CA2055539A1 - Method and apparatus for fingerprint image processing - Google Patents

Abstract

Abstract A finger drying component for use with a finger print image processing apparatus is disclosed. The drying component removes moisture from the finger so that an unsmudged finger print can be imaged. A
preferred embodiment involves the use of a forced air dryer to conduct a stream of air across the optical imaging surface.

Description

METHOD AND APPARATUS FOR FINGERPRINT ~ ~j 3 ~ '~
IMAGE PROCESSING

5Backqround of -the Inventlon This invention relates generally to a fingerprint image processing apparatus, and more particularly ~o an apparatus and a method for removing moisture from contact surfaces of such apparatu~, or from the finger of a subject to be imaged, or from both.
Originall~, fingerprinting was done by inking a suspect's finger and applying the inked finger to paper.
As can be readily understood, fingerprint information in this form was difficult to use. Making a fingerprint match was an extremely time-consuming task. Digital technology significantly advanced the art of fingerprinting. Inked images could be scanned, the image digitalized and recorded in a manner that could later be ~earched in a reasonably expeditious manner by computer. Problems arose, however, due to the quality of inked images. Over- and under-inking resulted in blurred or vague images, thus rendering the digitalized information useless. Further, the process of scanning an inked image was relatively time consuming.
These and other problems led to "live scanning." According to live scanning techniques, the fingerprint of a suspect is scanned directly from the suspect~s finger, as opposed to being scanned from an inked image of the print. More specifically, live scans are those procedures which capture fingerprint ridge detail in a manner which allows for the immediate processing of the fingerprint image with a computer.
Orisinal work in the field dates back to original patents filed in 196~ concerning techniques used to capture high contrast images of fingerprint for photographic or digital capture of fingerprints.
Since their introduction, live scans have become an important tool ~or law-enforcement. The live scan has the potential co overcome inherent weaknesses

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in the Lnk capture of fingerprints. In parti.cular, live scans are advantageous becaus~ they reduce over or under inking; reduce smudging or smearing; provide immediate transmission of fingerprint images; and allow for image enhancement if necessary.
These chaxacteristics provide law-enforcement with the ability to improve the quality of the fingerprint data base, thereby improving the likelihood that identifications can be made either from latent fingerprints or from identity verification checks.
Fingerprint image processing systems have been disclosed in the literature and in patents. An example of one type of image processing system is shown in United States Patent No. 4,322,163 to Schiller.
Schiller '163 discloses an optical assembly for fingerprint image generation, which includes a reflective layer incorporated between a resilient layer and a flat glass base or platen. The force transmitted by a finger pressed against the back surface of this platen will cause the resilient layer to deform and provide a scannable image. Diyital Biometrics, Inc. has recently published brochures describing an apparatus for obtaining a fingerprint image through a hard prism.
Contact by a finger with a planar surface of the prism results in a high contrast image reflected onto sensor means for processing of the fingerprint image.
Generally, as can be understood from the discussion above, known fingerprint imaging apparatus and methods involve placement of one or more of the fingers of a human subject onto a surface which is then scanned to provide an image of the fingerprint. As can be readily understood, the process of being arrested can be particularly stressful~ and it has been found tha-t individuals often perspire while being fingerprinted.
It has also been found that the presence of such perspiration, sweat or other moisture on the subject's finger or fingers, or on the contact surface, during

3 3 image processing results in an imag~ of reduced clarity.
The image may, in fact, be so dis~orted as to be of little or no use in identificcltion. More specifically, perspiration affects the clielectric surface properties of the finger. The effect is an optical, or electromagnetic phenomenon which distorts the fingerprint image.
Accordingly, it is an object of the present invention to provide a method and an apparat-l~ suitahle for removing such perspiration or othar moisture from the finger or fingers of the subject, and/or from the contact surface itself.

Summary of the Inventio_ This disclosure descrihes a fingerprint image processing apparatus, as well as a method for preparing a finger for fingerprint image processing.
The apparatus disclosed herein is a means for imaging having a contact surface that can receive one or more fingers thereon. As used herein, "means for imaging" refers to any apparatus, device or system useful for generation of a scanned fingerprint. The present means for imaging will have one or more surfaces, hereinafter referred to as "contact surfaces,"
upon which a human subject will place his or her finger or fingers for the purpose of scanning the image $hereof. Typically, such contact surfaces will be formed from clear, non-absorbent materials such as glass, plastic, or a combination thereof. Moisture can accumulate on these non-absorben~ contact surfaces, from the subject's finger, -from the air, or elsewhere.
To alleviate this problem, the fingerprint image processing apparatus of the present invention also incorporates a drying arrangement. The drying arrangement is intended for the removal of the accumulated moisture sucn as perspiration or sweat from the contact surface, or from the finger itself, or from `
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both the contact surface and the firlger. In order -to be ~ffective at removing moisture from the contact surface, the dxying arrangement will be positioned in proximity therewith.
Although it is contemplated that any suitable means known to those of ordinary skill in the art for removing moisture from surfaces may be used ~s a drying arrangement of the present apparatus, a preferred drying arrangement includes a device or mechanism for generating a flow of air and structure or a mechanism for directing that air across the contact surface.
Preferably, the structure for directing air includes a hollow tube through which air passes, and having at least one aperture, which may be a hole, slit or other opening, through which a flow of the air can be exhausted. The aperture is preferably positioned so as to exhaust the flow of alr in the direction of the contact surface.
In a preferred embodiment of the apparatus of the present invention, the volumetric f low rate of the flow of air through the tube is most preferably about 25 to 30 cubic feet per minute. In specific embodiments of the present apparatus wherein the contact surface has an area of about 6 to 10 square inches, the aperture in the tube will also preferably be a slit of a square or rectangular shape, having dimensions of about 1 to 4 inches in width and about 1/4 to 1/2 inches in height.
The drying arrangement of the present apparatus is also capable of removing moisture from the finger, either in addition to removing moisture from the contact surface, or alternatively, when the finger held in proximity with the contact surface.
Other examples of a drying means useful in the present apparatus include, for example, means well known in the art which employ a desiccant, an evaporative liquid, or the like for moisture removal. Useful desiccants lnclude, for example, silicas, magnesium or .~

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sodium sulfa-te alone or in mixt-lre with inert carriers as well as diatomaceous earth and clays. Useful evapora-tive liquids include low molecular weighk alcohols, ketones, and ethers and the like which can leach or extract water or water based moisture from a surface and which rapidly evaporate at typical room temperature. In a preferred c~mbodiment, these alterna-tive drying means can be placed in proximity with the contack surface by locating ~n open container holdiny the drying means adjacent the contact surface.
The finger is wiped across the dryi.ng means and preferably in a continuous ~novement is transferred to the contact surface.
The present inven~ion further provides a me-thod for preparing a Einger for optical fingerprint image processing. The me-thod includes the steps of providing a fingerprint image processing apparatus as described hereinabove, and exhausting a flow of air from the drying means in the direction of the contact surface, so as to evaporate moisture therefrom, or from a finger held in proximity with the contact surface, or from both.
The moisture ~nich is removable by the present method is typically human persp~ration, sweat, water or other evaporable li~uid. Loose soil or other particulate matter present on the finger may incidentally be removed ~y che force of the flow of air.
Typically, when the flow rata of the air stream is about 25 to 30 cubic feet per minute, a period of time of less th~n about one or twc, seconds is sufficien~ for removing all or substantially all moisture from the finger prior to placeme~t of the fi;lger on the contact surface~

Brief Descri~tion of the Drawinqs Figure l is -an elevated perspective view of an apparatus constructed ~ccording to the preferred embodiment of the prese~ in~ention;

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Figure 2 is an elevated perspective view of the apparatus illustrated in Figure 1, with a portion of the apparatus displaced from its typical in-use position, and with a portion of the apparatus shown in cutaway;
Figure 3 is a partial., enlarged, eleva~ed perspective view of the apparatus of Figwre 1;
Figure 4, is a partial, enlarged/ perspec-tive ~iew of an alternate embodiment of a portion of the apparatus illustrated in Figure l;
Figure 5 is an explocled, assembly view of a portion of the portion of the apparatus lllustrated in Figure 4.

Detailed Description of the Preferred Embodiments Referring now to the drawings, wherein like reference numerals designate corresponding elements throughout the views and particularly referring to Figure 1, a fingerprint image processing system 8 is shown. The fingerprint image processing system 8 includes a device for imaging 9 that may be any one of a number of known imaging apparatus. For instance, the apparatus may be an optical image processing system, such as that described by Digital Biometrics, Inc. as Model No. 1133R. The image processing apparatus 10 has a housing 11 which generally encloses the scanning and image processing equipment. The housing 11 has a front portion 12 on which is mounted at least one image-projecting, or "contact", surface upon which a person being fingerprinted places a finger or fingers.
The embodiment illustrated in Figure l includes two such surfaces 20 and 21 which are sized for placement of all fingers and one finger respectively. The remainder of the Detailed Description focuses largely on surface 20, but it is to be understood that surface 21 is substantial3.y similar to surface 20, but for minor differences which will be noted.

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r~ f l The surface 20 is prefera~ly one slde of ~ hard plastic prism. An image of the fingerprin-t of the finger resting on -the surface 20 is projected through the prism 22 and is scanned and recorded by the internal image processing system (not shown) in a known mainner.
Contact surface 20 is preferably mounted in housing 11 by a frame 25, illustrated in Figures 1 and 2. That is, prism 22 is preferably fixed, such as by gluing or bolting, in frama 25, such that surface 20 is coplanar with, or does not protrude from, frame 25. Frame 25 i5 fixed to the housing 11 for instance by screws 28 through the frame 25 which extend into the housing 11.
Contact surface 20 is sized to accommoda-te a thumb or a single digit. In the embodiment illustrated in Figure 1, the surface 20 is rectangular and i9 between about 2 inches x 3 inches and 4 inches x 4 inches.
Surface 21 is somewhat larger than surface 20 and is sized to accommodate several fingers at one time.
Surface 21 is between about 3 inches x 3 inches and 5 inches x 5 inches.
Image processing system 10 further includes a mechanism or arrangement 40 for drying the image-projecting surface 20 and/or for drying the fingerts) of a person being fingerprinted. The drying arrangement 40 is preferably located is close proximity to the surface so tha-t the person being fingerprinted will ha;ve his or her finger dried as it is lowered onto the surface. Further, the drying arrangement is constructed and arranged to dry the finger and the contact surface 20 as the image of the fingexprint is scanned.
In the most preferred embodiments indicated by Figures 1-3, drying arrangement 40 includes structure 45 for generating air flow and structure 47 for directing that air flow across the contact surface 20. In the embodiment illustrated in Figures 1-3, the structure 45 for generating air flow is a fan 55 or a blower, visible ' ~ 3~ 9 in Figure 2. For convenience, the fan 55 is located in the bottom portion o~ housing 11. The fan 55 generates air flow and has an outlet 57 that is in fluid communication with the structure 47 for directing air flow across the image-projecting surface 20.
In the most preferred embodiment, illustrated in Figures 1-3, the structure 47 for directiny air flow from the fan to and across the image-project1ng surface includes an inlet 58 and an outlet 59. The outlet 59 is visible in Figures 1 ancl 3. The inlet 58 is attached to and in ~luid communication with the fan outlet 57. ~he air outlet 59 is located in relatively close proximity to the surface 20.
More specifically, the struc-ture 47 for directing air flow includes a flexible hose 60 and a conduit 62.
The hose 60, illustrated in Figure 2, has first and second opposite ends 65 and 66, respectively. First end 65 engages and is attached to the ~an outlet 57. The conduit 62 has first and second opposite ends 70 and 71, respectively. The second end 66 of hose 60 is attached to and in fluid communication with the first end 70 of conduit 62. Conduit 62 includes openings or apertures - 80 through which the conduit 62 is in fluid communication with the atmosphere. In this manner, the air flow generated by fan 55 flows from fan outlet 57, is directed through hose 60 and conduit 62 and then i5 exhausted through apertures 80.
In the preferred embodiment, as illustrated in Figure 2, hose 60 extends through an aperture or opening 75 of the housing 11. Conduit 62 is preferably elongated and substantially rigid. S~ructure is provided for attaching the second end 71 of conduit 62 ; to the housing 11 of the optical imaging device 9. Any conventional attachment means may be used to attach second end 71 of conduit 62 to the housing 15. In the embodiment shown, the attachment mechanism is a snap, with one portion of the snap (not shown) attached to the ~3 7,,? ( conduit second end 71 ancl the other portion 81 of the snap attached to the housing 17. Other attachment mechanisms including velcro or the like may be used as well. Further, the housing 11 may include structure for S supporting the conduit 62 removably or permanently thereon.
~ s illustrated in Fiqure 1, in typical use, the conduit 62 is supported at both ends and is secured to the housing 17, such that the conduit 62 extends substantially horizontally across the front of the housing 17. In the embodiment illustrated in Figures 1 and 2, the conduit 62 has an outwardly pyramid-type shape. That is, it is triangular in transverse cross-section. It is to be understood that the conduit 62 may be of any suitable shape.
As can be understood with reference to Figure 1, apertures or slots 80 in conduit 62 are positioned in close proximity to image-projecting surface 20. Because the embodiment in Figure 1 includes two contact surfaces 20 and 21, two respective slots 80a and 80b are provided. That is, a first slot 80a is positioned adjacent image-projecting surface 20; aperture or slot 80b is positioned adjacent image-projecting surface 21.
Each aperture or slot 80 is sized, shaped, and oriented to direct air flow toward and across its associated surface 20. This is illustrated in Figure 3. Arrows 90 indicate the direction of air flow across tha surface 20 in the most preferred manner. In the most preferred embodiment, the slot 80 is rectangular-shaped and is between about 1 and 4 inches in width, with a height of between about 1/4 to 1/2 inches. For a surface 20 having a width of bet~7een about 1.5 to 2 inches, slot 80 preferably has a width of between about 1.5 to 1.7 inches, and is spaced about 1 or 1.1 inches from the nearest edge of the surface 20. Most preferably, for a surface 20 having a widtll of 1.9 inches, slot 80 has a 1 o 2 ~ 5 3~
width of about 1.625 inche~, and i~ spaced about 1.05 inches from the nearest edge of the surface 20.
Further, in the most preferred embodiment, the air flow from the fan, and the si~e of apertures or slots 80 are such that the volumetric flow rate from each slot is approximately 27 cubic feet per minute. It has been found that this volumetric flow rate 15 adequate to dry a suspect's finger in less than about three seconds and preferably within one to two seconds when placed in the path of the air flow. Further, the diameters of hose 60 and conduit 62 are preferably such as to minimize pxessure drop between khe fan and the slots 80.
A second embodiment of air flow directing lS structure 110 is illustrated in Figures 4 and 5.
Contact surface 115 is mounted to the housing 116 of the image processing system by a mounting frame 120 in a manner substantially similar to the mounting of surface 20 in housing 11 described above. In this alternate embodiment, contact surface 115 is partially surrounded by a conduit frame 125. The conduit frame 120 includes three segments 140, 141 and 142. The segments 140, 141 and 142 are generally elongate members joined to one another at their ends, at right angles, as illustrated 25 in Figure 4. The segments 140-142 are of appropriate length to abut one end 150 and portions of adjacent sides 155 and 156 of the mounting frame 120.
Referring now to Figure 5, it will be understood that the segments 140-142 are in fluid 30 communication. That is, each of the segments 140-142 includes a passage 160, 161 and 162, respectively, therethrough, and the passages 160, 161 and 162 are in fluid communication with on another. The conduit frame 125 is connected to a fan (not shown) through a tube As illustrated, in Figure 5, tube 165 is attached to segment 141 with a hose barb union 170. An O-ring 175 is positioned between segments 140 and 14l to ..
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enhance a fluid-tight seal between passages 160 and 161.
Similarly, an O-ring tnot shown) is disposed between segments 141 and 142 to enhance a fluid~tight seal between passages ]61 and 162. Segment 160 is secured to segment 161 with, for instance, a screw 1~0 passing through a portion of segment 141 and into a portion of segment 140. In the preferred embodiment, the screw 180 does not interfere with the air passages 160 and 161.
Segment 142 is secured to segment 141 in a similar manner.
As illustrated in Fi.gures 4 and 5, segment 142 includes a plurality of apertures 185 iJI fluid communication with passage 162. ~he aper~ures 185 are positioned on the side oflsegment 142 adjacent to the contact surface 115. Similarly, segment 140 includes apertures (not shown) in fluid communication with passage 160. Apertures 185 and the apertures in segment 140 are constructed and arranged to direct air toward the contact surface llS. Most preferably, the aix is directed in an angled îashion as illustrated by the arrows 190 in Figure 4.
Most preferably, the number of apertures 185, the cross-sectional area of apertures 185, and the volumetric flow rate produced by the fan cooperate such that the combined flow rate from the apertures is between about 25 and 35 cubic feet per minute.
In the embodiment illustrated in Figures 4 and 5, apertures 185 are generally circular in cross-section. It is to be understood, however, that other shapes and constructions of apertures are contemplated. For instance, rectangular slots may he employed in the segmen-ts 140 and 142. Additionally, aper~ures, holes, or slots, may be included on segment 141 directed toward the image-projecting surface 115.
This invention further includes a method of preparing a finger for optical fingerprint image processing. The preferred method includes drying the ' !J

finger or fingers to be scanned immediately prior to scanning the finger. Additionally or alternatively, the method includes drying the firlger during scanni.ng.
Additionally or alternatively, the method includes drying the contact surf,ace pri.or to and during scanniny.
More specifically, the method includes exhausting a flow of air across the surface upon which the finger of the person beinsl fingerprinted will rest while being scanned. As the finyer is lowered onto the contact surface, the air flow will dry the finger.
Further~ the air flow may continue to dry the ~inger as the finyer rests on the surface during scanning. Still further, the air flow may dry the con~ack surface prior to and/or during scanning.
The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope of the invention.

Claims (12)

WE CLAIM:

1. A fingerprint image processing apparatus comprising:
(a) a means for imaging having a contact surface adapted to receive a finger thereon; and (b) a drying means in proximity with said contact surface, aid drying means adapted for removing moisture from said contact surface, or from a finger which is in proximity with said contact surface, or from both of said contact surface and said finger.

2. An apparatus of claim 1 wherein said drying means comprises a means for supplying air flow across said contact surface.

3. An apparatus of claim 2 wherein said means for supplying air flow comprises a tube having at least one aperture positioned so as to exhaust a flow of air therefrom in the direction of said contact surface.

4. An apparatus of claim 3 wherein a volumetric flow rate of said flow of air is about 25-30 cubic feet per minute.

5. An apparatus of claim 3 wherein a surface area of said contact surface is about 6-16 square inches.

6. An apparatus of claim 3 wherein said at least one aperture is a slit which is rectangular in shape.

7. An apparatus of claim 6 wherein said slit has a length of about 1-4 inches and a height of about 1/2-1/4 inches.

8. An apparatus of claim 1 wherein said moisture comprises human perspiration.

9. A method for preparing a finger for fingerprint image processing, comprising the steps of:
(a) providing a fingerprint image processing apparatus comprising a means for imaging having a contact surface adapted to receive a finger thereon, and a drying means in proximity with said contact surface, said drying means adapted for removing moisture from said contact surface, or from a finger which is in proximity with said contact surface, or from both of said contact surface and said finger; and (b) exhausting a flow of air from said drying means so as to evaporate moisture from said contact surface, or from said finger, or from both of said contact surface and said finger, prior to imaging a fingerprint of said finger.

10. The method of claim 9, wherein said moisture comprises human perspiration.

11. The method of claim 9, wherein a volumetric flow rate of said flow of air is about 25-30 cubic feet per minute.

12. The method of claim 11, wherein said evaporation is accomplished during a period of time which is less than about three seconds.