CA2094599A1 - Fingerprint imaging - Google Patents
Fingerprint imagingInfo
- Publication number
- CA2094599A1 CA2094599A1 CA002094599A CA2094599A CA2094599A1 CA 2094599 A1 CA2094599 A1 CA 2094599A1 CA 002094599 A CA002094599 A CA 002094599A CA 2094599 A CA2094599 A CA 2094599A CA 2094599 A1 CA2094599 A1 CA 2094599A1
- Authority
- CA
- Canada
- Prior art keywords
- light
- fingerprint
- direct image
- major surface
- transmitting member
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
- G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
- G06V40/12—Fingerprints or palmprints
- G06V40/13—Sensors therefor
- G06V40/1324—Sensors therefor by using geometrical optics, e.g. using prisms
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Human Computer Interaction (AREA)
- General Physics & Mathematics (AREA)
- Multimedia (AREA)
- Theoretical Computer Science (AREA)
- Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
- Image Input (AREA)
Abstract
2094599 9211608 PCTABS00014 A direct fingerprint image is formed by illuminating a transparent planar substrate (22) from one surface (26) with collimated light (20), the substrate (22) having pressed against the other surface (28) a fingerprint (30) to be imaged. Light striking the surface (26) against which ridges of the fingerprint (30) are in contact undergoes total internal reflection within the substrate (22) and causes a direct image of the fingerprint to be formed by generating fluorescent light within a planar fluorescent member (38).
Description
W 0')2/1~60~ LL~ L~ ' ~ PCT/GB91/02295 The pre~ent invention relates to apparatus and a method for fingerprint ima8ing.
Methods and apparatus for fingerprint characterl~atlon are well ~nown and generall~ require an image of n fingerprint to be formed, either electronically or phy~ically, thi~ for~ed lmage being the bas~ of the chasacteri~ation tech~ique. In order for the characterisation to be effecti~e ~nd a~ sccurate afi possible it i6 a requirement that the i~age of th~ fingerpr~nt 80 formed be as sharp as pos~ible and that there be hlgh contra~t a~
10 between the ridgec and reces~e~ pre~ent in the actual ~`
fingerprint. The Applicant's present UR Patent Application number 9006370.2 discloses a fingerprlnt characteri6st~0n technique which relie~ on such ao l~age.
- Various ~ethods have been propo~ed for for~ing such 15 high-contrast, ~oot defl~ition ~age~. One 2xa~ple i6 Europea~ ~
Patent Application, publication number 0,348pl82. Thi8 ~.
discloses a system havlng a transparent base with upper and lower surfaces. The upper eurface defines a contact portion again~t which i8 placed the fingerprint to be i~aged. Light i6 incident, via the transparent base, upon this portlon. Some of the light strike6 those areas of the contact portion, above which are recesses in the fingerprint, and is then reflected back toward the lower surface and out of the bace. Some light, however, ~trikes other areas of the contact portion abo~e and in contact with which i~ a ridge of fingerprint. The light stri~ing these other areas i~ diffusely reflected or scattered and some oi thi~ wlll undergo total internal reflection within the base. Thi6 totally internally reflected light ia then drawn out of ehe transparent base via a lens and enters ~n ~mage , 30 sensor.
A similar method is employed by European Patent Application, publication number 0,194,783. Once again, the~ -' J, light which is used to form the image is that which is diffuselyscattered or reflected from the portion of the transparent plate -~ 35 which ib in contact with the fingerprint ridge= and then ~
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W O 92/ll608 : 2 : PCT/GB91/02295 ~j:, undergoea total lnternal refloction within the trAnsparant plate. Thi6 6ystem also requlres ~ome form of optlcal element, for exaMple, a hologram, to guide this light out of the trAnsparent plate and on to an $mage detector.
Such ~y6tem~ ~uffer from having to rel~ on the dlffu~ely scattered or reflected li~ht fro~ the finger rldges to contrast with the absence of such ~here the inter-ridge gaps exist in order to for~ the final ima~e. ~o~e~er, it i8 po~sible for light to be ~catter¢d into the ~nter-ridge areas, and then back into the tran~port platc, thu~ creating the sa~ç effect as the presence of ~ ridge (scatterine and r~flection) ~here no ridge is present. As a consequence! images 80 obtained tend to suffer poor contrast and appear as pin~ on grey rather thaD black on white for a good contrast image.
In add~tlon, any re~dues of ~k~n or 8reas~ remalnlng UpOD
the contact port~o~ of the tr$n~parent plate tend eo scatter `, sufficient incident l~ght 80 as to prod~ce latent images which carry over to subsequent images and degrade their quality.
Furthermore, such sy~tems do not produce a direct ima8e of ~; 20 the fingerprint. They re~uire further optical equipment to i intercept the totally ~nternully reflected light and to utilise this light in order to produce a v~ewable image.
It ifi thUR an object of the present invention to provide a method of producing ~n image of a fin~erprlnt ~hcrein the ~ma8e ~i 25 i6 a direct image, that is, the image may be vie~ed without the `- aid of optical equip~ent, snd wherein the ~m~ee ~o produced i~
~`~ of substantially increased contra6t as conpared to the prior art ~ devices, making the lmage particularly suitable for use in the -~ Applicant's aforement~oned co-pending application, No. 9006370.2. `
It ~6 a further object of the present invention to provide apparatu~ for producing ~uch an image. ~`
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Hence, according to a fir~t ~pect of the present invention there is provided a method for for~in~ a direct i~age of a ` fingerprint, the method comprl6ing; introducing collimated light into a light tran6mitting member having first and ~econd parallel major surface~ such that the light lnterac~6 with the ` ::
. , : . ' : . . , , , . :
W O ~2/11608 ~ ! PCT/GB91/0229 firse ma~or surface thereof, in contact ~th whlch $8 a fingerprint to be imaged, the light then reflecting from the first major surface towards the 6econd ma~or surface, optically coupled with which i8 a direct i~a8e producing means, thereby to form a direct image of the flngerprint. Thus the need for a detector or other optical equipment receptlve to diffu6ely scattered or reflected light thereby to produce an ~aBe is obY~ated becau6e a directly viewable ima~e i8 pr~duced. Becau6e both the fingerprint and ~mage thereof lie in parallel planes by virtue of the parallel ~a~or surfaces of the light transmitting ~eans, there is no requirement for compen6stion of'kerbstone' distortion and no need for a large depth-of-field in the image detector means as is the case with prior-art non-direct image formation method6. The term 'kerbstone' distortion (which i8 introduced by obliquely viewing an ob~ect) will be as~umed to be understood by persons skilled in this art.
-~ According to a second a~pect of the present invention there i8 provided apparatus for Por~ing a direct image of a fingerprint comprising a light transmlttin8 member hsvin~ a first major surface for receiving a fingerprint and a second major surface, arranged 6ub~tantially parallel to the fir~t ma~or ~urface and ~n optical cooperation with a tirect image producing means, the apparatus arran8ed for receiving collimated light ~ia the second ma~or surface ant reflecting from the first major 6urface thereby to produce 8 direct image of a fingerprint.
Preferably the dlrect image producing meana comprises.a light scattering surfsce ~uch as a ~rsund glass plate member or the like or a very thin layer of paint which i8 non-opaque, or ~-` the like. So long a~ the direct ~ma8e produc~ng means i6 3U optically-coupled with the light transmitting member, that is, their respective refractive indices match, or they are coupled `~ to~ether uslng ~nown refractive index matching means, such as a ~` suitable gel, oil or adhesive, then the iDage producing means i8 receptive to light impinging thereon and acts as a back- ~-projection viewing screen or "secondary" light source.
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W O 92/ll6UX 4 PCT/GB91/02295
Methods and apparatus for fingerprint characterl~atlon are well ~nown and generall~ require an image of n fingerprint to be formed, either electronically or phy~ically, thi~ for~ed lmage being the bas~ of the chasacteri~ation tech~ique. In order for the characterisation to be effecti~e ~nd a~ sccurate afi possible it i6 a requirement that the i~age of th~ fingerpr~nt 80 formed be as sharp as pos~ible and that there be hlgh contra~t a~
10 between the ridgec and reces~e~ pre~ent in the actual ~`
fingerprint. The Applicant's present UR Patent Application number 9006370.2 discloses a fingerprlnt characteri6st~0n technique which relie~ on such ao l~age.
- Various ~ethods have been propo~ed for for~ing such 15 high-contrast, ~oot defl~ition ~age~. One 2xa~ple i6 Europea~ ~
Patent Application, publication number 0,348pl82. Thi8 ~.
discloses a system havlng a transparent base with upper and lower surfaces. The upper eurface defines a contact portion again~t which i8 placed the fingerprint to be i~aged. Light i6 incident, via the transparent base, upon this portlon. Some of the light strike6 those areas of the contact portion, above which are recesses in the fingerprint, and is then reflected back toward the lower surface and out of the bace. Some light, however, ~trikes other areas of the contact portion abo~e and in contact with which i~ a ridge of fingerprint. The light stri~ing these other areas i~ diffusely reflected or scattered and some oi thi~ wlll undergo total internal reflection within the base. Thi6 totally internally reflected light ia then drawn out of ehe transparent base via a lens and enters ~n ~mage , 30 sensor.
A similar method is employed by European Patent Application, publication number 0,194,783. Once again, the~ -' J, light which is used to form the image is that which is diffuselyscattered or reflected from the portion of the transparent plate -~ 35 which ib in contact with the fingerprint ridge= and then ~
.1 .
,: , ~ : , .
. , : :, ~
9 ,~
W O 92/ll608 : 2 : PCT/GB91/02295 ~j:, undergoea total lnternal refloction within the trAnsparant plate. Thi6 6ystem also requlres ~ome form of optlcal element, for exaMple, a hologram, to guide this light out of the trAnsparent plate and on to an $mage detector.
Such ~y6tem~ ~uffer from having to rel~ on the dlffu~ely scattered or reflected li~ht fro~ the finger rldges to contrast with the absence of such ~here the inter-ridge gaps exist in order to for~ the final ima~e. ~o~e~er, it i8 po~sible for light to be ~catter¢d into the ~nter-ridge areas, and then back into the tran~port platc, thu~ creating the sa~ç effect as the presence of ~ ridge (scatterine and r~flection) ~here no ridge is present. As a consequence! images 80 obtained tend to suffer poor contrast and appear as pin~ on grey rather thaD black on white for a good contrast image.
In add~tlon, any re~dues of ~k~n or 8reas~ remalnlng UpOD
the contact port~o~ of the tr$n~parent plate tend eo scatter `, sufficient incident l~ght 80 as to prod~ce latent images which carry over to subsequent images and degrade their quality.
Furthermore, such sy~tems do not produce a direct ima8e of ~; 20 the fingerprint. They re~uire further optical equipment to i intercept the totally ~nternully reflected light and to utilise this light in order to produce a v~ewable image.
It ifi thUR an object of the present invention to provide a method of producing ~n image of a fin~erprlnt ~hcrein the ~ma8e ~i 25 i6 a direct image, that is, the image may be vie~ed without the `- aid of optical equip~ent, snd wherein the ~m~ee ~o produced i~
~`~ of substantially increased contra6t as conpared to the prior art ~ devices, making the lmage particularly suitable for use in the -~ Applicant's aforement~oned co-pending application, No. 9006370.2. `
It ~6 a further object of the present invention to provide apparatu~ for producing ~uch an image. ~`
.;~
Hence, according to a fir~t ~pect of the present invention there is provided a method for for~in~ a direct i~age of a ` fingerprint, the method comprl6ing; introducing collimated light into a light tran6mitting member having first and ~econd parallel major surface~ such that the light lnterac~6 with the ` ::
. , : . ' : . . , , , . :
W O ~2/11608 ~ ! PCT/GB91/0229 firse ma~or surface thereof, in contact ~th whlch $8 a fingerprint to be imaged, the light then reflecting from the first major surface towards the 6econd ma~or surface, optically coupled with which i8 a direct i~a8e producing means, thereby to form a direct image of the flngerprint. Thus the need for a detector or other optical equipment receptlve to diffu6ely scattered or reflected light thereby to produce an ~aBe is obY~ated becau6e a directly viewable ima~e i8 pr~duced. Becau6e both the fingerprint and ~mage thereof lie in parallel planes by virtue of the parallel ~a~or surfaces of the light transmitting ~eans, there is no requirement for compen6stion of'kerbstone' distortion and no need for a large depth-of-field in the image detector means as is the case with prior-art non-direct image formation method6. The term 'kerbstone' distortion (which i8 introduced by obliquely viewing an ob~ect) will be as~umed to be understood by persons skilled in this art.
-~ According to a second a~pect of the present invention there i8 provided apparatus for Por~ing a direct image of a fingerprint comprising a light transmlttin8 member hsvin~ a first major surface for receiving a fingerprint and a second major surface, arranged 6ub~tantially parallel to the fir~t ma~or ~urface and ~n optical cooperation with a tirect image producing means, the apparatus arran8ed for receiving collimated light ~ia the second ma~or surface ant reflecting from the first major 6urface thereby to produce 8 direct image of a fingerprint.
Preferably the dlrect image producing meana comprises.a light scattering surfsce ~uch as a ~rsund glass plate member or the like or a very thin layer of paint which i8 non-opaque, or ~-` the like. So long a~ the direct ~ma8e produc~ng means i6 3U optically-coupled with the light transmitting member, that is, their respective refractive indices match, or they are coupled `~ to~ether uslng ~nown refractive index matching means, such as a ~` suitable gel, oil or adhesive, then the iDage producing means i8 receptive to light impinging thereon and acts as a back- ~-projection viewing screen or "secondary" light source.
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' .' ' , ' : : ~: ~ ' , , . . ,, , : :
, .......... : . . . . ., , . , : . . . . ,:
:::-: . . .. : :::: : -,........ , : . : :
W O 92/ll6UX 4 PCT/GB91/02295
2 0 ~ ~ ~ 9 9 '` 6' Alternatively or add~tionally the dlrect lm~ge produc~ng means comprise~ fluore~cent material. Thi6 may take the form of a dye-doped pla6t~ C8 materlal.
Prefersbly the collimated l~ght 18 introduced into the ; 5 light tran~mitting member via a prism means. Ad~antageously light is reflected from the fir~t major surface toward the cecond major surface by tot~l inter~l reflectlon.
The inve~tlon ~ill now be described, by way of ex~ple only, ~ith refere~ce to the following drawing~ of which;
Figure 1 6hows a schematic representation of a prior srt fingerprint i~aging device;
Figure 2 shows a schematic repre~entstion of a first embodime~t of the pre~ent invention;
; ~igure 3 shows a schematic representation of a further 15 embodiment of the pre6ent inYention;
Figure 4 showe a sche~atic illustration of yet a . further embodlment of the pre~ent in~e~tion, and;
Figure 5 ~how6 a schematic illustration of yet a further embodiment of the pre6ent in~ention. ~.
Referring firstly to Figure l a :Li8ht source 2 is effective to illuminate a transparent plate 4. In contact with the plate 4 ~8 a fin~erprint characterlsed b~ r:Ldge6 6 and rece6ses 8, the ::` ridges 6 being in contact with the sur~ace of plate 4 and the rece~ses 8 being spaced from the surface of plate 4 by a ~eries of air gap6. Light entering the plate 4 i6 randomly reflected by the r~dges 6 ~nd i8 thereby scattered in all direction~, ince an air gap i6 not formed at ridge6 ~. Scattered light ~ beams lO which ~ati6fy the total internal reflection condition, ;:. that is 9 have an angle of inc~dence greater than the critical angle, are totally reflected by the lower gurface of plate 4.
. Such bea~6, only one of which l6 shown in Figure l, are then totally reflected by the lower ~urface of plate 4 ant then, ;l following one or more further total internal reflections at upper and lower surfaces, pa86 through some form of optical element 12, for example a hologram or lens, to be detected by an image sensor 14 arr~nget out~lde of the tran6parent plate 4.
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:; - . ~ , `', ' ~ ' ~ ' ~ - ' :' :: :' : , . ~ , W O 92/l160~ : 5 a PCT/GB91/02295 This i~ nece6sary becau6e the sy~tem does not form a direct imaBe of the fingerprint.
Alternatively light from lJght ~ource 2 ~ay be arranged to 6trike the upper internal ~urface of plate 4 at n angle of incidence greater than the critical angle; in ~hich ca6e light ~trik~ng the surface in ~re~ ~bove ~hich 1~ a rece~s 8 will be totd ly reflected, wh~lst li~ht istri~ing the ~urface in areas at which i8 a ridBe 6 wlll be partially absorbed due to a change i~
the critical angle a6 a result of a modified index of refraction due to the contact of the ridge 6 with the plate 4 ~urface.
Figure 2 ~llu6trates one embodiment of the present invention wherein relatively poor contrast i~ages9 as are obtained by ~uch devices as shown in Figure 1, are at lea~t slleviated.
The o~bodi~ent in Figure 2 compri~e~ ~ light source 16 and collimating lens 18 arranged to produce a broad coll~ated light bea~ 20. Thi8 light 20 is introduced into a l~ght transmltting member 22, which is in the form of a transparent 6ubstrate ~uch as a gla~s or plastics plate, ~la a prism means 24 such as a j 20 glas~ pri~m optically coupled to one ~ajor surface 26 of the light transmitting member 22 by a refractive index coupling mediu~. Alternatlvely, the prism 24 can be formed integrally with the light transmitt~ng member 22.
A second ma~or 6urface 28 of the light tran6mitting member 25 i5 arranged parallel to msjor surface 26. A~ain6t the 6econd major surface 28 i6 held a fiuger 30 from which a fingerprint image i6 to be obtained. It is to be under6tood that the expre6sion "fingerprint" i8 to include all anato~ical attribute6 characteristic of an individual which are suEceptible to the present method 6uch a~ thumb-prints, palm-print6 and foot-print6. The finger is cho6en ~imply a~ lt i8 the mo~t convenient by way of example.
The angle of incidence, q, at ~hich the collimated light 20 6trike~ the upper ~urface Z8 again6t which is placed the finger 30 is arranged to be greater than the critical angle for the medium from which the light tran6mitting member 22 i~
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W 0 92/l160# ~ rj ~ ~J 6 : PCT/GB91/022 fon~ed, Aueh as by approp~ately pos~tlon~n~ the light source 16 relative to that area of the major surface 28 desiBnated to recelve the finger.
This mesn6 that light 20 ctriking a point on the ~urface 28 above which ia a reces6 32 of the fi~gerprint ~ill be totally internally reflected, as ~hown schematically by reflected light ray 36, to~ards lo~er surface 26. Light 20 strik$~8 surf~ce 28 in those areas in con~act wlth ~hlch i8 a fineerprlnt ridge 34 will be largely absorbed, scattered and dlffusely reflected, as shown 6chematically by reflected lIght ray 36a, to~ards lower surface 26 but with reduced inten~ty as a result of such processeR.
A direct image producing means 38, in the for~ of a transparent fluorescent pla6tics layer material, is in op~ical cooperation with the lower aurface 26 of ~e~er 22. The dlrect ; image produclng means 38 need not be in direct contsct with ~urface 26, in which case some form of refractive index coupling medium may be required.
Reflected light 36 passes through the light tranfimitting i 20 member 22 via lower surface 26 and impinge6 upon the direct image producing 0eans 38. The reflected light 36 ~8 spatially modified as compared with the incident light 20 due to the ` spatially dependent ab60rption proce~ses ~hich occur ~here the light is internally reflected at the upper 6urface 28 cau6ed by the pressure of ridges 34.
~ The fluore6cent dye within the direct image producing means $ 38 absorb6 the reflected llght 36 incident thereon within a `~ ~pecif~c wavelength ra~ge (governed by the fluoresce~t dye) ant then re-emits light 40 in a characteristic (of the dye) narrow, longer-wavelength rangel a~ determined by the fluorescent dye.
`~ The spatial modulation at this stage is unaffected, that is, the ~`. image of the light is unchanged as between that of the fingerprint on upper surface 28 and that produced by the direct image produclng means 38.
Fluorescence of the dye in the direct image producing ~eane - 38 may be enabled not only by the wavelength characteristics of .
,':`.' , WO 92J1 160X ~ U ~ ~ r~ ~ 3 PCT/GB91/02295 the inc~dent llght, but alao by the intensity of thls light. It will be apparent that those components of reflected light 36 which have undergone total internal reflection at upper 6urface 28 are of greater intensity than those components of reflected . 5 light 36a which have been largely absorbed, scattered and diffusely reflected from upper surf~ce 28. ~ence, by suitable choice of in~tial light 16 inten~ity, and tran~mi~cion coeff~clent~ of the d~rect ~mage producing mesns 387 It i~ pos6ible to arrange for the absorbed,scattered and diffu~ely reflected l~ght 36a to be of insufficient 6ignificant ~ntensity to cause fluorescent within the direct i~age producing means 38.
Thus the image produced will ha~e light areas ~caused b~
fluore6cence) corresponding to those points on the upper surface 28 underlying fingerprint recesses 32; and dark area~ (cau6ed by non-fluorescence) corresponding to those points on the upper surface 28 in contact with fingerprint ridges 34. It will be sppreciated that there will be high contrast between these light and dark areas as compared with prior art devices. Because the lower surface 26 and upper ~urface 28 of the light tran6mittin8 - member 22 are parallel, then lt will be seen that if the direct image producing means 38 is planar, then the plsne of emission of light 40 egre6slng from the direct lmage produc~ng means 38 `~ i8 parsllel to the obje~t plane that 18, the upper surface 28.
This means that there wlll be no spatial distortion between the fingerprint and its fluorescent image, thus obvlating ~ .
'kerbstone' and a~sociated unwanted image distortion effects which would require &nnmorphic correction or compensstion.
Furthermore, because the fluorescence of the ima8e producing means 38 acts in effect as a bac~-projectlon viewing screen or 'secondary' light source, then the image so produced - is a direct image, which means it may by viewed by eye or a video camera 42 or the like. There i6 no optical processing .. required to view the image produced in this way. The si7e ratio of image to subject in the present invention is intrinsically ,.. , 1:1.
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W 0 92/l160#~ 3 ~ 8 : PCT/GB91/022 Referring now to Figure 3, wherein similar component6 to that of Figure 2 are like numbered, an alternative embodiment of the present invention i~ illustrated.
In this alternative embodiment, the colli~ated light 20 i6 introduced into the light transmitting member by wsy of a priæm means in the form of a Fresnel priam strip 44. This allows for a more compact device than the previous de8cribed embodiment - employing a prism 24.
Also, Figure 3 details tbe lmage producing means bein8 in the form of a ground glas~ plate 46 or thin layer of non-opaque paint applied to the 6urface 26. Whilst thi~ form of image producing means does not work by fluorescence, the ground glass plate 46 6catters or diffuses the reflected light 36 incident thereon and hence al~o produces a direct image of the fingerprint.
Figure 5 illustrates a further embodiment of the present i invention in which the spatially modulated light 36, 36a i~
permitted to undergo a further total internal reflection at surface 26 before being imaged onto the ground glas6 plate 46.
In this case, the direct image produced is viewed by video camera 42 from lower surface 26 via the light transmitting member 22. Thi6 particular embodiment allow6 for the finger- `
' placement surface to be laterally displaced from the imaging ; screen thereby providing for a compact imaging sy~tem.
It will be appreciated by those 6killed in thi6 art that the present in~ention pro~ides a compact, relatively slim imaging system by suitable choice of the optical component~
described herebefore.
Furthermore, it will be appreciated that the po6sibility ~- 30 exists of providing low-co~t replaceable light transmitting members which may be discarded after a certain amount of use due to the build-up of grease or other deposits on the upper surface thereof Such grease (and dirt) i~ inherent within any skin.
` Also it is possible to overlie the upper surface of the light -' 35 transmitting member with a '~croll' of transparent material or ~ the like such that a fresh ~urface ~ay be presented to each , .
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W 0~)2/116()~ : 9 : PCT/GB91/02295 ., flngerprint, as shown in Figure 4.
It will be apparent to tho~e ~killed in the art that by producing a direct image, the imAge plQne, thst iB the fluore6cent pla6tics layer or ground glass or the like i~
acce6sible. ~ence, any optical calibration which may be required, for example ali~nment of video c~mera 42 ~ay be achieved by simply inserting 60me form of reference grid or "test card" over the direc~ ima~e plane.
It will al80 be appreciated that the present invention ~:
requires no focussin6 or correction elements or the like due to the formation of a direct image. Furthermore, because the invention i~ relatively simple optically, alignment procedure6 :nd a66e=bly c06t6 are nrt extens1ve.
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Prefersbly the collimated l~ght 18 introduced into the ; 5 light tran~mitting member via a prism means. Ad~antageously light is reflected from the fir~t major surface toward the cecond major surface by tot~l inter~l reflectlon.
The inve~tlon ~ill now be described, by way of ex~ple only, ~ith refere~ce to the following drawing~ of which;
Figure 1 6hows a schematic representation of a prior srt fingerprint i~aging device;
Figure 2 shows a schematic repre~entstion of a first embodime~t of the pre~ent invention;
; ~igure 3 shows a schematic representation of a further 15 embodiment of the pre6ent inYention;
Figure 4 showe a sche~atic illustration of yet a . further embodlment of the pre~ent in~e~tion, and;
Figure 5 ~how6 a schematic illustration of yet a further embodiment of the pre6ent in~ention. ~.
Referring firstly to Figure l a :Li8ht source 2 is effective to illuminate a transparent plate 4. In contact with the plate 4 ~8 a fin~erprint characterlsed b~ r:Ldge6 6 and rece6ses 8, the ::` ridges 6 being in contact with the sur~ace of plate 4 and the rece~ses 8 being spaced from the surface of plate 4 by a ~eries of air gap6. Light entering the plate 4 i6 randomly reflected by the r~dges 6 ~nd i8 thereby scattered in all direction~, ince an air gap i6 not formed at ridge6 ~. Scattered light ~ beams lO which ~ati6fy the total internal reflection condition, ;:. that is 9 have an angle of inc~dence greater than the critical angle, are totally reflected by the lower gurface of plate 4.
. Such bea~6, only one of which l6 shown in Figure l, are then totally reflected by the lower ~urface of plate 4 ant then, ;l following one or more further total internal reflections at upper and lower surfaces, pa86 through some form of optical element 12, for example a hologram or lens, to be detected by an image sensor 14 arr~nget out~lde of the tran6parent plate 4.
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:; - . ~ , `', ' ~ ' ~ ' ~ - ' :' :: :' : , . ~ , W O 92/l160~ : 5 a PCT/GB91/02295 This i~ nece6sary becau6e the sy~tem does not form a direct imaBe of the fingerprint.
Alternatively light from lJght ~ource 2 ~ay be arranged to 6trike the upper internal ~urface of plate 4 at n angle of incidence greater than the critical angle; in ~hich ca6e light ~trik~ng the surface in ~re~ ~bove ~hich 1~ a rece~s 8 will be totd ly reflected, wh~lst li~ht istri~ing the ~urface in areas at which i8 a ridBe 6 wlll be partially absorbed due to a change i~
the critical angle a6 a result of a modified index of refraction due to the contact of the ridge 6 with the plate 4 ~urface.
Figure 2 ~llu6trates one embodiment of the present invention wherein relatively poor contrast i~ages9 as are obtained by ~uch devices as shown in Figure 1, are at lea~t slleviated.
The o~bodi~ent in Figure 2 compri~e~ ~ light source 16 and collimating lens 18 arranged to produce a broad coll~ated light bea~ 20. Thi8 light 20 is introduced into a l~ght transmltting member 22, which is in the form of a transparent 6ubstrate ~uch as a gla~s or plastics plate, ~la a prism means 24 such as a j 20 glas~ pri~m optically coupled to one ~ajor surface 26 of the light transmitting member 22 by a refractive index coupling mediu~. Alternatlvely, the prism 24 can be formed integrally with the light transmitt~ng member 22.
A second ma~or 6urface 28 of the light tran6mitting member 25 i5 arranged parallel to msjor surface 26. A~ain6t the 6econd major surface 28 i6 held a fiuger 30 from which a fingerprint image i6 to be obtained. It is to be under6tood that the expre6sion "fingerprint" i8 to include all anato~ical attribute6 characteristic of an individual which are suEceptible to the present method 6uch a~ thumb-prints, palm-print6 and foot-print6. The finger is cho6en ~imply a~ lt i8 the mo~t convenient by way of example.
The angle of incidence, q, at ~hich the collimated light 20 6trike~ the upper ~urface Z8 again6t which is placed the finger 30 is arranged to be greater than the critical angle for the medium from which the light tran6mitting member 22 i~
.. . .
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W 0 92/l160# ~ rj ~ ~J 6 : PCT/GB91/022 fon~ed, Aueh as by approp~ately pos~tlon~n~ the light source 16 relative to that area of the major surface 28 desiBnated to recelve the finger.
This mesn6 that light 20 ctriking a point on the ~urface 28 above which ia a reces6 32 of the fi~gerprint ~ill be totally internally reflected, as ~hown schematically by reflected light ray 36, to~ards lo~er surface 26. Light 20 strik$~8 surf~ce 28 in those areas in con~act wlth ~hlch i8 a fineerprlnt ridge 34 will be largely absorbed, scattered and dlffusely reflected, as shown 6chematically by reflected lIght ray 36a, to~ards lower surface 26 but with reduced inten~ty as a result of such processeR.
A direct image producing means 38, in the for~ of a transparent fluorescent pla6tics layer material, is in op~ical cooperation with the lower aurface 26 of ~e~er 22. The dlrect ; image produclng means 38 need not be in direct contsct with ~urface 26, in which case some form of refractive index coupling medium may be required.
Reflected light 36 passes through the light tranfimitting i 20 member 22 via lower surface 26 and impinge6 upon the direct image producing 0eans 38. The reflected light 36 ~8 spatially modified as compared with the incident light 20 due to the ` spatially dependent ab60rption proce~ses ~hich occur ~here the light is internally reflected at the upper 6urface 28 cau6ed by the pressure of ridges 34.
~ The fluore6cent dye within the direct image producing means $ 38 absorb6 the reflected llght 36 incident thereon within a `~ ~pecif~c wavelength ra~ge (governed by the fluoresce~t dye) ant then re-emits light 40 in a characteristic (of the dye) narrow, longer-wavelength rangel a~ determined by the fluorescent dye.
`~ The spatial modulation at this stage is unaffected, that is, the ~`. image of the light is unchanged as between that of the fingerprint on upper surface 28 and that produced by the direct image produclng means 38.
Fluorescence of the dye in the direct image producing ~eane - 38 may be enabled not only by the wavelength characteristics of .
,':`.' , WO 92J1 160X ~ U ~ ~ r~ ~ 3 PCT/GB91/02295 the inc~dent llght, but alao by the intensity of thls light. It will be apparent that those components of reflected light 36 which have undergone total internal reflection at upper 6urface 28 are of greater intensity than those components of reflected . 5 light 36a which have been largely absorbed, scattered and diffusely reflected from upper surf~ce 28. ~ence, by suitable choice of in~tial light 16 inten~ity, and tran~mi~cion coeff~clent~ of the d~rect ~mage producing mesns 387 It i~ pos6ible to arrange for the absorbed,scattered and diffu~ely reflected l~ght 36a to be of insufficient 6ignificant ~ntensity to cause fluorescent within the direct i~age producing means 38.
Thus the image produced will ha~e light areas ~caused b~
fluore6cence) corresponding to those points on the upper surface 28 underlying fingerprint recesses 32; and dark area~ (cau6ed by non-fluorescence) corresponding to those points on the upper surface 28 in contact with fingerprint ridges 34. It will be sppreciated that there will be high contrast between these light and dark areas as compared with prior art devices. Because the lower surface 26 and upper ~urface 28 of the light tran6mittin8 - member 22 are parallel, then lt will be seen that if the direct image producing means 38 is planar, then the plsne of emission of light 40 egre6slng from the direct lmage produc~ng means 38 `~ i8 parsllel to the obje~t plane that 18, the upper surface 28.
This means that there wlll be no spatial distortion between the fingerprint and its fluorescent image, thus obvlating ~ .
'kerbstone' and a~sociated unwanted image distortion effects which would require &nnmorphic correction or compensstion.
Furthermore, because the fluorescence of the ima8e producing means 38 acts in effect as a bac~-projectlon viewing screen or 'secondary' light source, then the image so produced - is a direct image, which means it may by viewed by eye or a video camera 42 or the like. There i6 no optical processing .. required to view the image produced in this way. The si7e ratio of image to subject in the present invention is intrinsically ,.. , 1:1.
. , :: . .. - . . . , , , . .~ :
:~ : .
~:: . ,: ; . . :
.: - ,. . , . . : . . ~. .
W 0 92/l160#~ 3 ~ 8 : PCT/GB91/022 Referring now to Figure 3, wherein similar component6 to that of Figure 2 are like numbered, an alternative embodiment of the present invention i~ illustrated.
In this alternative embodiment, the colli~ated light 20 i6 introduced into the light transmitting member by wsy of a priæm means in the form of a Fresnel priam strip 44. This allows for a more compact device than the previous de8cribed embodiment - employing a prism 24.
Also, Figure 3 details tbe lmage producing means bein8 in the form of a ground glas~ plate 46 or thin layer of non-opaque paint applied to the 6urface 26. Whilst thi~ form of image producing means does not work by fluorescence, the ground glass plate 46 6catters or diffuses the reflected light 36 incident thereon and hence al~o produces a direct image of the fingerprint.
Figure 5 illustrates a further embodiment of the present i invention in which the spatially modulated light 36, 36a i~
permitted to undergo a further total internal reflection at surface 26 before being imaged onto the ground glas6 plate 46.
In this case, the direct image produced is viewed by video camera 42 from lower surface 26 via the light transmitting member 22. Thi6 particular embodiment allow6 for the finger- `
' placement surface to be laterally displaced from the imaging ; screen thereby providing for a compact imaging sy~tem.
It will be appreciated by those 6killed in thi6 art that the present in~ention pro~ides a compact, relatively slim imaging system by suitable choice of the optical component~
described herebefore.
Furthermore, it will be appreciated that the po6sibility ~- 30 exists of providing low-co~t replaceable light transmitting members which may be discarded after a certain amount of use due to the build-up of grease or other deposits on the upper surface thereof Such grease (and dirt) i~ inherent within any skin.
` Also it is possible to overlie the upper surface of the light -' 35 transmitting member with a '~croll' of transparent material or ~ the like such that a fresh ~urface ~ay be presented to each , .
, , ., ~
;~ g~
W 0~)2/116()~ : 9 : PCT/GB91/02295 ., flngerprint, as shown in Figure 4.
It will be apparent to tho~e ~killed in the art that by producing a direct image, the imAge plQne, thst iB the fluore6cent pla6tics layer or ground glass or the like i~
acce6sible. ~ence, any optical calibration which may be required, for example ali~nment of video c~mera 42 ~ay be achieved by simply inserting 60me form of reference grid or "test card" over the direc~ ima~e plane.
It will al80 be appreciated that the present invention ~:
requires no focussin6 or correction elements or the like due to the formation of a direct image. Furthermore, because the invention i~ relatively simple optically, alignment procedure6 :nd a66e=bly c06t6 are nrt extens1ve.
. ~' ' :
.
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-:; -. ,;
Claims (10)
1. A method for forming a direct image of a fingerprint, the method comprising; introducing collimated light into a light transmitting member having first and second parallel major surfaces such that the light interacts with the first major surface thereof, in contact with which is a fingerprint to be imaged, the light then reflecting from the first major surface towards the second major surface, optically coupled with which is a direct image producing means, thereby to form a direct image of the fingerprint.
2. A method according to Claim 1 wherein the collimated light is introduced into the light transmitting member such that the light interacts with the first major surface at an angle greater than the critical angle for the light transmitting member.
3. A method according to Claim 1 wherein the direct image producing means includes fluorescent material thereby to form the direct image by fluorescence.
4. Apparatus for forming a direct image of a fingerprint comprising a light transmitting member having a first major surface for receiving a fingerprint and a second major surface, arranged substantially parallel to the first major surface and in optical cooperation with a direct image producing means, the apparatus arranged for receiving collimated light via the second major surface and reflecting from the first major surface thereby to produce a direct image of a fingerprint.
5. Apparatus according to Claim 4 wherein the direct image producing means comprises a light scattering surface.
6. Apparatus according to Claim 4 wherein the direct image producing means comprises fluorescent material.
7. Apparatus according to Claim 5 wherein the direct image producing means further comprises fluorescent material.
8. Apparatus according to Claim 4 wherein the collimated light is introduced into the light transmitting member via a prism in optical contact with the second major surface.
9. Apparatus according to Claim 4 wherein the light transmitting member comprises a transparent planar member.
10. Apparatus according to Claim 4 wherein the reflection is total internal reflection with the light transmitting member.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB909027718A GB9027718D0 (en) | 1990-12-20 | 1990-12-20 | Fingerprint imaging |
| GB9027718.7 | 1990-12-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2094599A1 true CA2094599A1 (en) | 1992-06-21 |
Family
ID=10687380
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002094599A Abandoned CA2094599A1 (en) | 1990-12-20 | 1991-12-20 | Fingerprint imaging |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0563178A1 (en) |
| JP (1) | JPH06504637A (en) |
| CA (1) | CA2094599A1 (en) |
| GB (1) | GB9027718D0 (en) |
| WO (1) | WO1992011608A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109959981A (en) * | 2017-12-23 | 2019-07-02 | 苏州迈瑞微电子有限公司 | Optical sensor slide glass |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE69407628T2 (en) * | 1993-02-01 | 1998-08-27 | Matsushita Electric Ind Co Ltd | Waveguide image transmission device and fingerprint identification device |
| US6032070A (en) * | 1995-06-07 | 2000-02-29 | University Of Arkansas | Method and apparatus for detecting electro-magnetic reflection from biological tissue |
| US6111977A (en) * | 1997-04-17 | 2000-08-29 | Cross Match Technologies, Inc. | Hand-held fingerprint recognition and transmission device |
| US5900993A (en) * | 1997-05-09 | 1999-05-04 | Cross Check Corporation | Lens systems for use in fingerprint detection |
| US6263090B1 (en) | 1997-05-19 | 2001-07-17 | Cross Match Technologies, Inc. | Code reader fingerprint scanner |
| US6178255B1 (en) | 1998-04-28 | 2001-01-23 | Cross Match Technologies, Inc. | Individualized fingerprint scanner |
| US6272562B1 (en) | 1999-05-28 | 2001-08-07 | Cross Match Technologies, Inc. | Access control unit interface |
| US7308122B2 (en) | 2002-01-17 | 2007-12-11 | Cross Match Technologies, Inc. | Biometric imaging system and method |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2846190A1 (en) * | 1977-10-25 | 1979-05-03 | Michael Schiller | DEVICE FOR PROCESSING INFORMATION ABOUT A FINGERPRINT |
| US4340300A (en) * | 1980-08-11 | 1982-07-20 | Siemens Corporation | Input sensor unit for a fingerprint identification system |
| EP0308162A3 (en) * | 1987-09-15 | 1990-06-06 | Identix Incorporated | Optical system for fingerprint imaging |
| DE68919394T2 (en) * | 1988-09-16 | 1995-03-30 | Fujitsu Ltd | System for detecting a biological object and fingerprint comparison system using this system. |
-
1990
- 1990-12-20 GB GB909027718A patent/GB9027718D0/en active Pending
-
1991
- 1991-12-20 JP JP4502149A patent/JPH06504637A/en active Pending
- 1991-12-20 CA CA002094599A patent/CA2094599A1/en not_active Abandoned
- 1991-12-20 WO PCT/GB1991/002295 patent/WO1992011608A1/en not_active Application Discontinuation
- 1991-12-20 EP EP92901705A patent/EP0563178A1/en not_active Withdrawn
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109959981A (en) * | 2017-12-23 | 2019-07-02 | 苏州迈瑞微电子有限公司 | Optical sensor slide glass |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9027718D0 (en) | 1991-02-13 |
| JPH06504637A (en) | 1994-05-26 |
| WO1992011608A1 (en) | 1992-07-09 |
| EP0563178A1 (en) | 1993-10-06 |
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| Date | Code | Title | Description |
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| FZDE | Discontinued |