U.S. patent application number 14/309667 was filed with the patent office on 2015-10-15 for smart switching using multispectral imaging.
The applicant listed for this patent is Lumidigm, Inc.. Invention is credited to Robert K. Rowe.
Application Number | 20150294132 14/309667 |
Document ID | / |
Family ID | 44224989 |
Filed Date | 2015-10-15 |
United States Patent
Application |
20150294132 |
Kind Code |
A1 |
Rowe; Robert K. |
October 15, 2015 |
Smart switching using multispectral imaging
Abstract
A multispectral sensor is provided with an illumination source
and a digital imaging system. The illumination source is disposed
to provide light at multiple wavelengths to an object. The digital
imaging system is disposed to receive light scattered from the
object and has a digital array of light detectors and a color
filter array. The color filter array has a multiple distributed
filter elements, each of which is adapted to transmit light of one
of a limited number of specified narrowband wavelength ranges. The
color filter array is disposed to filter the light scattered from
the object prior to encountering the digital array of light
detectors.
Inventors: |
Rowe; Robert K.; (Corrales,
NM) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lumidigm, Inc. |
Albuquerque |
NM |
US |
|
|
Family ID: |
44224989 |
Appl. No.: |
14/309667 |
Filed: |
June 19, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12985161 |
Jan 5, 2011 |
8787630 |
|
|
14309667 |
|
|
|
|
12815196 |
Jun 14, 2010 |
8184873 |
|
|
12985161 |
|
|
|
|
Current U.S.
Class: |
382/124 |
Current CPC
Class: |
G06K 9/00087 20130101;
G06K 9/00899 20130101; G06K 9/00114 20130101; G06K 9/2018 20130101;
G06K 9/00033 20130101 |
International
Class: |
G06K 9/00 20060101
G06K009/00; G06K 9/20 20060101 G06K009/20 |
Goverment Interests
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0003] The Government of the United States may have rights in this
invention.
Claims
1.-17. (canceled)
18. A multispectral smart switch comprising: a switch in electrical
communication with an associated device and having a platen; and an
imaging system disposed to image an object in proximity to the
platen, and to determine, according to the image, whether the
object is a finger, the switch disposed to enable a function of the
associated device only when the object is determined to be a
finger.
19. The smart switch of claim 18, further comprising: an
illumination source disposed to provide light at a plurality of
wavelengths to an object in proximity to the platen, wherein the
imaging system is disposed to image the object by receiving light
scattered from the object.
20. The smart switch of claim 19, wherein the imaging system is
further disposed to determine whether the object is a finger by
analyzing or one or more multispectral qualities of the object from
the image.
21. The smart switch of claim 18, wherein the imaging system is
further disposed to: collect a sequence of image frames; and
analyze the sequence of image frames to detect a motion, wherein
the imaging system is disposed to determine whether the object is a
finger according to the motion.
22. The smart switch of claim 21, wherein the imaging system is
further disposed to determine whether the object is a finger
according to the motion by analyzing the motion relative to that of
a living finger.
23. The smart switch of claim 21, wherein the imaging system is
further disposed to determine whether the object is a finger
according to the motion by analyzing an overall shape of the object
from the sequence of image frames.
24. The smart switch of claim 21, wherein the imaging system is
further disposed to determine whether the object is a finger
according to the motion by analyzing a texture of the object from
the sequence of image frames.
25. The smart switch of claim 21, wherein the imaging system is
further disposed to determine whether the object is a finger
according to the motion by analyzing or one or more spectral
qualities of the object from the sequence of image frames.
26. A method for enabling a function of an associated device using
a multispectral smart switch, the method comprising: imaging an
object in proximity to a platen of a switch in electrical
communication with the associated device determining, according to
the imaging, whether the object is a finger; and enabling the
function of the associated device only when the object is
determined to be a finger.
27. The method of claim 26, further comprising: illuminating the
object with light at a plurality of wavelengths when the object is
in proximity to the platen, wherein the imaging comprises receiving
light scattered from the object.
28. The method of claim 27, wherein determining whether the object
is a finger comprises analyzing or one or more multispectral
qualities of the object derived from the received scattered
light.
29. The method of claim 26, further comprising: collecting a
sequence of image frames; and analyzing the sequence of image
frames to detect a motion, wherein the determining whether the
object is a finger is according to the motion.
30. The method of claim 29, wherein the determining whether the
object is a finger according to the motion comprises analyzing the
motion relative to that of a living finger.
31. The method of claim 29, wherein the determining whether the
object is a finger according to the motion comprises analyzing an
overall shape of the object from the sequence of image frames.
32. The method of claim 29, wherein the determining whether the
object is a finger according to the motion comprises analyzing a
texture of the object from the sequence of image frames.
33. The method of claim 29, wherein the determining whether the
object is a finger according to the motion comprises analyzing or
one or more spectral qualities of the object from the sequence of
image frames.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/818,698, entitled "MULTISPECTRAL BIOMETRIC
SENSOR," filed Apr. 5, 2004 by Robert K. Rowe et al. ("the '698
application"), the entire disclosure of which is incorporated
herein by reference for all purposes. The '698 application is a
nonprovisional of, and claims the benefit of the filing date of
each of the following provisional applications, the entire
disclosure of each of which is incorporated herein by reference for
all purposes: U.S. Prov. Pat. Appl. No. 60/460,247, entitled
"NONINVASIVE ALCOHOL MONITOR," filed Apr. 4, 2003; U.S. Prov. Pat.
Appl. No. 60/483,281, entitled "HYPERSPECTRAL FINGERPRINT READER,"
filed Jun. 27, 2003 by Robert K. Rowe et al.; U.S. Prov. Pat. Appl.
No. 60/504,594, entitled "HYPERSPECTRAL FINGERPRINTING," filed Sep.
18, 2003; and U.S. Prov. Pat. Appl. No. 60/552,662, entitled
"OPTICAL SKIN SENSOR FOR BIOMETRICS," filed Mar. 10, 2004 by Robert
K. Rowe.
[0002] This application is also related to U.S. patent application
Ser. No. 09/874,740, entitled "APPARATUS AND METHOD OF BIOMETRIC
DETERMINATION USING SPECIALIZED OPTICAL SPECTROSCOPY SYSTEM," filed
Jun. 5, 2001, and to U.S. Prov. Pat. Appl. No. 60/576,364, entitled
"MUSTISPECTRAL FINGER RECOGNITION," filed Jun. 1, 2004 by Robert K.
Rowe and Stephen P. Corcoran, the entire disclosures of both of
which are incorporated herein by reference for all purposes.
BACKGROUND OF THE INVENTION
[0004] This application relates generally to biometrics. More
specifically, this application relates to methods and systems for
performing biometric measurements with a multispectral imaging
sensor.
[0005] "Biometrics" refers generally to the statistical analysis of
characteristics of living bodies. One category of biometrics
includes "biometric identification," which commonly operates under
one of two modes to provide automatic identification of people or
to verify purported identities of people. Biometric sensing
technologies measure the physical features or behavioral
characteristics of a person and compare those features to similar
prerecorded measurements to determine whether there is a match.
Physical features that are commonly used for biometric
identification include faces, irises, hand geometry, vein
structure, and fingerprint patterns, which is the most prevalent of
all biometric-identification features. Current methods for
analyzing collected fingerprints include optical, capacitive,
radio-frequency, thermal, ultrasonic, and several other less common
techniques.
[0006] Most of the fingerprint-collection methods rely on measuring
characteristics of the skin at or very near the surface of a
finger. In particular, optical fingerprint readers typically rely
on the presence or absence of a difference in the index of
refraction between the sensor platen and the finger placed on it.
When an air-filled valley of the fingerprint is above a particular
location of the platen, total internal reflectance ("TIR") occurs
in the platen because of the air-platen index difference.
Alternatively, if skin of the proper index of refraction is in
optical contact with the platen, then the TIR at this location is
"frustrated," allowing light to traverse the platen-skin interface.
A map of the differences in TIR across the region where the finger
is touching the platen forms the basis for a conventional optical
fingerprint reading. There are a number of optical arrangements
used to detect this variation of the optical interface in both
bright-field and dark-field optical arrangements. Commonly, a
single, quasimonochromatic beam of light is used to perform this
TIR-based measurement.
[0007] There also exists non-TIR optical fingerprint sensors. In
most cases, these sensors rely on some arrangement of
quasimonochromatic light to illuminate the front, sides, or back of
a fingertip, causing the light to diffuse through the skin. The
fingerprint image is formed due to the differences in light
transmission across the skin-platen boundary for the ridge and
valleys. The difference in optical transmission are due to changes
in the Fresnel reflection characteristics due to the presence or
absence of any intermediate air gap in the valleys, as known to one
of familiarity in the art.
[0008] Optical fingerprint readers are particularly susceptible to
image quality problems due to non-ideal conditions. If the skin is
overly dry, the index match with the platen will be compromised,
resulting in poor image contrast. Similarly, if the finger is very
wet, the valleys may fill with water, causing an optical coupling
to occur all across the fingerprint region and greatly reducing
image contrast. Similar effects may occur if the pressure of the
finger on the platen is too little or too great, the skin or sensor
is dirty, the skin is aged and/or worn, or overly fine features are
present such as may be the case for certain ethnic groups and in
very young children. These effects decrease image quality and
thereby decrease the overall performance of the fingerprint sensor.
In some cases, commercial optical fingerprint readers incorporate a
thin membrane of soft material such as silicone to help mitigate
some of these effects and restore performance. As a soft material,
the membrane is subject to damage, wear, and contamination,
limiting the use of the sensor without maintenance.
[0009] Biometric sensors, particularly fingerprint biometric
sensors, are generally prone to being defeated by various forms of
spoof samples. In the case of fingerprint readers, a variety of
methods are known in the art for presenting readers with a
fingerprint pattern of an authorized user that is embedded in some
kind of inanimate material such as paper, gelatin, epoxy, latex,
and the like. Thus, even if a fingerprint reader can be considered
to reliably determine the presence or absence of a matching
fingerprint pattern, it is also critical to the overall system
security to ensure that the matching pattern is being acquired from
a genuine, living finger, which may be difficult to ascertain with
many common sensors.
[0010] A common approach to making biometric sensors more robust,
more secure, and less error-prone is to combine sources of
biometric signals using an approach sometimes referred to in the
art as using "dual," "combinatoric," "layered," "fused," or
"multifactor biometric sensing. To provide enhanced security in
this way, biometric technologies are combined in such a way that
different technologies measure the same portion of the body at the
same time and are resistant to being defeated by using different
samples or techniques to defeat the different sensors that are
combined. When technologies are combined in a way that they view
the same part of the body they are referred to as being "tightly
coupled."
[0011] There is accordingly a general need in the art for improved
methods and systems for biometric sensing.
BRIEF SUMMARY OF THE INVENTION
[0012] Embodiments of the invention provide a multispectral sensor
that comprises an illumination source and a digital imaging system.
The illumination source is disposed to provide light at a plurality
of wavelengths to an object. The digital imaging system is disposed
to receive light scattered from the object and comprises a digital
array of light detectors and a color filter array. The color filter
array has a plurality of distributed filter elements, each of which
is adapted to transmit light of one of a limited number of
specified narrowband wavelength ranges. The color filter array is
disposed to filter the light scattered from the object prior to
encountering the digital array of light detectors.
[0013] The multispectral sensor may function as a biometric sensor
when the object comprises a skin site of an individual, and may be
configured to detect blanching or blood pooling at the skin site as
part of a spoof detection. In some instances, the filter elements
are distributed according to a Bayer pattern. In some embodiments,
a first polarizer may be disposed to polarize the light provided by
the illumination source, with the digital imaging system further
comprising a second polarizer disposed to polarize the light
scattered from the object. The first and second polarizers may
advantageously be provided in a crossed configuration.
[0014] The multispectral sensor may be incorporated within a
portable electronic device and have such functionality as an
ability to read a bar code, an ability to scan printed matter, an
ability to securely receive data related to functionality changes
of the portable electronic device, and the like. In other
instances, the multispectral sensor may be configured for use as a
smart switch, configured for use as a pointing device, configured
for use a text entry device, configured for measuring an ambient
light condition, and the like. In some embodiments, the
multispectral sensor is integrated with a separate biometric
sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings wherein like
reference labels are used throughout the several drawings to refer
to similar components. In some instances, reference labels include
a numerical portion followed by a latin-letter suffix; reference to
only the numerical portion of reference labels is intended to refer
collectively to all reference labels that have that numerical
portion but different latin-letter suffices.
[0016] FIG. 1 provides a front view of a multispectral biometric
sensor in one embodiment of the invention; and
[0017] FIG. 2 provides a front view of a multispectral biometric
sensor shown in another embodiment.
DETAILED DESCRIPTION OF THE INVENTION
1. Overview
[0018] Embodiments of the invention provide methods and systems
that allow for the collection and processing of biometric
measurements. These biometric measurements may provide strong
assurance of a person's identity, as well as of the authenticity of
the biometric sample being taken, and may be incorporated within a
number of different types of devices, such as cellular telephones,
personal digital assistants, laptop computers, and other portable
electronic devices. In some embodiments, a sensor provides light
that penetrates the surface of an individual's skin, and scatters
within the skin and/or underlying tissue. Skin sites applicable to
multispectral imaging and biometric determination include all
surfaces and all joints of the fingers and thumbs, the fingernails
and nail beds, the palms, the backs of the hands, the wrists and
forearms, the face, the eyes, the ears, and all other external
surfaces of the body. While the discussion below sometimes makes
reference to "fingers," it should be understood that this refers
merely to exemplary embodiments and that other embodiments may use
skin sites at other body parts.
[0019] A portion of the light scattered by the skin and/or
underlying tissue exits the skin and is used to form a
multispectral image of the structure of the tissue at and below the
surface of the skin. As used herein, the term "multispectral" is
intended to be construed broadly as referring to methods and
systems that use multiple wavelengths, and thus includes imaging
systems that are "hyperspectral" or "ultraspectral" as those terms
are understood by those of skill in the art. Because of the
wavelength-dependent properties of the skin, the image formed from
each wavelength of light is usually different from images formed at
other wavelengths. Accordingly, embodiments of the invention
collect images from each of the wavelengths of light in such a way
that characteristic spectral and spatial information may be
extracted by an algorithm applied to the resulting multispectral
image data.
[0020] Embodiments of the invention provide for multispectral
imaging of tissue using a digital imaging system. An illustration
of a simplified arrangement is shown in FIG. 1, which shows one
embodiment for a multispectral biometric sensor 101. The
multispectral sensor 101 comprises one or more sources of light 103
and a digital imaging system 123. The number of illumination
sources may conveniently be selected to achieve certain levels of
illumination, to meet packaging requirements, and to meet other
structural constraints of the multispectral biometric sensor 101.
Illumination passes from the source 103 through illumination optics
that shape the illumination to a desired form, such as in the form
of flood light, light lines, light points, and the like. The
illumination optics 105 are shown for convenience as consisting of
a lens but may more generally include any combination of one or
more lenses, one or more mirrors, and/or other optical elements.
The illumination optics 105 may also comprise a scanner mechanism
(not shown) to scan the illumination light in a specified
one-dimensional or two-dimensional pattern. The light source 103
may comprise a point source, a line source, an area source, or may
comprise a series of such sources in different embodiments.
[0021] After the light passes through the illumination optics 105,
it passes through a platen 117 and illuminates the finger 119 or
other skin site so that reflected light is directed to a digital
imaging system 123. The digital imaging system 123 generally
comprises a digital array 115 and detection optics 113 adapted to
focus the light reflected from the object onto the array. For
example, the detection optics 113 may comprise a lens, a mirror, a
pinhole, combination of such optical elements, or other optical
elements known to those of skill in the art. The digital imaging
system 123 also comprises a color filter array 121, which may in
some instances be incorporated as part of the digital array 115.
The color filter array 121 may comprise a red-green-blue filter
array in the well-known Bayer pattern or in other patterns. In some
instances, the filter elements may function to transmit wavelengths
that differ from the standard red-green-blue wavelengths, may
include additional wavelengths, and/or may be arranged in a pattern
that differs from the Bayer pattern. In instances where such a
color filter array 121 is included, the illumination source(s) 103
may be a white-light or broadband source. Alternatively, the
illumination source(s) 103 may comprise a plurality of narrowband
sources, such as LEDs, with central wavelengths that are within the
pass bands of filter elements comprised by the color filter array
121.
[0022] The sensor layout and components may advantageously be
selected to minimize the direct reflection of the illumination into
the digital imaging system 123. In one embodiment, such direct
reflections are reduced by relatively orienting the illumination
and detection optics such that the amount of directly reflected
light detected is minimized. For instance, optical axes of the
illumination optics 105 and the detection optics 113 may be placed
at angles such that a mirror placed on the platen 117 does not
direct an appreciable amount of illumination light into the
detection subsystem 123. In addition, the optical axes of the
illumination and detection optics may be placed at angles relative
to the platen 117 such that the angular acceptance of both
subsystems is less than the critical angle of the system; such a
configuration avoids appreciable effects due to total internal
reflectance between the platen 117 and the skin site 119.
[0023] The specific characteristics of the optical components
comprised by the multispectral sensor 101 may be implemented to
configure the multispectral sensor 101 for different form factors.
For example, in an embodiment where the multispectral sensor is
implemented in the top of a gear shift as part of a system to
verify the identify of a driver of a vehicle, the light sources 103
and digital array 115 might not fit within the gear-shift handle as
constructed. In such an embodiment, an optical relay system may be
implemented. For example, relay optics that comprise individual
lenses similar to those in a bore scope may be used, or
alternatively optical fibers such as used in orthoscopes may be
used. Still other techniques for implementing an optical relay
system will be evident to those of skill in the art. In this way,
components of the sensor may be located remotely from the sampling
surface.
[0024] The multispectral sensor may take multiple images and
combine them for processing. For example, one image may be made
with one or more illumination wavelengths present and be followed
immediately by an image taken with no illumination turned on. The
difference between these two images allows the effect of
illumination to be separated from background illumination. The
difference image may then be used for further processing according
to other aspects of the invention.
[0025] In some embodiments, the multispectral sensor uses optical
polarizers. One example of such an embodiment is provided in FIG.
2. The basic structure of the sensor 101' is similar to that of
FIG. 1, but polarizers 107 have been added to the illumination
system(s) 121 and a polarizer 111 has been added to the digital
imaging system. The polarizers 107 and 111 may be linear or
circular, or a combination of the two. In the case of linear
polarizers, one useful arrangement is that in which the
illumination light is polarized along a particular axis while the
detected light requires an orthogonal polarization. Such an
arrangement has utility in ensuring that detected light has
undergone multiple scatter events in a medium such as skin. Further
utility is derived from the observation that such an arrangement
greatly reduces the visibility of latent prints left on the platen
117 by previous users, thus providing improved image quality and
reducing the likelihood of spoofing by "reactivating" the latent
prints. The utility of the arrangement also extends to conventional
optical fingerprint readers as well as multispectral imagers. In
particular, dark-field optical fingerprint systems are well-suited
for the addition of linear polarizers in such an arrangement.
Further discussion of a multispectral finger-recognition sensor
that uses such a crossed-polarizer arrangement is described in
copending, commonly assigned U.S. Prov. Pat. Appl. No. 60/576,364,
entitled "MULTISPECTRAL FINGER RECOGNITION," filed Jun. 1, 2004 by
Robert K. Rowe and Stephen P. Corcoran, the entire disclosure of
which is incorporated herein by reference for all purposes.
2. Applications
[0026] In a number of specific embodiments, A multispectral imaging
sensor may be incorporated in a cellular telephone, a personal
digital assistant, a laptop computer, or other portable electronic
device. Such a multispectral sensor may be configured to collect
multispectral biometric data on a finger. The sensor may require
that a person touch the sensor, or may be able to collect the
necessary multispectral data in a noncontact fashion with
appropriate images being collected while the skin is located at a
distance from the sensor.
[0027] In some embodiments, the multispectral imaging sensor
incorporated in a portable electronic device may contain an optical
system to enable adjustable focus. The mechanism for adjusting the
may include one or more lenses that may be moved into various
positions. The focusing mechanism itself may be a conventional zoom
arrangement. Alternatively, the mechanism for focusing may use a
liquid lens based on the known phenomenon of electro-wetting.
[0028] In a system configuration in which the portable electronic
device has been designed to accommodate a "close-up" or macro image
of the finger for biometric sensing, the same optical system may be
used to read an optical code such as a barcode. Such a barcode
reading could, for example, initiate a service in which product
information for a product corresponding to the UPC barcode is
downloaded to the portable device to provide the consumer with
comparative pricing and performance data. Similar barcode scans may
be used in other embodiments for promotional games or various
gaming activities. The conjunction of a barcode scan taken in close
temporal proximity to a biometric scan could provide for an audit
trail for legal matters, including financial documents and
transactions, forensic chain-of-evidence scenarios, and a variety
of logical and/or physical security applications.
[0029] An imaging system on a portable electronic device that is
configured to collect multispectral biometric data may also be used
to scan in text, graphics, or other printed matter. In the case of
text, the scanned data may be converted to an interpretable form
using known optical-character-recognition ("OCR") techniques. Such
text recognition may then be used to provide input of
text-translation services, copying services, and other such
services that may be aided by a rapid and convenient character
input.
[0030] An imaging system on a portable electronic device may also
be used as an optical input device to provide a mechanism for
securely inputting data into the device for functions such as
reprogramming, security overrides, and secure digital
communications. The illumination components of the imaging system
may be used as optical output devices in the reverse direction from
the detector elements. The use of multiple, filtered wavelengths
can provide proved for multiple high-bandwidth channels for rapid
and/or robust optical communication.
[0031] The multispectral sensor may also be used as a smart switch
to turn on or enable an associated device, system, or service. In
such a capacity, the multispectral sensor may be set to a
video-streaming mode to collect several frames per second. Each
frame may then be analyzed to detect motion and, if motion is
detected, perform image processing steps to confirm that the motion
is due to a finger by analyzing the overall shape, the texture,
and/or the spectral qualities relative to a living finger.
[0032] The multispectral sensor may be used as a pointing device
with similar functionality as a touchpad commonly used on a laptop
PC. The multispectral sensor can be used in this fashion by
monitoring the motion of the finger over the sensing area. Sliding
the finger in a linear motion to the left can indicate a leftward
motion to the PC (or cell phone, PDA, or other device), with
similar effects for motions to the right, up, down, diagonal, or
other directions. The cursor of the PC (or cell phone, PDA, or
other device) may then be made to move in the indicated direction,
or other appropriate action may be taken. In a similar fashion, the
surface of the sensor may be tapped in different regions to
simulate a click or double-click of a conventional PC mouse. Other
motions, such as circles, X's, and the like, may be used to
indicate other specific actions. In the case of touching or tapping
the sensor, the degree of pressure may be estimated by evaluating
the degree of blanching occurring in the finger. In this manner,
different actions may be taken in response to a soft pressure being
sensed relative to a hard pressure.
[0033] The spectral qualities of the finger in motion may be
assessed to ensure that the detected motion is from that of a
finger rather than some spurious object. In this way, false motions
can be avoided.
[0034] The sensor surface may also be used as a simple text entry
device. In a similar fashion as in the case of a pointing device,
the user may make motions with the fingertip that describe single
letters or number, which are then accumulated by the portable
electronic device.
[0035] A particular motion of the finger may be used to increase
the security of the sensing system. In such a configuration, the
spectral and spatial qualities of the finger are confirmed to match
those that are on record while the particular finger motion that is
made is assessed to ensure it is similar to the motion on record.
In this way, both the finger qualities and the motion need to match
in order to determine an overall match.
[0036] The multispectral sensor may be used to measure the ambient
light condition. In order to do so, an image is taken without any
illumination light turned on at a time when a finger is not
covering the sensor surface. The amount of ambient light may be
determined from the image. Further details about ambient lighting
may be derived in the case where the imager uses a color filter
array or a similar mechanism to assess spectral characteristics of
the light. The measure levels of ambient light may then be used by
the associated device to set levels for display brightness,
backlighting, etc. Such settings are particularly useful in
ensuring the usability of portable electronic devices while
conserving battery usage.
3. Combinations of Multispectral Sensing with Other Biometric
Sensors
[0037] A small and rugged embodiment of a multispectral sensor may
be constructed from solid-state components such as silicon digital
imaging arrays and light-emitting diodes. Such a sensor may be
integrated into a conventional fingerprint sensor to provide a
second biometric reading when a fingerprint is taken. The
conventional fingerprint sensor may be an optical fingerprint
sensor. The multispectral sensor may use one or more illumination
wavelengths to sense optical characteristics of the skin, including
the presence, degree, and/or distribution of blood in the finger or
other body part. The illumination wavelength(s) may include one or
more wavelengths shorter than approximately 600 nm, where blood is
known to become highly optically absorbing and thus discernible
from other tissue components.
[0038] The images taken by the multispectral sensor prior to the
finger touching the sensor may be used in whole or in part to
perform a biometric assessment of the person's identity. In the
case of a fingerprint, the individual ridge lines may be identified
and tracked through a series of images to quantify the degree and
type of distortion that such ridge images undergo when pressure is
applied to the sensor by the finger.
[0039] The fingerprint pattern observed by the multispectral imager
using one or more illumination wavelengths may be combined with the
TIR pattern to provide a combinatoric biometric. The multispectral
image may contain information on the external friction ridge
pattern, the internal friction ridge pattern, the composition and
position of other subsurface structures, the spectral qualities of
the finger, the size and shape of the finger, and other features
that are somewhat distinct from person to person. In this way, one
or more multispectral features may be combined with the optical
fingerprint data to provided additional biometric information.
[0040] In some cases, the multispectral imaging data may be
processed to improve the quality of the TIR fingerprint. In
particular, there may be a linear or nonlinear numerical
relationship established on parts of the image where both the
multispectral image data and TIR data are well defined. These parts
are then used to establish a mathematical model such as with
Principal Component Regression, Partial Least Squares, Neural
Networks, or other methods to one familiar in the art. The parts of
the TIR image that are missing due to poor contact, etc. can thus
be estimated from the model so established. In another embodiment,
the entire images may be used, but the numerical model built using
robust statistics in which the relationship is relatively
unaffected by missing or degraded portions of the TIR image.
Alternatively, numerical models may be established through the
examination of previously collected TIR/multispectral image sets
and then applied to new data.
4. Spoof Detection
[0041] The multispectral sensor may be used to make a determination
about the authenticity of the sample and thereby detect attempts to
spoof the optical fingerprint sensor. The multispectral sensor may
be able to make a static spectral reading of the sample either when
it touches the sensor surface or at a remote distance to ensure
that the spectral qualities match those of a living finger.
[0042] The multispectral sensor may also use one or more
illumination wavelengths to illuminate the finger as it moves to
touch the sensor surface. During this interval of time, blanching
of the skin may be observed in the vicinity of the sensor as
pressure is applied by the finger. As well, areas of the skin may
show a distinct pooling of blood, especially those regions at the
perimeter of the area of contact between the finger and sensor.
This blanching and/or pooling of the skin provides an identifiable
set of changes to the corresponding images. In particular,
wavelengths less than approximately 600 nm, which are highly
absorbed by the blood, are seen to get brighter in the region of
blanching and darker in areas of blood pooling. Wavelengths longer
than approximately 600 nm are seen to change much less during
blanching and/or pooling. The presence, magnitude, and/or relative
amounts of spectral changes that occur while the finger touches the
fingerprint sensor can be used as an additional means of
discriminating between genuine measurements and attempts to spoof
the sensor.
[0043] In the case where the multispectral sensor is combined with
an optical TIR fingerprint reader, the pattern detected by the
multispectral sensor using one or more illumination wavelengths may
be compared with the pattern detected by the fingerprint sensor and
consistency confirmed. In this way, the internal fingerprint data
due to blood and other subsurface structures is used to confirm the
image of the external fingerprint that the conventional fingerprint
sensor collects. If there is a discrepancy between the two
patterns, an attempt to spoof the fingerprint sensor using a thin,
transparent film placed on the finger may be indicated. Appropriate
action may be taken in response to this discrepancy to ensure that
such a spoof attempt is not being perpetrated.
[0044] Other factors that can be monitored to discriminate between
genuine finger and attempts to spoof the detector using an
artificial or altered sample of some kind include monitoring the
image taken with 1 or more wavelengths over time. During the
specified time interval, changes such as those due to pulse can be
measured and used to confirm a genuine finger. As well, changes in
the image due to sweating at the ridge pores can be observed and
used for spoof detection.
[0045] Thus, having described several embodiments, it will be
recognized by those of skill in the art that various modifications,
alternative constructions, and equivalents may be used without
departing from the spirit of the invention. Accordingly, the above
description should not be taken as limiting the scope of the
invention, which is defined in the following claims.
* * * * *