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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a fingerprint correlator, and in
particular to an optical fingerprint correlator and the method for
correlating fingerprints by optical means.
The prior art of fingerprint identification and correlation encompasses a
wide variety of techniques for examining and comparing a large database of
fingerprint information containing known fingerprint characteristics with
an unknown fingerprint. Because of the large amounts of data required to
characterize each individual print a substantial computer commitment is
required for handling, storage, and processing of such data. Typically,
fingerprint identification processing of such large amounts of data
requires the use of a mainframe computer. Thus a substantial computer
commitment in terms of hardware, software, operating and support expense,
and processing time relating to the fact that this massive amount of data
typically must be handled by serial operating computers is required. The
quality of correlation possible from the use of prior art fingerprint
correlation techniques is a function of the amount of data used to
characterize each individual print. Thus, the more data per print,
theoretically, the better the overall characterization of each print. In
fact, for legal purposes, a specific number of fingerprint characteristics
must be established in order for the correlation to be deemed valid.
Because of the importance of fingerprint identification, large commitments
of time, money, and resources are typically found to be acceptable when
considered in relation to the alternative manual examination techniques of
the past.
A generalized explanation of the prior art fingerprint identification
process will help to provide the reader with some insight as to the
complexities of the prior art process. First, an unknown fingerprint is
loaded by means of a digitizing scanner, or similar device, into a
computer. Second, the fingerprint information obtained from the digitizer
is divided into pixels. Thus, the fingerprint image would be divided into
a number of pixels, the number of which would relate to the quality of the
result desired. Third, each of the pixels would be assigned a vector
having magnitude and directional information in relation to the
surrounding characteristics of the fingerprint. Thus, typically for each
fingerprint there would be a substantial number of vectors characterizing
its image. Fourth, all of the vectors of the unknown print would then be
compared by the computer to the vectors of the known fingerprint. In the
past, this comparison using existing computers would be performed
serially, and thus can be seen to be a time-consuming process when a large
number of prints would be required to be compared with the single unknown
fingerprint. Fifth, the comparison results determined by the computer
could then be displayed to show the quality of the match between the
unknown and the known fingerprint. In the prior art, techniques have been
used to shorten the process and to make it more efficient by using methods
which would permit pre-sorting fingerprints by certain types of
characteristics, and then zeroing in within the limited group for
comparison with the unknown fingerprint. All such techniques, however, are
found to be very time-consuming and expensive in terms of resource
commitments.
In U.S. Pat. No. 4,790,564, an automatic method and related apparatus for
identifying fingerprints is disclosed. The method and apparatus identified
the fingerprints by means of comparing the minutiae of each fingerprint in
a database of fingerprints with selected ones of pre-computed vector
images of search minutiae in a search print to be identified. The system
determines the probability of a match by comparing the position and angle
of the minutiae being compared between the database file print and the
unknown print.
In U.S. Pat. No. 4,690,554, the invention is a device employing the optical
auto-correlation method for automatically comparing the fingerprint of an
individual with a previously identified exemplar utilizing a pair of
multifaceted mirrors rotating about mutually perpendicular axes to sweep
an image of the fingerprint over the surface of the exemplar in a raster.
A novel optical means is used to compensate for possible angular
misalignment of the fingerprint and the exemplar.
U.S. Pat. No. 4,641,350 describes a fingerprint identification system which
uses a scanner, a memory for storing data representative of fingerprints
received from the scanner, means for comparing newly received data to
reference data, and means for determining the degree of distortion and
misregistration present in the new data relative to the reference data.
The technique disclosed allows the reference array to be stretched and/or
compressed to account for distortion or misregistration in the new data
array. The new data and the reference data are stored in arrays which are
compared by a method which includes dividing the reference array into
subarrays and comparing the elements of each subarray with the elements of
a number of subarrays of the new data array.
It can thus be seen from this brief review of the prior art that in
addition to a large database and a substantial computer commitment for
serial comparisons of "minutiae or substantial arrays of digitized data",
a methodology and apparatus for accomplishing the correlation results
desired by a less tedious and data-intensive technique would be most
productive. Thus, a gross data handling methodology analogous to a
parallel computer process might be considered a more desirable approach.
The present invention, however, provides a methodology of handling the
characterization information about each known and unknown print in such a
way that parallel computing processes are either totally unnecessary or
may be used to advantage to speed up the comparison process even more than
without it. Thus, where under the best of conditions using prior art
technology, perhaps as many as one hundred to a thousand fingerprints per
minute may be compared, the present invention permits a thousand or more
fingerprints to be compared per second.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to speedily and accurately
correlate a large number of known fingerprints with an unknown
fingerprint.
It is yet another object of the present invention to provide the capacity
and methodology for processing a large and legally acceptable quantity and
type of fingerprint characteristic information to permit speedy and
accurate correlation of indicia of known fingerprints in a pre-stored
database with those indicia of an unknown fingerprint.
It is still another object of the present invention to provide a means and
method of gross processing large quantities of fingerprint image
information as an alternative to serial and parallel processing.
It is still another object of the present invention to provide a means and
method of fingerprint correlation using each unknown fingerprint for
autocorrelation calibration of the means for correlation prior to
introducing known fingerprint characterization information for such
correlation.
It is another object of the present invention to provide for known and
unknown fingerprint correlation by optical techniques.
The present invention provides for a database of pre-stored known
fingerprint images for correlation with each unknown fingerprint image
introduced by digital scanner. The unknown fingerprint digitized image is
simultaneously Fourier transformed both optically and digitally. The
digitally transformed image becomes the matched filter which is then
multiplied with the optically transformed image. The multiplied image is
again Fourier transformed and the correlation indicia from this perfect or
autocorrelation match is displayed or stored as user needs dictate. The
known fingerprints, typically stored in a pre-digitized form are then
introduced to the present invention for optical Fourier transform while
the unknown print is simultaneously introduced for digital Fourier
transform and provision of the matched filter. Each known print optically
transformed image is multiplied with the matched filter until the desired
degree of correlation is obtained in relation to the autocorrelation
perfect match. The known prints are introduced serially at a high input
rate, however, the substantial amount of print characterization data is
transformed at one time thus contributing to the overall high throughput
rate of 1000 or more prints per second compared to the lower rates known
in the prior art correlation approaches.
These and other objects, benefits, and advantages of the present invention
will be more readily understood when the following detailed description of
the invention is viewed in light of the accompanying drawing.
BRIEF DESCRIPTION OF THE INVENTION
The accompanying drawing is a block diagram of the functional elements of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
With reference to the Figure, it may be seen that the Optical Fingerprint
Correlator 10, the present invention, is comprised of the unknown
fingerprint loading unit 11 and the known fingerprint loading unit 12. The
unknown fingerprint loading unit 11 is comprised of an image scanner,
having a digital output of an eight (8) bit word for each pixel of the
imaged scanned, and a memory buffer. The known fingerprint loading unit 12
is a digital storage unit such as magnetic or optical memory in a computer
such as a PC (personal computer), minicomputer, or a mainframe.
Pre-scanned image pixel data in the form of eight (8) bit digital words,
typically one eight (8) bit word per pixel for each pixel for each print
is stored in the known print loading unit 12. The unknown print loading
unit 11 and the known print loading unit 12 are connected together through
switch 14.
The unknown fingerprint loading unit 11 is connected through junction 13,
when the switch 14 is open, to the array processor 17 which performs
digital processing including Fourier and Hartley transforms on the digital
array of pixel data representing the scanned image data for each
fingerprint. The digital transform result for each array is communicated
to the spatial light modulator drive 18 which converts the digital
transform data array information it receives from array processor 17 into
analog signals to activate the pixels of the spatial light modulator 32,
an array display device with which it is in communication.
The unknown fingerprint loading unit 11 is connected through junction 13,
when switch 14 is closed, to spatial light modulator drive 16 which is
connected serially to the first spatial light modulator 28. The unknown
fingerprint loading unit 11 provides image information to both spatial
light modulators 28, and 32 when switch 14 is closed for the purpose of
autocorrelation, that is, creating the matched filter of the unknown
fingerprint loading image Fourier transformed both optically and
digitally.
The known fingerprint loading unit 12 is connected through the junction 15
to the spatial light modulator drive 16. The array of digital data
representing the pixels of the scanned image of a known fingerprint
produced by the loading unit 12 is converted to analog signals to recreate
the known fingerprint image at the spatial light modulator 28, an array
display device, with which it communicates.
The optical path of the present invention as depicted in FIG. 1 has the
laser 20 as a source of coherent illumination producing the beam 22 about
the optical axis 24. The lens 26 is centered about the optical axis 24 to
further collimate the light produced by the laser 20. The first spatial
light modulator 28 is centered about the optical axis 24 next beyond the
lens 26 from the laser 20 and in communication with the spatial light
modulator drive 16. The first Fourier transform lens 30 is located next
beyond the first spatial light modulator 28 and is centered about the
optical axis 24. Next in the optical path from the laser 20 after the
first Fourier transform lens 30 is the second spatial light modulator 32
which is centered about the optical axis 24. The second Fourier transform
lens 34 is centered about the optical axis 24 next beyond the second
spatial light modulator 32. The detector unit 36 is the last device in the
optical path from the laser 20. The detector unit 36 is located for
detection centered about the optical axis 24 and beyond the second Fourier
transform lens 34 from the laser 20. A charge coupled device (CCD) camera
having a video output may be used for the detector 36.
The detector 36 is connected to the detection threshold unit 38 which has
preset threshold information in memory for determining minimum level of
detector 36 output it will accept and process. Detector 36 output in
excess of the preset threshold level will be converted from analog to
digital for this purpose and communication to a counter, if desired, and
converted back to analog levels for use by the connected display 40, which
is a video monitor known to those skilled in the art.
In one preferred embodiment of the present invention, the laser 20 is a
Model SP-127-35, 35 milliwatt HeNe visible laser, available from Newport
Corporation, P.O. Box 8020, 18235 Mt. Baldy Circle, Fountain Valley,
Calif. 92728. The first and second spatial light modulators 28 and 32,
respectively, are each Model SM-128 modulators available from Semetex
Corp., 3450 Fujita Street, Torrance, Calif. 90505. The spatial light
modulator drivers 16 and 18 are available from Semetex Corp. (see above),
and are supplied with each of the Model SM-128 modulators. The detector
unit 36 is available from Cohu, 5755 Kearny Villa Road, P.O. Box 85623,
San Diego, Calif. 92123. The detection threshold unit 38 is a model DT2951
frame grabber and is available from Data Translation, 100 Locke Dr.,
Marlboro, MA 01752.
In the preferred embodiment, the unknown fingerprint loading unit 11 which
comprises an optical scanner with memory, the known fingerprint loading
unit 12 comprising magnetic or optical digital storage, and the array
processor 17 comprising the digital Fourier and Hartley transform
capability are implemented as part of the computer (PC, minicomputer, or
mainframe) used to facilitate the high speed operation of the invention.
OPERATION
Referring to the Figure, in order to prepare the Optical Fingerprint
Correlator for operation, a database of known fingerprints is provided and
the unknown fingerprint is introduced to the optical scanner in the
unknown fingerprint loading unit 11. At junction 13 the digital pixel
array data representing the unknown fingerprint is directed in two paths.
The data travels through switch 14 to the first spatial light modulator
drive 16 where the digital pixel data is converted to analog signals used
to turn the pixels of the first spatial light modulator 28 "on" or "off".
The first spatial light modulator 28 is an array display device which
permits the creation of a reconstituted image of the fingerprint being
processed to be communicated to the Fourier transform lens 30. The Fourier
transform image of the image received from the first spatial light
modulator 28 is displayed at the second spatial light modulator 32.
Simultaneous with the communication of the digital data array representing
the fingerprint being processed through the switch 14, the same data is
communicated to the array processor 17. The array processor 17 performs a
digital Fourier transform on the digital data array and sends the
resultant digital transform array, which is the matched filter for the
optically transformed image, to the second spatial light modulator 32
where it is multiplied with the optically Fourier transformed image
arriving from the Fourier transform lens 30. The multiplied image, the
result of the optical Fourier transformed image and the digitally produced
matched filter being brought together at the second spatial light
modulator 32 results from the single fingerprint input being processed for
autocorrelation, as above-described. The multiplied image is communicated
to the second Fourier transform lens 34 and the resultant correlation
image captured by the image detector 36. The correlation peaks, the
indicia of correlation for the particular fingerprint being processed is
passed through the detection threshold unit 38 to set threshold levels for
correlation acceptance and then provided to the display 40 for operator
visualization. The image at the detector 36 represents a match or
correlation since the same fingerprint was simultaneously processed
through the optical Fourier pathway via the first spatial light modulator
28 and the digital Fourier pathway via the array processor 17. This
autocorrelation process, in essence, creates a matched filter for
calibration of the present invention for each unknown fingerprint being
compared or correlated with a known fingerprint being stored as a visual
image, requiring scanning and digitizing in the known fingerprint loading
unit 12, or as pre-scanned and digitized data stored in digital storage
media such as magnetic or optical disk, cards, tape or equivalent employed
in loading unit 12.
Thus, when a matched filter is produced from the autocorrelated image of an
unknown fingerprint and displayed at second spatial light modulator 32,
and with switch 14 then open, known fingerprints stored as visual images
and then scanned and digitized or pre-digitized stored known fingerprint
images can be processed through spatial light modulator drive 16 for
electronic recreation at the first spatial light modulator 28. The
re-created or re-constructed known fingerprint image is then projected to
the first Fourier transform lens 30 resulting in the Fourier transformed
image of the known fingerprint being presented to the image plane within
which the matched filter of the unknown fingerprint resides at the second
spatial light modulator 32. The combined or multiplied images are Fourier
transformed at Fourier transform lens 34 to produce correlation peaks or
indicia indicative of a match or near match, if any, at detector 36. The
detected indicia are then processed by detection threshold unit 38 for
presentation at display 40 or a legally or operationally desirable
alternative device for examining correlation indicia.
It should be obvious to those skilled in the art that the implementation
and mechanization of the fingerprint correlator of the present invention
can be varied considerably to enhance its performance without going beyond
the bounds of the invention as hereafter claimed. As an example, the known
fingerprint loading unit 12 if constituted to contain pre-digitized
fingerprint image data can speed up correlation processing by the
invention considerably greater than if visual images requiring scanning
and digitizing are stored. This is believed to be true even where the
highest speed scanners available to date are used. Also, the detection
threshold unit 38 may be considered as an optional element if the detector
36 is capable of directly driving the display 40.
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