CN1073282A - Photoelectric finger-print recognising instrument - Google Patents

Abstract

The photoelectric finger-print recognising instrument of using Joint conversion principle and liquid crystal light valve have concurrently high capacity that optical imagery handles, fast, the advantage of highly-parallel and Digital Image Processing is able to programme, software function abundant, the characteristics of high precision, easy operating, realize Real time identification with liquid crystal light valve (LCLV) and charge-coupled device (CCD), with Mach-once special interferometer as input block, adopting continuous no-load voltage ratio---the attenuation compensation fingerprint is to seeing through rate variance, and defined special-purpose distinguishing indexes, provide the patterned evaluation result of quantification with the microcomputer digital image processing system.Have in real time, quick, accurate, lower-cost advantage is applicable to that public security, the administration of justice, procurator's office carry out the establishing identity of fingerprint.

Description

Photoelectric finger-print recognising instrument

This invention " photoelectric finger-print recognising instrument " belongs to the information optical Instrument class, and it is applicable to the Real time identification of fingerprint.

In prior art (existing documents United States Patent (USP) 3,771,124 and 3,716,301), the scheme that is used for fingerprint recognition has two classes.The first kind is subjective identification, and this is traditional recognition methods, and shortcoming is subjectivity, uncertainty, and staff's labour intensity is very big, and is time-consuming bothersome.Second class is a machine recognition, also have two kinds of main methods in this identifying schemes, first method is digital picture identification, it is with two fingerprint pattern to be identified CCD(Charge Coupled Device (CCD)) note, become digital picture through after the A/D conversion again, send into computing machine carry out aspect ratio to or pattern-recognition.Because the quantity of information that fingerprint pattern comprises is very big, the digital image system that therefore is used for fingerprint recognition is high capacity, system at a high speed, technical sophistication, and price is higher.The fingerprint on site that some is damaged must be through artificial pre-service before identification, thereby brings subjective factor and uncertain factor into.Second method is to be the optical image recognition of theoretical foundation with the matched filtering.This scheme has two shortcomings that are difficult to overcome: at first be that needs are made matched filter, and require accurately to reset, for operation is made troubles, if reseting precision also can influence recognition effect inadequately.Next is to be difficult to realize Real time identification.Therefore, this method also only rests on laboratory stage up to now, only can be used for teaching and demonstration.

The purpose of this invention is a kind of photoelectricity mixing identifying schemes for the shortcoming that overcomes above-mentioned two methods designs.This invention give full play to the high capacity of optical information processing, fast, able to programme, the high precision of the advantage of highly-parallel and Digital Image Processing, the characteristics that computing function is abundant, the pre-service of fingerprint is very simple, identifying is real-time, software function is abundant, recognition result is reliable, and cost is lower, is easy to instrumentation, is a kind of fingerprint recognition instrument with practical value.

Joint conversion principle is used in this invention " photoelectric finger-print recognising instrument " and liquid crystal light valve is realized, describes design proposal of the present invention and technical characterictic thereof below in conjunction with accompanying drawing:

Fig. 1 is an optical system diagram of the present invention.1 is laser instrument (He-Ne laser instrument or semiconductor laser), laser beam by its radiation is divided into two bundles by continuous no-load voltage ratio spectroscope 3, the angle pencil of ray that a branch of beam-expanding systems formation that constitutes through lens 4 and 6 collimates, inject by reflective mirror 8,10 and the adjustable spectroscope 7 of segmentation, Mach-once special interferometer that spectroscope 14 constitutes, fingerprint negative film 9 and 11 to be identified places two arms of interferometer respectively, stagger mutually apart from 2b about optical axis in their center, and process Fourier transform lens 12 carries out Joint-Fourier transform (hereinafter to be referred as the Joint conversion), here be to adopt the Fourier transform lens 12 of large aperture long-focus as the first time Fourier transform, i.e. Joint-Fourier transform; Adopt the Fourier transform lens 21 of short focal length to make Fourier transform for the second time, obtain relevant output.The focal distance ratio of lens should make the space width of last related output signal and the target surface size of ccd video camera be complementary.And the Joint conversion spectrum is write the input end face of liquid crystal light valve 13.The beam-expanding system that another light beam of being exported by continuous no-load voltage ratio spectroscope 3 is made of lens 15,16 earlier forms the collimated light beam of suitable expansion bundle, after continuously adjustable weakener 18 decay, through spatial filter 19 filtering, adopt the spatial filtering technology to improve the signal to noise ratio (S/N ratio) of output signal.This spatial filter 19 is apertures, and it can be in the plane interscan perpendicular to optical axis, to obtain best effect.Import liquid crystal light valve 13 by polarization splitting prism 20, become and read light.Liquid crystal light valve is to adjust the beam intensity ratio of its write signal and read output signal by continuous no-load voltage ratio spectroscope 3 and continuous adjustable weakener 18, thereby obtains the best identified effect. Reflective mirror 2,5,17 plays the effect that changes beam direction.It is fashionable that input end when 13 has signal to write, because the effect of liquid crystal light valve, convert the Joint conversion complex amplitude spectrum that writes to the Joint power spectrum, read by reading light,, carry out the Fourier transform second time through lens 21 by polarization splitting prism 20, form relevant spectrum, by CCD device 22 records, convert electric signal to, input microcomputer digital image processing system 24.23 and 25 is monitor, respectively coherent signal before the display process and the result after the processing.

The present invention according to Joint conversion carry out fingerprint recognition.If reference fingerprint (archives fingerprint) g ₁(x is y) with fingerprint to be measured (fingerprint on site) g ₂(x, y) place simultaneously input plane (x, y) on, the center after the laser radiation behind the beam-expanding collimation, forms the input signal of system at a distance of 2b:

g（x，y）＝g ₁（x-b，y）+g ₂（x+b，y）， （1）

Promptly compose the Joint conversion complex amplitude spectrum that occurs input signal on the plane at the back focal plane of Fourier transform lens 13:

G ( (u)/(λf ₁,) (v)/(λf ₁) ) = G ₁( (u)/(λf ₁,) (v)/(λf ₁) ) exp [ - j2π ( (ub)/(λf ₁) )]

+ G ₂( (u)/(λf ₁,) (v)/(λf ₁) )exp [j2π ( (ub)/(λf ₁) )], (2)

U, ν are spectrum areal coordinate, f in the formula ₁Be the focal length of lens, λ is a wavelength, G ₁, G ₂Be respectively g ₁, g ₂Fourier transform.G becomes the write signal of the liquid crystal light valve that is positioned at the spectrum plane.

Liquid crystal light valve is the spatial light modulator of light addressing, and it is that the field of liquid crystal causes birefringence effect to the action principle of light wave, writes under the situation that light intensity is lower than threshold value at input face, and its effect is equivalent to a reflective mirror with high reflectance.The light of reading that is imported by polarization splitting prism 20 is plane polarized o light, and through liquid crystal light valve 13 reflections, its polarization state is constant, thereby thoroughly only 20, sees into from the output terminal of system to be details in a play not acted out on stage, but told through dialogues.When the input end face of liquid crystal light valve has the complex amplitude spectrum input of Joint conversion,, make the polarization state of light of reading of incident become e light, thereby can see through polarization splitting prism 15 writing those zones that light intensity surpasses threshold value.Because this effect depends on and write light intensity, thereby what read is the power spectrum of Joint conversion, promptly

$I={\left|G\right|}_2={\left|G_1\right|}_2+{\left|{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="921125836\_DRIMG1.png"\; state="\{\{state\}\}">G</figure-callout>}}_2\right|}_2+G_1\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="921125836\_DRIMG1.png"\; state="\{\{state\}\}">G</figure-callout>}}_2\exp \left[\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="921125836\_DRIMG1.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}\left(\frac{2\mathrm{ub}}{{\mathrm{\&lambda;f}}_1}\right)\right]$ $+G_1{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="921125836\_DRIMG1.png"\; state="\{\{state\}\}">G</figure-callout>}}_2\&CenterDot;\exp [-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="921125836\_DRIMG1.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}\left(\frac{2\mathrm{ub}}{{\mathrm{\&lambda;f}}_1}\right)],\left(3\right)$

When a pair of fingerprint a period of time together, G is arranged ₂=G ₁, substitution (3) formula gets

$I={\left|G_1\right|}_2\{1+\cos [2\mathrm{\&pi;}\left(\frac{2\mathrm{ub}}{{\mathrm{\&lambda;f}}_1}\right)\left]\right\},---\left(4\right)$

The Joint transform power spectrum that shows identical fingerprints is the power spectrum of single fingerprint | G ₁| ²Modulated by the cosine striped.

The read output signal of being represented by (3) formula obtains relevant output through the effect of second Fourier transform lens 2, is presented on the test surface of CCD device 22:

Wherein F.T. { I } represents the Fourier transform to signal I,

The expression related operation, the coordinate of output plane be (ξ, η), ρ=f ₁/ f ₂, f ₂Be the focal length of lens 16, ρ is the zoom factor of figure.(5) in the formula preceding two be g ₁, g ₂Autocorrelation spectrum, overlap in the zero level spectrum; Third and fourth represents g ₁And g ₂Coherence spectra, be distributed in zero level spectrum both sides symmetrically, centre coordinate is respectively (2 ρ b, 0) and (2 ρ b, 0).

If g ₁=g ₂(identical fingerprints), then cross correlation function becomes autocorrelation function, and it has the structure at peak, and promptly relevant peaks locates to present sharp-pointed speck in (2 ρ b, 0) and (2 ρ b, 0).If g ₁≠ g ₂(different fingerprint), then peak value does not appear in cross correlation function.Can differentiate g in view of the above ₁And g ₂The similarities and differences.The CCD device will be correlated with to export and directly be presented on the high-resolution monitor 23.

Light/the write light inlet beam split function of reading of the present invention is realized by continuous variable spectroscope 3.3 optical system as shown in Figure 2.27 is polarization splitting prism, 26 and 26 ' be half-wave plate.Inject the e light transmission 27 in 27 the light wave, o light is anti-by 27.If incident light is a linearly polarized light, then rotate half-wave plate 26, the plane of oscillation of light wave will rotate thereupon, thereby can regulate the beam intensity ratio of e light and o light.Half-wave plate 26 makes the plane of oscillation of the e light of transmission turn over 90 ° becomes o light, guarantees that two bundle output light-waves are concerned with.The beam intensity ratio of reading light/write light inlet that this device can make liquid crystal light valve 100: 1 to 1: 100 on a large scale in scalable continuously.

The light intensity of reading light is again through continuous adjustable weakener 18 decay, and attenuation range is 1～1/30.Weakener is a rotatable glass plate of circle, plates thickness continually varying chromium layer or media coating in one side, another side plating anti-reflection film.

3 and 18 coefficient result, make liquid crystal light valve read light intensity and to write light intensity adjustable continuously on a large scale, guarantee when identification has the fingerprint sample of different transmitances, thereby liquid crystal light valve all is in the power spectrum that its best working point obtains hard contrast, great dynamic range, improves recognition effect.

The present invention adopts the input system of Mach-once special type interferometer as a pair of fingerprint to be identified.It has following function: the first, and fingerprint g ₁And g ₂Place two arms of interferometer respectively, be convenient to change and regulate the operation in orientation; The second, the splitting ratio segmentation of segmentation is adjustable spectroscope 7 is adjustable, from 1: 1-1: 10, thus different beam intensity ratios can be selected, to adapt to g ₁And g ₂Different transmitances, guarantee best recognition effect.

Dedicated microcomputer digital image processing system of the present invention as shown in Figure 3.Adopt the microcomputer digital image processing system to carry out the aftertreatment of related output signal.The fundamental purpose of aftertreatment is make coherent signal graphical, improves the effect directly perceived of identification; And provide one of main foundation that digitized distinguishing indexes assert as fingerprint recognition.This system is made of three parts: the related output signal monitor unit of being made up of CCD device 22 and high resolving power soot-and-whitewash monitor 23, the Digital Image Processing unit and the 386 type microcomputers 33 that are made of video interface and A/D converting unit 28, video memory 29, Display Register 30, main control unit 31, microcomputer interface 32 and colour picture monitor 25.Be divided into two-way by CCD record and converted electric signal: the one tunnel directly sends into monitor 23, uses for the relevant output of visual monitoring; Graphics processing unit is sent on another road, sends into 386 microcomputers after treatment again and carries out aftertreatment, extracts coherent signal, carries out the evaluation of fingerprint homogeneity, and provides the 3 D stereo demonstration of relevant peaks light distribution.

Signal processing flow of the present invention is seen shown in Figure 4 in the accompanying drawing, and the process of its signal processing flow is as follows:

Elementary area initialization → seek in secondary lobe zone relevant peaks → with the peak is that the center is carried out light intensity sampling → average filter → calculating energy concentration degree → determine peak district and background region → homogeneity evaluation index calculating → relevant peaks main body demonstration → data file and filed

The present invention adopts as scheme under going into and carries out the quantitative judgement of fingerprint homogeneity.

(1) peak area definition

Be generally in the area definition simple crosscorrelation district, peak light intensity and surpass 0.5I _MaxThe zone, I wherein _MaxBe largest light intensity in this district.In fingerprint recognition,, in the simple crosscorrelation district, surpass 0.5I owing to reasons such as the breakage of fingerprint on site, distortion _MaxBright spot or the distribution of speck relatively disperse, some bright spots away from the center may not belong to relevant peaks, it (is I that the information of authentic representative fingerprint homogeneity should be distributed in the simple crosscorrelation center _MaxThe position) near the zonule.Therefore, definition encircled energy

$E\left(\mathrm{yo}\right)=\frac{1}{{\mathrm{\&pi;y}}_0^2}{\&Integral;}_{y\&le;}{\&Integral;}_{\mathrm{yo}}\frac{I(\mathrm{\&xi;},\mathrm{\&eta;})}{I\left(\mathrm{0,0}\right)}\mathrm{d\&xi;d\&eta;},---\left(6\right)$

Get I _MaxThe position is a true origin, and it is the center of circle that encircled energy is defined as with the initial point, with γ ₀Be the average intensity in the round territory of radius.Obviously, (ξ, η) in the plane each point light intensity to E(γ ⁰) contribution have weight 1/ γ ²Thereby decentering bright spot far away more is to E(γ ₀) contribution more little.Definition satisfies condition

0.5≤E（γ ₀）≤1 （7）

Point (ξ, set η) is the peak district, is designated as σ ', beyond the peak district, the simple crosscorrelation district is background region with interior zone, is designated as σ ".

(2) signal to noise ratio (snr) definition

$\mathrm{SNR}=\frac{I_{\max }}{\frac{1}{S^{\&prime;\&prime;}}{\&Integral;}_{\mathrm{\&sigma;}}\&Integral;I(\mathrm{\&xi;},\mathrm{\&eta;})\mathrm{d\&xi;d\&eta;}},---\left(8\right)$

Wherein S " is the background region area.So, SNR just represents peak district largest light intensity I _MaxRatio with the background region average intensity.The part that two fingerprints are identical is many more, and then relevant peaks is sharp-pointed more, and SNR is just big more.The sharp-pointed degree of the value representation relevant peaks structure of SNR.

(3) the relevant peaks energy is than definition

$R_{\mathrm{pk}}=\frac{{\&Integral;}_{\mathrm{\&sigma;}}\&Integral;I(\mathrm{\&xi;},\mathrm{\&eta;})\mathrm{d\&xi;d\&eta;}}{{\&Integral;}_{\mathrm{\&sigma;}}\&Integral;I(\mathrm{\&xi;},\mathrm{\&eta;})\mathrm{d\&xi;d\&eta;}},---\left(9\right)$

Wherein σ=σ '+σ " is whole secondary lobe.R _PkEnergy in the expression relevant peaks district and the interior energy ratio in whole relevant districts.The degree that two fingerprints are identical is high more, and then peak district energy is big more, R _PkJust big more.

Experimental results demonstrate that the peak district that redefines is reasonably, signal to noise ratio (S/N ratio) and relevant peaks energy are than the degree that has reflected two fingerprint graph homogeneity from different perspectives comparatively truly.

The finger-print recognising instrument of making according to above-mentioned design proposal, owing to adopted photoelectricity mixings identifying schemes, have concurrently high capacity that optical imagery handles, fast, the advantage of highly-parallel and Digital Image Processing is able to programme, software function is enriched, the advantage of high precision, easy operating.This invention is the conversion identification of being correlated with according to Joint, and replace hologram recording material with liquid crystal light valve, carries out the interface conversion of light, electric treatment system with CCD, thereby realized Real time identification; Make operation convenient with Mach-once special interferometer as input system; Adopt continuous variable spectroscope and continuous adjustable weakener to compensate the difference of fingerprint on site and archives fingerprint transmitance, guarantee the recognition effect that reaches best; The degree that the distinguishing indexes signal to noise ratio (S/N ratio) of special definition and relevant peaks energy have reflected a pair of fingerprint homogeneity more exactly; Microcomputer image processing system provides abundant software function, has provided digitizing, patterned homogeneity evaluation index.This invention has in real time, quick, convenient, accurate, reliable characteristics, and low public security, the administration of justice, the procurator's office of being applicable to of price judged as the homogeneity of fingerprint.

Embodiments of the invention visible Fig. 1-3.Wherein the He-Ne laser instrument can adopt the 10mw external cavity type, and it is that 670nm, output power are the device of 10nm that semiconductor laser can adopt wavelength; Fourier transform lens 12 should adopt focal length 〉=1000mm, aperture 〉=100mm, and the focal length of another Fourier transform lens 21 is 100mm, and the aperture is 20mm; Collimated light field diameter after lens 4,6 expand bundle should be greater than fingerprint to be measured (135 negative film) more than the size twice; CCD 22 should adopt the device of high resolving power (for example 604 * 588 pixels), low-light (level) (minimal illumination is 0.02Lux); Microcomputer can adopt PC-286,386 types; The spatial frequency of liquid crystal light valve should be not less than 60 lines right/mm.

Description of drawings:

Fig. 1 optical system diagram

1 laser instrument (He-Ne laser instrument or semiconductor laser)

2,5,17 reflective mirrors

3 continuous no-load voltage ratio spectroscopes

4,6 beam-expanding systems

The adjustable spectroscope of 7 segmentations

8,10 reflective mirrors (large aperture)

9,11 fingerprints to be measured (135 negative films, band frame)

12,21 Fourier transform lenses

13 liquid crystal light valves (LCLV)

14 spectroscopes

18 continuous adjustable weakeners

19 spatial filters

20 polarization splitting prisms

22 Charge Coupled Device (CCD) (CCD)

23 high-resolution black-and-white monitors

24 microcomputer digital image processing systems

25 high-resolution color monitors

Fig. 2 continuous variable spectroscope optical system diagram

26 half-wave plates

27 polarization splitting prisms

Fig. 3 microcomputer digital image processing system block diagram

28 video interfaces and A/D converting unit

29 video memories

30 Display Registers

31 main control units

32 microcomputer interfaces

33 microcomputers (386 or 286)

Fig. 4 signal processing flow figure

Claims (7)

1, the photoelectric finger-print recognising instrument that contains Charge Coupled Device (CCD), digital image system, optical information processing system, it is characterized in that it being two fingerprint negative films to be carried out the liquid crystal light valve of Real time identification identification as Joint conversion complex amplitude spectrum and power spectrum switching device by having adopted, fingerprint image input system, spatial filter, photoelectric commutator and microcomputer digital image processing system constitute.

2,, it is characterized in that liquid crystal light valve is a beam intensity ratio of being adjusted its write signal and read output signal by continuous no-load voltage ratio spectroscope 3 and continuous adjustable weakener 18 according to the described photoelectric finger-print recognising instrument of claim 1.

3, according to claim 1,2 described photoelectric finger-print recognising instruments, it is characterized in that its relevant output light signal is to adopt the Fourier transform lens 12 of large aperture, long-focus to make Joint-Fourier transform for the first time, and the Fourier transform lens 21 that adopts short focal length is made Fourier transform for the second time, obtain relevant output, and with the electrooptical device of Charge Coupled Device (CCD) (CCD) as related output signal.

4, according to the described photoelectric finger-print recognising instrument of claim 1, it is characterized in that fingerprint image input system is to adopt Mach-once special interferometer, two fingerprint negative films are placed interferometer two arms respectively, and first spectroscope of interferometer is to adopt the adjustable spectroscope 7 of segmentation.

5, according to the described photoelectric finger-print recognising instrument of claim 1, it is characterized in that spatial filter 19 is small filters, it can be in the plane interscan perpendicular to optical axis.

6,, it is characterized in that the microcomputer digital image processing system is provided with as graphical, the digitized aftertreatment of related output signal, has three monitors according to the described photoelectric finger-print recognising instrument of claim 1:

A, high-resolution black-and-white monitor 23 directly show coherent signal by CCD conversion back;

B, high-resolution color monitor 25, the image after the display process;

The monitor of c, microcomputer, display menu and working procedure.

7, a kind ofly carry out the quantitative judgement method of fingerprint homogeneity, it is characterized in that signal to noise ratio (S/N ratio) and relevant peaks energy than being the index of judging fingerprint homogeneity by photoelectric finger-print recognising instrument:

A, definition average intensity in the round territory of relevant peaks surpass peak value 1/2 for the circle of threshold value is the scope in relevant peaks district, define beyond the relevant peaks district, being correlated with, to distinguish with all the other interior zones be background region;

The ratio of light intensity and the average intensity of background region of b, definition relevant peaks is a signal to noise ratio snr, and its value is big more just to indicate that the identical part of two fingerprints is many more, and relevant peaks is just sharp-pointed more;

The luminous energy in c, definition relevant peaks district compares R with the ratio of total luminous energy in relevant district for the relevant peaks energy _Pk, two fingerprint same degree are high more, and peak district energy is big more, and then the relevant peaks energy is than also just big more.

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