by one or more light sources 4. Above each support a mirror 6, 6 ′ returns the light reflected by the hands to an area located between the two supports. In this area is located a shooting system (2, 3) such as a camera or a photo camera. The light source (s) can take different forms and be placed in different places. According to the example of FIG. 8a, light sources 4, 4 ', 4 "are placed on either side of the mirrors. These sources have reflectors 14, 14', 14" to direct the light towards the supports and possibly masks such as 13 to prevent these sources directly illuminating the shooting system.

The two mirrors 6, 6 'are inclined symmetrically with respect to the axis of the system to reflect light along this axis towards the shooting system. The shooting system is designed to photograph the two supports (both hands) simultaneously or successively. In the case of successive shots, the change of the recording medium 3 (its advancement in the case of a camera or a photo camera) will be done automatically. FIG. 8b represents an apparatus in which instead of the mirrors 6 and 6 ′ is placed the camera system (2, 3). This system is then mounted on an adjustable support so as to be directed at will towards one or the other of the supports 1, 1 '.

In the foregoing, the acquisition of fingerprints has been described, but the system of the invention would allow the acquisition of any biometric imprint, such as the palm of the hand. It would even allow the identification of objects in relief of all kinds such as coins, etc.

The system of the invention has the following advantages: - acquisition of fingerprints without deformation, because without contact of the interior finger surface on the acquisition device;

- possibility of integrating a recognition module into the acquisition device. Indeed, the absence of deformation in the acquisition phase authorizes the use of an electronic module for comparing the acquired fingerprint with one or more fingerprints stored in the device.

This is particularly advantageous in the case of a retina-type detector, because the CMOS-type technology makes it possible to integrate functions of calculation and image processing directly at the level of the sensor. References

(1) A. Shimizu and M. Hase, "Entry method of fingerprint image using prism", Trans. Inst. Electronic. Comm. Engineers Japan, Part D, J67D (5), 627 (1984).

(2) L.A. Gerhardt, J.B. Attili, D.H. Crockett and A.M. Resler, "Fingerprint imagery using frustrated total internai reflection", in Proc. 1986 Int. Camahan Conf. on Security Technology, 251 (1986).

(3) S. Igaki, S. Eguchi, F. Yamagishi, H. Ikeda and T. Inagaki, "Real-time fingerprint sensor using a hologram", Appl. Opt. 31, 1794-1802, (1992).

(4) Jacques Rodolfo, Henri Rajbenbach, Jean-Pierre Huignard, Performance of a Photorefractive Joint Transform Correlator for

Fingerprint Identification, Opt. Eng., 34, 1166 (1994).

(5) H. Rajbenbach, Christophe Touret, J.P. Huignard, "Fingerprint database search by optical correlation", in Optical Pattern Récognition VII, David P. Casasent, Tien-Hsin Chao, Editors, Proc. SPIE 2752, 214-223 (1996).

(6) Carver Mead, "Analog VLSI and Neural System", Editors: ADDISON- WESLEY, 1989, Chapter 15 (Silicon Retina), pp. 257-278.

(7) T. Bernard, B. Zavidaique, F. Devos, IEEE Journal Solid State, 38, 789 (1993).

Claims

1. Acquisition system of relief prints, characterized in that it comprises:

- a support (1) intended to receive at least the object whose imprint must be noted; - optical image recording means (2),

- optical imaging means (3) of the face of the finger on the recording means.

2. System according to claim 1, characterized in that the support is a plate comprising means for wedging the finger laterally and axially (1 1, 12, 13).

3. System according to claim 2, characterized in that the wedging means comprise at least one groove (1 1)

4. System according to claim 2, characterized in that the plate comprises a chute (11). 5. System according to claim 4, characterized in that the surface of the chute is reflective.

6 System according to Claim 2, characterized in that the wedging means comprise a stop intended to position the end of a finger (12, 13) 7 System according to Claim 6, characterized in that the stop (13) comprises a groove (14) intended to receive the end of the nail of a finger

8. System according to claim 2, characterized in that the wedging means comprise stops (19) intended to be located between the fingers

9 System according to claim 8, characterized in that the stops comprise electrical or mechanical contacts for detecting the contact of fingers on the stops

10 System according to claim 2, characterized in that the support plate is oriented vertically or obliquely

1 1 System according to claim 2, characterized in that the support (4) is interchangeable

12 System according to claim 2, characterized in that the wedging means allow the wedging of four or five fingers of the hand 13 System according to claim 12, characterized in that the wedging means allow the wedging of four or five fingers with both hands

14 System according to claim 1, characterized in that the recording and imaging means are located on an axis perpendicular to the plane of the support

15 System according to claim 1, characterized in that it comprises an illumination source illuminating an area of the support intended to receive the finger or fingers. 16 System according to claim 15, characterized in that the light source is a photographic flash lamp, a halogen lamp or a laser source

17 System according to claim 1 5 characterized in that the light source is annular 18 System according to claim 15, characterized in that the light source is intended to light the surface of the finger in grazing light

19 System according to Claim 15, characterized in that it comprises a holographic lighting device 20 System according to Claim 1, characterized in that the recording means comprise a surface of a photographic negative

21 System according to Claim 1, characterized in that the recording means comprise a matrix of photodetectors 22 System according to Claim 20 characterized in that the recording means comprise an electrical processing circuit associated with each photodetector of the matrix

23 System according to any one of claims 1 or 15, characterized in that the imaging means and the recording means are produced using a conventional photo camera a digital disk photo camera or a video camera

24 The system of claim 15 characterized in that the light source and the support are contained in a housing comprising an opening for the insertion of at least one finger and an opening for the transmission of light to the system imagery 25 System according to claim 15, characterized in that the light source and the recording means are contained in a housing comprising an opening for the insertion of at least one finger

26 System according to one of claims 24 or 25, characterized in that the support is in the form of a plate and in that the housing comprises slides in which this plate is slid

27 System according to claim 15, characterized in that the light illuminating the area of the support intended to receive the finger or fingers is polarized and in that the system comprises a polarization analyzer (6) located between the support and the means of recording, the analyzer being oriented so that its direction of polarization is parallel or perpendicular to the direction of polarization of the illuminating light

28 System according to claim 26, characterized in that it comprises a polarizer (5) located between the source and the area of the support 29 Method of acquiring fingerprints characterized in that

- a layer of a material containing metal is deposited on the surface of the finger whose fingerprint is desired to be raised,

- said surface is illuminated with polarized illumination light,

- said illuminated surface is imaged on the recording means by means of a polarization analyzer whose direction of polarization is parallel or perpendicular to the direction of polarization of the illuminating light

30 Method according to claim 29, characterized in that the layer of material containing metal is deposited

- either by applying the finger to a tampon,

- either by rubbing the finger on a material containing metal, - or by vaporizing said material,

- either by applying said material with a brush

31 Method according to claim 29, characterized in that the metal-containing material is produced from a metal powder, such as silver, zinc, copper, this powder being able to be diluted in a solvent