EP2041697A1 - Capteurs biométriques spectraux - Google Patents

Capteurs biométriques spectraux

Info

Publication number
EP2041697A1
EP2041697A1 EP07873944A EP07873944A EP2041697A1 EP 2041697 A1 EP2041697 A1 EP 2041697A1 EP 07873944 A EP07873944 A EP 07873944A EP 07873944 A EP07873944 A EP 07873944A EP 2041697 A1 EP2041697 A1 EP 2041697A1
Authority
EP
European Patent Office
Prior art keywords
skin site
light
biometric
purported skin
image
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.)
Ceased
Application number
EP07873944A
Other languages
German (de)
English (en)
Other versions
EP2041697A4 (fr
Inventor
Robert K. Rowe
Stephen P. Corcoran
Kristin A. Nixon
Ryan Martin
Todd Doucet
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
HID Global Corp
Original Assignee
Lumidigm Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from US11/458,607 external-priority patent/US7751594B2/en
Priority claimed from US11/458,619 external-priority patent/US7545963B2/en
Application filed by Lumidigm Inc filed Critical Lumidigm Inc
Publication of EP2041697A1 publication Critical patent/EP2041697A1/fr
Publication of EP2041697A4 publication Critical patent/EP2041697A4/fr
Ceased legal-status Critical Current

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
    • G06V40/1347—Preprocessing; Feature extraction
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F18/00—Pattern recognition
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • 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
    • G06V40/1382—Detecting the live character of the finger, i.e. distinguishing from a fake or cadaver finger
    • G06V40/1394—Detecting the live character of the finger, i.e. distinguishing from a fake or cadaver finger using acquisition arrangements
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/117—Identification of persons
    • A61B5/1171—Identification of persons based on the shapes or appearances of their bodies or parts thereof
    • A61B5/1172—Identification of persons based on the shapes or appearances of their bodies or parts thereof using fingerprinting
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7235—Details of waveform analysis
    • A61B5/7253—Details of waveform analysis characterised by using transforms
    • A61B5/726—Details of waveform analysis characterised by using transforms using Wavelet transforms
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7235—Details of waveform analysis
    • A61B5/7264—Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems

Definitions

  • This application relates generally to biometrics. More specifically, this application relates to methods and systems for performing biometric measurements that use spectral information.
  • 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.
  • TIR total internal reflectance
  • 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 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.
  • Optical fingerprint readers such as those based on TIR, as well as other modalities such as capacitance, RF, and others, typically produce images that are affected to some degree by the nonideal imaging conditions present during acquisition. An analysis of the textural characteristics of the resulting images is thus affected by the sampling conditions, which may limit or obscure the ability to observe the textural characteristics of the person's skin. The consequence of this is that texture is of limited utility in such sensing modalities.
  • Biometric sensors are generally prone to being defeated by various forms of spoof samples.
  • 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.
  • 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.
  • 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,” “multibiometric,” or “multifactor biometric” sensing.
  • biometric technologies are combined in such a way that different technologies measure portions 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.
  • technologies are combined in a way that they view the same part of the body they are referred to as being “tightly coupled.”
  • Embodiments of the invention provide methods and systems for performing biometric functions.
  • Image-texture measures are used to enable texture biometrics in which biometric functions are performed through an analysis of texture characteristics of skin sites.
  • a method is provided of performing a biometric function.
  • a purported skin site of an individual is illuminated with illumination light.
  • the purported skin site is in contact with a surface.
  • Light scattered from the purported skin site is received substantially in a plane that includes the surface.
  • An image is formed from the received light.
  • An image-texture measure is generated from the image.
  • the generated image-texture measure is analyzed to perform the biometric function.
  • the biometric function comprises an antispoofmg function; in such embodiments the image-texture measure is analyzed to determine whether the purported skin site comprises living tissue, hi other embodiments, the biometric function comprises an identity function; in such embodiments, the image-texture measure is analyzed to determine an identity of the individual.
  • the biometric function comprises a demographic or anthropometric function; in such embodiments, the image- texture measure is analyzed to estimate a demographic or anthropometric characteristic of the individual.
  • the surface may be the surface of an imaging detector, with light scattered from the purported skin site being received at the imaging detector.
  • a pattern of light may be translated from the plane to an imaging detector disposed outside the plane without substantial degradation or attenuation of the pattern, with the translated pattern being received at the imaging detector, hi different embodiments, the light scattered from the purported skin site may be received at a monochromatic imaging detector or at a color imaging detector.
  • the illumination light is white light.
  • the image may then comprise a plurality of images corresponding to different wavelengths.
  • the image- texture measure may accordingly be generated by performing a spatial moving- window analysis of each of the plurality of images. For instance, moving-window Fourier transforms may be calculated on the plurality of images. Alternatively, a moving-window centrality measure and a moving- window variability measure of the plurality of images maybe calculated.
  • the generated image-texture measure may be compared with a reference image- texture measure.
  • the reference image-texture measure was generated from a reference image formed from light scattered from a reference skin site with the purported skin site being substantially different from the reference skin site.
  • spectral features of the received light are compared with reference spectral features in performing the biometric function.
  • a biometric sensor comprises a surface, an illumination subsystem, a detection subsystem, and a computational unit.
  • the surface is adapted for contact with a purported skin site.
  • the illumination subsystem is disposed to illuminate the purported skin site when the purported skin site is in contact with the surface.
  • the detection subsystem is disposed to receive light scattered from the purported skin site, with the light being received substantially in a plane that includes the surface.
  • the computational unit is interfaced with the detection subsystem and has instructions for forming an image from the received light. It also has instructions for generating an image-texture measure from the image and for analyzing the generated image- texture measure to perform the biometric function.
  • the biometric function comprises an antispoofing function, with the computational unit having instructions for determining whether the purported skin site comprises living tissue, hi another embodiment, the biometric function comprises an identity function, with the computational unit having instructions for determining an identify of the individual from the generated image-texture measure. In still another embodiment, the biometric function comprises a demographic or anthropometric function, with the computational unit having instructions for estimating a demographic or anthropometric characteristic of the individual from the generated image-texture measure.
  • the biometric sensor further comprises an imaging detector, hi one such embodiment, the surface is a surface of the imaging detector, with the detection subsystem comprising the imaging detector and being configured to receive light scattered from the purported skin site at the imaging detector, hi another such embodiment, the imaging detector is disposed outside the plane.
  • An optical arrangement is configured to translate a pattern of light from the plane to the imaging detector without substantial degradation or attenuation of the pattern.
  • the detection system comprises the imaging detector and is configured to receive the translated pattern at the imaging detector.
  • the imaging detector may comprise a monochromatic imaging detector or a color imaging detector in different embodiments.
  • the illumination subsystem is configured to illuminate the purported skin site with white light.
  • the image may then comprise a plurality of images corresponding to different wavelengths, with the instructions for generating the image-texture measure comprise instructions for performing a spatial moving- window analysis of each of the plurality of images. For instance, there may be instructions for calculating moving- window Fourier transforms on the plurality of images in one embodiment, while another embodiment has instructions for calculating a moving-window centrality measure and a moving- window variability measure of the plurality of images.
  • the instructions for analyzing the generated image-texture measure to perform the biometric function comprise instructions for comparing the generated image-texture measure with a reference image-texture measure.
  • a reference image-texture measure may have been generated from a reference image formed from light scattered from a reference skin site, with the purported skin site being substantially different from the reference skin site.
  • the computational unit further has instructions for comparing spectral features of the received light with reference spectral features in performing the biometric function.
  • Embodiments of the invention provide methods and systems for performing biometric functions.
  • White light is used to illuminate a purported skin site and a color imager is used to collect light scattered from the purported skin site for the generation of multispectral data.
  • These multispectral data may be generated in the form of multiple images of the skin site collected with different illumination wavelengths, which correspond to different volumes of illuminated tissue. These data are then subjected to different types of analyses depending on specific aspects of the biometric function to be performed.
  • a biometric sensor is provided.
  • a white-light illumination subsystem is disposed to illuminate a purported skin site of an individual with white light.
  • a detection subsystem is disposed to receive light scattered from the purported skin site and comprises a color imager on which the received light is incident.
  • a computational unit is interfaced with the detection subsystem. The computational unit has instructions for deriving a plurality of spatially distributed images of the purported skin site from the received light with the color imager. The plurality of spatially distributed images correspond to different volumes of illuminated tissue of the individual.
  • the computational unit also has instructions for analyzing the plurality of spatially distributed images to perform a biometric function.
  • the biometric function comprises an antispoofing function and the instructions for analyzing the plurality of spatially distributed images comprise instructions for determining whether the purported skin site comprises living tissue.
  • the instructions for analyzing the plurality of spatially distributed images to perform the biometric function comprise instructions for analyzing the plurality of spatially distributed images to estimate a demographic or anthropometric characteristic of the individual.
  • the instructions for analyzing the plurality of spatially distributed images to perform the biometric function comprise instructions for analyzing the plurality of spatially distributed images to determine a concentration of an analyte in blood of the individual.
  • the biometric sensor may further comprise a platen in contact with the purported skin site, with the white-light illumination subsystem being adapted to illuminate the purported skin site through the platen.
  • the white-light illumination subsystem may instead be adapted to illuminate the purported skin site when the skin site is not in physical contact with the biometric sensor.
  • the white-light illumination subsystem comprises a broadband source of white light
  • the white-light illumination subsystem comprises a plurality of narrow-band light sources and an optical arrangement to combine light provided by the plurality of narrow-band light sources.
  • the plurality of narrow-band light sources may provide light at wavelengths that correspond to each of a set of primary colors. Li some cases, the purported skin site and an illumination region where the purported skin site is illuminated are in relative motion.
  • Some embodiments make use of polarization by including a first polarizing in the illumination system disposed to polarize the white light.
  • the detection system then comprises a second polarizer disposed to encounter the received light.
  • the first and second polarizers may be crossed relative to each other. In other embodiments, the first and second polarizers may be parallel. In some embodiments, the first polarizer may be omitted while retaining the second, in some embodiments, two or more of these polarization options may be combined in a single device.
  • the detection system may also sometimes include an infrared filter disposed to encounter the received light before the received light is incident on the color imager.
  • the purported skin site is a volar surface of a finger or hand and the biometric function comprises a biometric identification.
  • the instructions for analyzing the plurality of spatially distributed images comprise instructions for deriving a surface fingerprint or palmprint image of the purported skin site from the plurality of spatially distributed images. The surface fingerprint or palmprint image is then compared with a database of fingerprint or palmprint images to identify the individual.
  • the instructions for analyzing the plurality of spatially distributed images instead comprise instructions for comparing the plurality of spatially distributed images with a database of multispectral images to identify the individual.
  • a method is provided of performing a biometric function.
  • a purported skin site of an individual is illuminated with white light.
  • Light scattered from the purported skin site is received with a color imager on which the received light is incident.
  • a plurality of spatially distributed images of the purported skin site are derived, with the plurality of spatially distributed images corresponding to different volumes of illuminated tissue of the individual.
  • the plurality of spatially distributed images are analyzed to perform the biometric function.
  • the biometric function comprises an antispoofing function and analyzing the plurality of spatially distributed images comprises determining whether the purported skin site comprises living tissue.
  • the plurality of spatially distributed images are analyzed to estimate a demographic or anthropometric characteristic of the individual.
  • the plurality of spatially distributed images are analyzed to determine a concentration of an analyte in blood of the individual.
  • the purported skin site may sometimes be illuminated by directing the white light through a platen in contact with the purported skin site, hi some instances, the purported skin site may be illuminated with a broadband source of white light, while in other instances a plurality of narrow-band beams, perhaps corresponding to a set of primary colors, may be generated and combined.
  • the purported skin site might sometimes be in relative motion with an illumination region where the purported skin site is illuminated.
  • the while light is polarized with a first polarization and the received light scattered from the purported skin site is polarized with a second polarization.
  • the first and second polarizations may be substantially crossed relative to each other or may be substantially parallel to each other.
  • the received light may sometimes be filtered at infrared wavelengths before the received light is incident on the color imager.
  • the biometric function comprises a biometric identification.
  • the purported skin site could be a volar surface of a finger or hand.
  • Analysis of the plurality of spatially distributed images could then proceed by deriving a surface fingerprint or palmprint image of the purported skin site from the plurality of spatially distributed images and comparing the surface fingerprint or palmprint image with a database of fingerprint or palmprint images.
  • the plurality of spatially distributed images could be compared with a database of multispectral images to identify the individual.
  • 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.
  • Fig. 1 provides a front view of a noncontact biometric sensor in one embodiment of the invention
  • FIG. 2A provides an illustration of a structure for a Bayer color filter array, which may be used in embodiments of the invention
  • Fig. 2B is a graph showing color response curves for a Bayer color filter array like that illustrated in Fig. 2A;
  • FIG. 3 provides a front view of a noncontact biometric sensor in another embodiment of the invention.
  • Fig. 4 provides a top view of a sensor configuration that collects data during relative motion between a skin site and an optically active region of the sensor;
  • Fig. 5 illustrates a multispectral datacube that may be used in certain embodiments of the invention
  • FIG. 6 is a front view of a contact biometric sensor in one embodiment of the invention.
  • Fig. 7 A provides a side view of a contact biometric sensor in an embodiment
  • Fig. 7B provides a side view of a contact biometric sensor in another embodiment
  • Fig. 8 provides a front view of a contact biometric sensor in a further embodiment of the invention
  • Fig. 9A illustrates a structure for a contact texture biometric sensor in an embodiment of the invention
  • Fig. 9B provides a side view of a contact texture biometric sensor in one configuration
  • Fig. 9C provides a side view of a contact texture biometric sensor in another configuration
  • FIG. 10 is schematic representation of a computer system that may be used to manage functionality of contact and noncontact biometric sensors in accordance with embodiments of the invention
  • Fig. 11 is a flow diagram summarizing methods of using contact and noncontact biometric sensors and illustrates a number of different biometric functions that may be performed.
  • Fig. 12 is a flow diagram summarizing methods of operation of contact texture biometric sensors in accordance with embodiments of the invention.
  • Embodiments of the invention provide methods and systems that allow for the collection and processing of a variety of different types of biometric measurements, including integrated, multifactor biometric measurements in some embodiments. These measurements may provide strong assurance of a person's identity, as well as of the authenticity of the biometric sample being taken, hi some embodiments, a sensor uses white light that penetrates the surface of the person's skin, and scatters within the skin and/or the underlying tissue.
  • white light refers to light that has a spectral composition amenable to separation into constituent wavelength bands, which in some cases may comprise primary colors. The usual primary colors used to define white light are red, green, and blue, but other combinations may be used in other instances, as will be known to those of skill in the art.
  • white light might not appear white to a human observer and might have a distinct tint or color associated with it because of the exact wavelength distribution and intensity of the constituent wavelength bands.
  • the white light may comprise one or more bands in the ultraviolet or infrared spectral regions.
  • the white light might not even be visible at all to a human observer when it consists of wavelength bands in the infrared and/or ultraviolet spectral regions.
  • a portion of the light scattered by the skin and/or underlying tissue exits the skin and is used to form an image of the structure of the tissue at and below the surface of the skin.
  • the image formed from each wavelength of light comprised by the white light may be different from images formed at other wavelengths. Accordingly, embodiments of the invention collect images in such a way that characteristic spectral and spatial information may be extracted from the resulting image.
  • an ability is provided to measure analyte levels of a person simultaneously with measurement of a fingerprint pattern.
  • the measure analyte comprises a blood-alcohol level of the person; such embodiments also enable a variety of commercial applications that include restricting motor-vehicle access. In this way, the analyte measurement and the identity of the person on whom the measurement is made may be inextricably linked.
  • Skin composition and structure is very distinct, very complex, and varies from person to person.
  • a number of assessments may be made. For example, a biometric- identification function may be performed to identify or verify whose skin is being measured, a liveness function may be performed to assure that the sample being measured is live and viable skin and not another type of material, estimates may be made of a variety of physiological parameters such as age gender, ethnicity, and other demographic and anthropometric characteristics, and/or measurements may be made of the concentrations of various analytes and parameters including alcohol, glucose, degrees of blood perfusion and oxygenation, biliruben, cholesterol, urea, and the like.
  • the complex structure of skin may be used in different embodiments to tailor aspects of the methods and systems for particular functions.
  • the outermost layer of skin, the epidermis is supported by the underlying dermis and hypodermis.
  • the epidermis itself may have five identified sublayers that include the stratum corneum, the stratum lucidum, the stratum granulosum, the stratum spinosum, and the stratum germinativum.
  • the skin below the top-most stratum corneum has some characteristics that relate to the surface topography, as well as some characteristics that change with depth into the skin.
  • the dermis While the blood supply to skin exists in the dermal layer, the dermis has protrusions into the epidermis known as "dermal papillae," which bring the blood supply close to the surface via capillaries. In the volar surfaces of the fingers, this capillary structure follows the pattern of the friction ridges and valleys on the surface. In some other locations on the body, the structure of the capillary bed may be less ordered, but is still characteristic of the particular location and person. As well, the topography of the interface between the different layers of skin is quite complex and characteristic of the skin location and the person.
  • inks, dyes and/or other pigmentation may be present in portions of the skin as topical coating or subsurface tattoos. These forms of artificial pigmentation may or may not be visible to the naked human eye. However, if one or more wavelengths used by the apparatus of the present invention is sensitive to the pigment, the sensor can be used in some embodiments to verify the presence, quantity and/or shape of the pigment in addition to other desired measurement tasks.
  • embodiments of the present invention provide methods and systems that collect spatiospectral information that may be represented in a multidimensional data structure that has independent spatial and spectral dimensions.
  • the desired information is contained in just a portion of the entire multidimensional data structure.
  • estimation of a uniformly distributed, spectrally active compound may require just the measured spectral characteristics, which may be extracted from the overall multidimensional data structure.
  • the overall system design may be simplified to reduce or eliminate the spatial component of the collected data by reducing the number of image pixels, even to a limit of a single pixel.
  • the systems and methods disclosed are generally described in the context of spatiospectral imaging, it will be recognized that the invention encompasses similar measurements in which the degree of imaging is greatly reduced, even to the point where there is a single detector element.
  • FIG. 1 shows a front view of a noncontact biometric sensor 101.
  • the sensor 101 comprises an illumination subsystem 121 having one or more light sources 103 and a detection subsystem 123 with an imager 115.
  • the figure depicts an embodiment in which the illumination subsystem 121 comprises a plurality of illumination subsystems 121a and 121b, but the invention is not limited by the number of illumination or detection subsystems 121 or 123.
  • the number of illumination subsystems 121 may conveniently be selected to achieve certain levels of illumination, to meet packaging requirements, and to meet other structural constraints of the sensor 101.
  • Illumination light passes from the source 103 through illumination optics 105 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.
  • the illumination light is provided as polarized light, such as by disposing a linear polarizer 107 through which the light passes before striking a finger 119 or other skin site of the person being studied.
  • a linear polarizer 107 through which the light passes before striking a finger 119 or other skin site of the person being studied.
  • the imaged skin site may be positioned to interact with the light without being in contact with any solid surface.
  • the imaged skin site is in contact with some solid surface such as a platen or light detector.
  • the light source 103 comprises a white-light source, which may be provided as a broad-band source or as a collection of narrow-band emitters in different embodiments.
  • broad-band sources include white-light emitting diodes ("LEDs"), incandescent bulbs or glowbars, and the like.
  • Collections of narrow-band emitters may comprise quasimonochromatic light sources having primary-color wavelengths, such as in an embodiment that includes a red LED or laser diode, a green LED or laser diode, and a blue LED or laser diode.
  • optical polarizers Both linear and circular polarizers can be employed advantageously to make the optical measurement more sensitive to certain skin depths, as known to on familiar in the art.
  • the illumination light is polarized by linear polarizer 107.
  • the detection subsystem 123 may then also include a linear polarizer 111 that is arranged with its optical axis substantially orthogonal to the illumination polarizer 107. In this way, light from the sample must undergo multiple scattering events to significantly change it state of polarization. Such events occur when the light penetrates the surface of the skin and is scattered back to the detection subsystem 123 after many scatter events.
  • two polarizers 107 and 111 may also be used to increase the influence of directly reflected light by arranging the polarizer 111 to be substantially parallel to polarizer 107.
  • either polarizer 107 or 111, or both may be omitted, allowing for the collection of substantially randomly polarized light.
  • the detection subsystem 123 may incorporate detection optics that comprise lenses, mirrors, phase plates and wavefront coding devices, and/or other optical elements that form an image onto the detector 115.
  • the detection optics 113 may also comprise a scanning mechanism (not shown) to relay portions of the overall image onto the detector 115 in sequence.
  • the detection subsystem 123 is configured to be sensitive to light that has penetrated the surface of the skin and undergone optical scattering within the skin and/or underlying tissue before exiting the skin.
  • the detector 115 may comprise a
  • the detector subsystem 123 may additionally comprise an infrared filter 114 disposed to reduce the amount of infrared light detected.
  • the filter array may allow the transmission of infrared light.
  • an infrared filter 114 may be omitted and one or more light sources 103 that emit infrared light may be incorporated. In this way, all color filter elements 204, 208, and 212 may allow the light to substantially pass through, resulting in an infrared image across the entire detector 115.
  • the biometric sensor 301 comprises an illumination subsystem 323 and a detection subsystem 325. Similar to the embodiment described in connection with Fig. 1, there may be multiple illumination subsystems 323 in some embodiments, with Fig. 3 showing a specific embodiment having two illumination subsystems 323.
  • a white-light source 303 comprised by the illumination subsystem 323 may be any source of white light, including the broad-band or combination of narrow-band sources described above. Light from the white-light source 303 passes through illumination optics 305 and a linear polarizer 307 before passing into the skin site 119.
  • a portion of the light is diffusely reflected from the skin site 119 into the detection subsystem 325, which comprises imaging optics 315 and 319, a linear polarizer 311, and a dispersive optical element 313.
  • the dispersive element 313 may comprise a one- or two-dimensional grating, which may be transmissive or reflective, a prism, or any other optical component known in the art to cause a deviation of the path of light as a function of the light's wavelength.
  • the first imaging optics 319 acts to collimate light reflected from the skin site 119 for transmission through the linear polarizer 311 and dispersive element 313.
  • Spectral components of the light are angularly separated by the dispersive element 313 and are separately focused by the second imaging optics 315 onto a detector.
  • polarizers 307 and 311 respectively comprised by the illumination and detection subsystems 323 and 325 act to reduce the detection of directly reflected light at the detector 317.
  • the polarizers 307, 311 may also be oriented such that their optical axes are substantially parallel, which will increase the detection of directly reflected light at the detector 317. In some embodiments, either polarizer 307 or 311 , or both, may be omitted.
  • the image generated from light received at the detector is thus a "coded” image in the manner of a computer tomographic imaging spectrometer ("CTIS"). Both spectral and spatial information are simultaneously present in the resulting image.
  • CTIS computer tomographic imaging spectrometer
  • Both spectral and spatial information are simultaneously present in the resulting image.
  • the individual spectral patters may be obtained by mathematical inversion or "reconstruction" of the coded image.
  • a scanner mechanism may be provided to scan the illumination light.
  • the image may be constructed by building up separate image portions collected during the relative motion.
  • Such relative motion may also be achieved in embodiments that configure the sensor in a swipe configuration, in which the user is instructed to translate the skin site.
  • a swipe sensor is shown in top view with the schematic illustration of Fig. 4.
  • the illumination region and detection region 405 of a sensor 401 are substantially collinear. In some embodiments of a swipe sensor 401, there may be more than a single illumination region.
  • a swipe sensor may be implemented with any of the contactless sensor configurations described above, although in some implementations it may be used with a contact configuration, examples of which are described in detail below.
  • the light that is received sequentially from discrete portions of the skin site is used to build up the image that is subsequently used for biometric applications.
  • the embodiments described above produce a body of spatio-spectral data, which may be used in biometrics applications as described below.
  • the invention is not limited to any particular manner of storing or analyzing the body of spatio-spectral data.
  • it is shown in the form of a datacube in Fig. 5.
  • the datacube 501 is shown decomposed along a spectral dimension with a plurality of planes 503, 505, 507, 509, 511, each of which corresponds to a different portion of the light spectrum and each of which include spatial information.
  • the body of spatio-spectral data may include additional types of information beyond spatial and spectral information.
  • multispectral data data collected under a plurality of optical conditions, whether they be collected simultaneously or sequentially, is referred to herein as “multispectral” data.
  • multispectral data data collected under a plurality of optical conditions, whether they be collected simultaneously or sequentially, is referred to herein as “multispectral” data.
  • a more complete description of aspects of multispectral data is described in copending, commonly assigned U.S. Pat. Appl. No. 11/379,945, entitled “MULTISPECTRAL BIOMETRIC SENSORS,” filed April 24, 2006, the entire disclosure of which is incorporated herein by reference for all purposes.
  • Spatio-spectral data may thus be considered to be a subset of certain types of multispectral data where the different optical conditions include different illumination wavelengths.
  • the images 503, 505, 507, 509, and 511 might correspond, for example to images generated using light at 450 nm, 500 nm, 550 nm, 600 nm, and 650 nm .
  • Each image represents the optical effects of light of a particular wavelength interacting with skin. Due to the optical properties of skin and skin components that vary by wavelength, each of the multispectral images 503, 505, 507, 509, and 511 will be, in general, different from the others.
  • the datacube may thus be expressed as R(Xs , Ys, Xi , Y 1 , ty and describes the amount of diffusely reflected light of wavelength ⁇ seen at each image point Xi, Yj when illuminated at a source point Xs, Ys- Different illumination configurations (flood, line, etc.) can be summarized by summing the point response over appropriate source point locations.
  • a conventional non-TIR fingerprint image F(Xj , Yj) can loosely be described as the multispectral data cube for a given wavelength, ⁇ > , and summed over all source positions:
  • the spectral biometric dataset S(K) relates the measured light intensity for a given wavelength ⁇ to the difference D between the illumination and detection locations:
  • the datacube R is thus related to both conventional fingerprint images and to spectral biometric datasets.
  • the datacube R is a superset of either of the other two data sets and contains correlations and other information that may be lost in either of the two separate modalities.
  • the light that passes into the skin and/or underlying tissue is generally affected by different optical properties of the skin and/or underlying tissue at different wavelengths.
  • Two optical effects in the skin and/or underlying tissue that are affected differently at different wavelengths are scatter and absorbance.
  • Optical scatter in skin tissue is generally a smooth and relatively slowly varying function wavelength.
  • absorbance in skin is generally a strong function of wavelength due to particular absorbance features of certain components present in the skin. For example blood, melanin, water, carotene, biliruben, ethanol, and glucose all have significant absorbance properties in the spectral region from 400 run to 2.5 ⁇ m, which may sometimes be encompassed by the white- light sources.
  • the combined effect of optical absorbance and scatter causes different illumination wavelengths to penetrate the skin to different depths.
  • the capillary layers close to the surface of the skin have distinct spatial characteristics that can be imaged at wavelengths where blood is strongly absorbing.
  • the set of spectral values corresponding to a given image location has spectral characteristics that are well-defined and distinct. These spectral characteristics may be used to classify the collected image on a pixel-by-pixel basis. This assessment may be performed by generating typical tissue spectral qualities from a set of qualified images. For example, the spatio-spectral data shown in Fig.
  • N x 5 may be reordered as an N x 5 matrix, where N is the number of image pixels that contain data from living tissue, rather than from a surrounding region of air.
  • An eigenanalysis or other factor analysis performed on this set matrix produces the representative spectral features of these tissue pixels.
  • the spectra of pixels in a later data set may then be compared to such previously established spectral features using metrics such as Mahalanobis distance and spectral residuals. If more than a small number of image pixels have spectral qualities that are inconsistent with living tissue, then the sample is deemed to be non-genuine and rejected, thus providing a mechanism for incorporating antispoofing methods in the sensor based on determinations of the liveness of the sample.
  • textural characteristics of the skin may alone or in conjunction with the spectral characteristics be used to determine the authenticity of the sample.
  • each spectral image may be analyzed in such a way that the magnitude of various spatial characteristics may be described. Methods for doing so include wavelet transforms, Fourier transforms, cosine transforms, gray-level co-occurrence, and the like. The resulting coefficients from any such transform described an aspect of the texture of the image from which they were derived. The set of such coefficients derived from a set of spectral images thus results in a description of the chromatic textural characteristics of the multispectral data. These characteristics may then be compared to similar characteristics of known samples to perform a biometric determination such as spoof or liveness determination. Methods for performing such determinations are generally similar to the methods described for the spectral characteristics above. Applicable classification techniques for such determinations include linear and quadratic discriminant analysis, classification trees, neural networks, and other methods known to those familiar in the art.
  • the image pixels may be classified as "ridge,” “valley,” or “other” based on their spectral qualities or their chromatic textural qualities.
  • This classification can be performed using discriminant analysis methods such as linear discriminant analysis, quadratic discriminant analysis, principal component analysis, neural networks, and others known to those of skill in the art. Since ridge and valley pixels are contiguous on a typical volar surface, in some instances, data from the local neighborhood around the image pixel of interest are used to classify the image pixel. In this way, a conventional fingerprint image may be extracted for further processing and biometric assessment.
  • the "other" category may indicate image pixels that have spectral qualities that are different than anticipated in a genuine sample.
  • a threshold on the total number of pixels in an image classified as "other” may be set. If this threshold is exceeded, the sample may be determined to be non-genuine and appropriate indications made and actions taken.
  • multispectral data collected from regions such as the volar surface of fingers may be analyzed to directly estimate the locations of "minutiae points," which are defined as the locations at which ridges end, bifurcate, or undergo other such topographic change.
  • the chromatic textural qualities of the multispectral dataset may be determined in the manner described above. These qualities may then be used to classify each image location as "ridge ending,” “ridge bifurcation,” or “other” in the manner described previously.
  • minutiae feature extraction may be accomplished directly from the multispectral data without having to perform computationally laborious calculations such as image normalization, image binarization, image thinning, and minutiae filtering, techniques that are known to those familiar in the art.
  • Biometric determinations of identity may be made using the entire body of spatio-spectral data or using particular portions thereof. For example, appropriate spatial filters may be applied to separate out the lower spatial frequency information that is typically representative of deeper spectrally active structures in the tissue.
  • the fingerprint data may be extracted using similar spatial frequency separation and/or the pixel-classification methods disclosed above.
  • the spectral information can be separated from the active portion of the image in the manner discussed above.
  • These three portions of the body of spatio-spectral data may then be processed and compared to the corresponding enrollment data using methods known to one familiar in the art to determine the degree of match. Based upon the strength of match of these characteristics, a decision can be made regarding the match of the sample with the enrolled data.
  • ethanol has characteristic absorbance peaks at approximately 2.26 ⁇ m, 2.30 ⁇ m, and 2.35 ⁇ m, and spectral troughs at 2.23 ⁇ m, 2.28 ⁇ m, 2.32 ⁇ m, and 2.38 ⁇ m.
  • noninvasive optical measurements are performed at wavelengths in the range of 2.1 - 2.5 ⁇ m, more particularly in the range of 2.2 - 2.4 ⁇ m.
  • the resulting spectral data are analyzed using multivariate techniques such as partial least squares, principal-component regression, and others known to those of skill in the art, to provide an estimate of the concentration of alcohol in the tissue, as well as to provide a biometric signature of the person being tested. While a correlation to blood-alcohol level may be made with values determined for a subset of these wavelengths, it is preferable to test at least the three spectral peak values, with more accurate results being obtained when the seven spectral peak and trough values are measured.
  • noninvasive optical measurements are performed at wavelengths in the range of 1.5 - 1.9 ⁇ m, more particularly in the range of 1.6 - 1.8 ⁇ m.
  • optical measurements are performed at one or more wavelengths of approximately 1.67 ⁇ m, 1.69 ⁇ m, 1.71 ⁇ m, 1.73 ⁇ m, 1.74 ⁇ m 1.76 ⁇ m and 1.78 ⁇ m.
  • the presence of alcohol is characterized at these wavelengths by spectral peaks at 1.69 ⁇ m, 1.73 ⁇ m, and 1.76 ⁇ m and by spectral troughs at 1.67 ⁇ m, 1.71 ⁇ m, 1.74 ⁇ m, and 1.78 ⁇ m.
  • the concentration of alcohol is characterized by relative strengths of one or more of the spectral peak and trough values. Also, while a correlation to blood-alcohol level may be made with values determined for a subset of these wavelengths in the 1.5 - 1.9 ⁇ m range, it is preferable to test at least the three spectral peak values, with more accurate results being obtained when the seven spectral peak and trough values are measured.
  • a small spectral alcohol-monitoring device may be embedded in a variety of systems and applications in certain embodiments.
  • the spectral alcohol-monitoring device can be configured as a dedicated system such as may be provided to law-enforcement personnel, or maybe integrated as part of an electronic device such as an electronic fob, wristwatch, cellular telephone, PDA, or any other electronic device, for an individual's personal use.
  • Such devices may include mechanisms for indicating to an individual whether his blood- alcohol level is within defined limits.
  • the device may include red and green LEDs, with electronics in the device illuminating the green LED if the individual's blood-alcohol level is within defined limits and illuminating the red LED if it is not.
  • the alcohol-monitoring device may be included in a motor vehicle, typically positioned so that an individual may conveniently place tissue, such as a fingertip, on the device. While in some instances, the device may function only as an informational guide indicating acceptability to drive, in other instances ignition of the motor vehicle may affirmatively depend on there being a determination that the individual has a blood-alcohol level less than a prescribed level.
  • Biometric sensors may be constructed in a fashion similar to that shown in
  • Figs. 1 and 3 but configured so that the skin site is placed in contact with a platen.
  • Such designs have certain additional characteristics that result from the interaction of light with the platen, sometimes permitting additional information to be incorporated as part of the collect spatio-spectral data.
  • Fig. 6 provides a front view of a contact biometric sensor 601.
  • the contact sensor 601 has one or more illumination subsystems 621 and a detection subsystem 623.
  • Each of the illumination subsystems 621 comprises one or more white-light sources 603 and illumination optics that shape the light provided by the sources 603 into a desired form.
  • the illumination optics may generally include any combination of optical elements and may sometimes include a scanner mechanism.
  • the illumination light is provided as polarized light by disposing a polarizer 607 through which the illumination light passes. Examples of white-light sources 603, including broad- and narrow-band sources were described above, and the sources 603 may be configured to provide sources having different shapes in different embodiments.
  • the illumination light is directed by the illumination optics 621 to pass through a platen 617 and illuminate the skin site 119.
  • the sensor layout 601 and components may advantageously be selected to minimize the direct reflection of the illumination optics 621.
  • such direct reflections are reduced by relatively orienting the illumination subsystem 621 and detection subsystem 623 such that the amount of directly reflected light detected is minimized.
  • optical axes of the illumination subsystem 621 and the detection subsystem 623 may be placed at angles such that a mirror placed on the platen 617 does not direct an appreciable amount of illumination light into the detection subsystem 623.
  • optical axes of the illumination and detection subsystems 621 and 623 may be placed at angles relative to the platen 617 such that the angular acceptance of both subsystems is less than the critical angle of the system 601; such a configuration avoids appreciable effects due to total internal reflectance between the platen 617 and the skin site 119.
  • the detection subsystem 623 may include a polarizer 611 having an optical axis substantially orthogonal or parallel to the polarizer 607 comprised by the illumination subsystem 621. Surface reflections at the interface between the platen 617 and the skin site 119 are reduced in the case where polarizers 611 and 607 are oriented substantially orthogonal to each other since light from the sample must undergo sufficiently many scattering events to change its state of polarization before it can be sensed by the detector 615.
  • the detection subsystem 623 may additionally incorporate detection optics that form an image of the region near the platen surface 617 onto the detector 615.
  • the detection optics 613 comprise a scanning mechanism (not shown) to relay portions of the platen region onto the detector 615 in sequence.
  • An infrared filter 614 may be included to reduce the amount of infrared light detected, particularly in embodiments where the detector 615 is sensitive to infrared light, such as when a Bayer filter array is used.
  • the infrared filter 614 may be omitted in some embodiments and an additional light source 603 with emissions in the infrared may be included in some embodiments.
  • the detection subsystem 623 is generally configured to be sensitive to light that has penetrated the surface of the skin and undergone optical scattering within the skin and/or underlying tissue.
  • the polarizers may sometimes be used to create or accentuate the surface features. For instance, if the illumination light is polarized in a direction parallel (“P") with the platen 617, and the detection subsystem 623 incorporates a polarizer 611 in a perpendicular orientation ("S”), then the reflected light is blocked by as much as the extinction ratio of the polarizer pair.
  • FIG. 7A A side view of one of the embodiments of the invention is shown with the schematic drawing provided in Fig. 7A. For clarity, this view does not show the detection subsystem, but does show an illumination subsystem 621 explicitly.
  • the illumination subsystem 621 in this embodiment has a plurality of white- light sources 703 that are distributed spatially. As shown in the drawing, the illumination optics 621 are configured to provide flood illumination, but in alternative embodiments could be arranged to provide line, point, or other patterned illumination by incorporation of cylindrical optics, focusing optics, or other optical components as known to those knowledgeable in the art.
  • the array of white-light sources 703 in Fig. 7A need not actually be planar as shown in the drawing.
  • optical fibers, fiber bundles, or fiber optical faceplates or tapers could convey the light from the light sources at some convenient locations to an illumination plane, where light is reimaged onto the skin site 119.
  • the light sources could be controlled turning the drive currents on and off as LEDs might be.
  • switching of the light may be accomplished using some form of spatial light modulator such as a liquid crystal modulator or using microelectromechanical-systems (“MEMS”) technology to control apertures, mirrors, or other such optical elements.
  • MEMS microelectromechanical-systems
  • Fig. 7B shows the use of optical fibers and electronic scanning of illumination sources such as LEDs.
  • Individual fibers 716a connect each of the LEDs located at an illumination array 710 to an imaging surface, and other fibers 716b relay the reflected light back to the imaging device 712, which may comprise a photodiode array, CMOS array, or CCD array.
  • the set of fibers 716a and 716b thus defines an optical fiber bundle 714 used in relaying light.
  • the biometric sensor 801 comprises one or more white- light illumination subsystems 823 and a detection subsystem 825.
  • the illumination subsystems 823 comprise a white-light source 803 that provides light that passes through illumination optics 805 and a polarizer 807 to be directed to a platen 817 over which a skin site is disposed 119.
  • a portion of the light is diffusely reflected from the skin site 119 into the detection subsystem 825, which comprises imaging optics 815 and 819, a crossed polarizer 811, and a dispersive optical element 813.
  • the first imaging optics 819 collimate light reflected from the skin site 119 for transmission through the crossed polarizer 811 and dispersive element 813. Separated spectral components are separately focused onto the detector 817 by the second imaging optics 815.
  • Contact biometric sensors like those illustrated in Figs. 6 - 8 are also amenable to configurations in which the illumination region is in relative motion with the skin site.
  • such relative motion may be implemented with a mechanism for scanning the illumination light and/or by moving the skin site.
  • the presence of a platen in contact-sensor embodiments generally facilitates motion of the skin site by confining a surface of the skin site to a defined plane; in embodiments where freedom of motion is permitted in three dimensions, additional difficulties may result from movement of the skin site outside the imaging depth.
  • a swipe sensor may accordingly be implemented with contact biometric sensors in a fashion as generally described in connection with Fig. 4 above, but with a platen that prevents motion of the skin site in one direction.
  • the swipe sensor may be a stationary system
  • a contact configuration allows a roller system to be implemented in which the skin site is rolled over a roller structure that is transparent to the white light.
  • An encoder may record position information and aid in stitching a full two-dimensional image from a resulting series of image slices, as understood by those of skill in the art. Light received from discrete portions of the skin site is used to build up the image.
  • noncontact and contact biometric sensors have focused on embodiments in which white light is used, other embodiments may make use of other spectral combinations of light in similar structural arrangements.
  • other embodiments may include additional variations in optical conditions to provide multispectral conditions.
  • Some description of such multispectral applications is provided in commonly assigned U.S. Pat. Appl. No. 10/818,698, entitled “MULTISPECTRAL BIOMETRIC SENSOR,” filed April 5, 2004 by Robert K. Rowe et al; U.S. Pat. 11/177,817, entitled “L ⁇ VENESS SENSOR,” filed July 8, 2005 by Robert K. Rowe; U.S. Prov. Pat. No.
  • 60/576,364 entitled “MULTISPECTRAL FINGER RECOGNITION,” filed June 1, 2004 by Robert K. Rowe and Stephen P. Corcoran; U.S. Prov. Pat. Appl. No. 60/600,867, entitled “MULTISPECTRAL IMAGING BIOMETRIC,” filed August 11, 2004 by Robert K. Rowe; U.S. Pat. No. 11/115,100, entitled “MULTISPECTRAL IMAGING BIOMETRICS,” filed April 25, 2005 by Robert K. Rowe; U.S. Pat. Appl. No. 11/115,101, entitled
  • the noncontact and contact biometric sensors described above use white- light imaging in certain embodiments.
  • the use of white light permits images to be collected simultaneously at multiple colors, with the overall speed of data collection being faster than in embodiments where discrete states are collected separately.
  • This reduced data-collection time leads to a reduction in motion artifacts as the skin site moves during data collection.
  • the overall sensor size may also be reduced and provided at lower cost by using a smaller number of light sources when compared with the use of discrete illumination sources for different colors.
  • Corresponding reductions are also possible in the electronics used to support coordinated operation of the light sources.
  • color imagers are currently available at prices that are typically lower than monochrome imagers.
  • a typical design criterion may provide a 1-inch field with a 500 dots-per-inch resolution. This can be achieved with a monochrome camera having 500 ⁇ 500 pixels. It can also be achieved with a 1000 x 1000 color camera when extracting each color plane separately. The same resolution can be achieved by using a 500 x 500 color imager and converting to ⁇ R, G, B ⁇ triplets and then extracting the monochrome portion of the image.
  • texture biometric sensor refers generally to any of a large number of metrics that describe some aspect of a spatial distribution of tonal characteristics of an image, some of which were described above. For example, some textures, such as those commonly found in fingerprint patterns or wood grain, are flowlike and may be well described by metrics such as an orientation and coherence. For textures that have a spatial regularity (at least locally), certain characteristics of the Fourier transform and the associated power spectrum are important such as energy compactness, dominant frequencies and orientations, etc. Certain statistical moments such as mean, variance, skew, and kurtosis may be used to describe texture.
  • Moment invariants may be used, which are combinations of various moments that are invariant to changes in scale, rotation, and other perturbations.
  • Gray-tone spatial dependence matrices may be generated and analyzed to describe image texture. The entropy over an image region may be calculated as a measure of image texture.
  • wavelet transforms may be used to describe aspects of the image texture.
  • Steerable pyramids, Gabor filters, and other mechanisms of using spatially bounded basis functions may be used to describe the image texture.
  • Image texture may thus be manifested by variations in pixel intensities across an image, which may be used in embodiments of the invention to perform biometric functions.
  • additional information may be extracted when such textural analysis is performed for different spectral images extracted from a multispectral data set, producing a chromatic textural description of the skin site.
  • biometric matching may be performed statistically instead of requiring a match to a deterministic spatial pattern.
  • the sensor may be configured in a compact manner because it need not acquire an image over a specified spatial area.
  • the ability to provide a small sensor also permits the sensor to be made more economically than sensors that need to collect complete spatial information to perform a biometric function.
  • biometric functions may be performed with purely spectral information, while in other embodiments, spatio-spectral information is used.
  • the sensor 900 comprises a plurality of light sources 904 and an imager 908.
  • the light sources 904 comprise white-light sources, although in other embodiments, the light sources comprise quasimonochromatic sources.
  • the imager 908 may comprise a monochromatic or color imager, one example of which is an imager having a Bayer pattern.
  • the sensor 900 is referred to herein as a "contact" sensor because the image is collected substantially in the plane of the skin site 119 being measured. It is possible, however, to have different configurations for operating the sensor, some with the imager 908 substantially in contact with the skin site 119 and some with the imager 908 displaced from the plane of the skin site 119.
  • Figs. 9B and 9C This is shown for two illustrative embodiments in Figs. 9B and 9C.
  • the imager 908 is substantially in contact with the skin site 119.
  • Light from the sources 904 propagates beneath the tissue of the skin site 119, permitting light scattered from the skin site 119 and in the underlying tissue to be detected by the imager 908.
  • An alternative embodiment in which the imager 908 is displaced from the skin site 119 is shown schematically in Fig. 9C.
  • the sensor 900' includes an optical arrangement 912 that translates an image at the plane of the skin site 119 to the imager could comprise a plurality of optical fibers, which translate individual pixels of an image by total internal reflection along the fiber without substantially loss of intensity.
  • the light pattern detected by the imager 908 is substantially the same as the light pattern formed at the plane of the skin site 119.
  • the sensor 900' may thus operate in substantially the same fashion as the sensor 900 shown in Fig. 9B. That is, light from the sources 904 is propagated to the skin site, where it is reflected and scattered by underlying tissue after penetrating the skin site 119. Because information is merely translated substantially without loss, the image formed by the imager 908 in such an embodiment is substantially identical to the image that would be formed with an arrangement like that in Fig. 9A.
  • spectral characteristics in the received data are identified and compared with an enrollment database of spectra.
  • the resultant tissue spectrum of a particular individual includes unique spectral features and combinations of spectral features that can be used to identify individuals once a device has been trained to extract the relevant spectral features. Extraction of relevant spectral features may be performed with a number of different techniques, including discriminant analysis techniques. While not readily apparent in visual analysis of a spectral output, such analytical techniques can repeatably extract unique features that can be discriminated to perform a biometric function. Examples of specific techniques are disclosed in commonly assigned U.S. Pat. No.
  • the ability to perform biometric functions with image-texture information may exploit the fact that a significant portion of the signal from a living body is due to capillary blood.
  • a known physiological characteristic is that the capillaries in the finger follow the pattern of the external fingerprint ridge structure. Therefore, the contrast of the fingerprint features relative to the illumination wavelength is related to the spectral features of blood.
  • the contrast of images taken with wavelengths longer than about 580 nm are significantly reduced relative to those images taken with wavelengths less than about 580 nm.
  • Fingerprint patterns generated with nonblood pigments and other optical effects such as Fresnel reflectance have a different spectral contrast.
  • Light scattered from a skin site 119 may be subjected to variety of different types of comparative texture analyses in different embodiments. Some embodiments make use of a form of moving-window analysis of image data derived from the collected light to generate a figure of merit, and thereby evaluate the measure of texture or figure of merit.
  • the moving window operation may be replaced with a block-by-block or tiled analysis.
  • a single region of the image or the whole image may be analyzed at one time.
  • fast-Fourier transforms are performed on one or more regions of the image data.
  • An in-band contrast figure of merit C is generated in such embodiments as the ratio of the average or DC power to in-band power. Specifically, for an index i that corresponds to one of a plurality of wavelengths comprised by the white light, the contrast figure of merit is
  • F t ( ⁇ , ⁇ ) is the Fourier transform of the image f t (x,y) at the wavelength corresponding to index i, where x and y are spatial coordinates for the image.
  • the range defined by R ⁇ ow and i? h i gh represents a limit on spatial frequencies of interest for fingerprint features.
  • R ⁇ ow may be approximately 1.5 fringes/mm in one embodiment and i? h i gh may be 3.0 fringes/mm.
  • the contrast figure of merit may be defined as the ratio of the integrated power in two different spatial frequency bands. The equation shown above is a specific case where one of the bands comprises only the DC spatial frequency.
  • moving- window means and moving- window standard deviations are calculated for the collected body of data and used to generate the figure of merit.
  • the moving- window mean ⁇ / and the moving-window standard deviation ⁇ / are calculated from the collected image/ (x, y).
  • the moving windows for each calculation may be the same size and may conveniently be chosen to span on the order of 2 - 3 fingerprint ridges.
  • the window size is sufficiently large to remove the fingerprint features but sufficiently small to have background variations persist.
  • the figure of merit C 1 in this embodiment is calculated as the ratio of the moving- window standard deviation to the moving- window mean:
  • a similar process is performed but a moving- window range (i.e., max (image values) - min(image values) ) is used instead of a moving- window standard deviation.
  • a moving- window mean ⁇ / and a moving-window range ⁇ / are calculated from the collected image f t (x, y) for each wavelength corresponding to index i.
  • the window size for calculation of the moving- window mean is again preferably large enough to remove the fingerprint features but small enough to maintain background variations.
  • the window size for calculation of the moving- window mean is the same as for calculation of the moving- window range, a suitable value in one embodiment spanning on the order of 2 - 3 fingerprint ridges.
  • the figure of merit in this embodiment is calculated as the ratio of the moving- window mean: [0107]
  • This embodiment and the preceding one may be considered to be specific cases of a more general embodiment in which moving-window calculations are performed on the collected data to calculate a moving-window centrality measure and a moving- window variability measure.
  • the specific embodiments illustrate cases in which the centrality measure comprises an unweighted mean, but may more generally comprise any other type of statistical centrality measure such as a weighted mean or median in certain embodiments.
  • the specific embodiments illustrate cases in which the variability measure comprises a standard deviation or a range, but may more generally comprise any other type of statistical variability measure such as a median absolute deviation or standard error of the mean in certain embodiments.
  • a wavelet analysis may be performed on each of the spectral images, hi some embodiments, the wavelet analysis may be performed in a way that the resulting coefficients are approximately spatially invariant. This may be accomplished by performing an undecimated wavelet decomposition, applying a dual-tree complex wavelet method, or other methods of the sort. Gabor filters, steerable pyramids and other decompositions of the sort may also be applied to produce similar coefficients. Whatever method of decomposition is chosen, the result is a collection of coefficients that are proportional to the magnitude of the variation corresponding to a particular basis function at a particular position on the image.
  • the wavelet coefficients may be compared to the coefficients expected for genuine samples. If the comparison shows that the results are sufficiently close, the sample is deemed authentic. Otherwise, the sample is determined to be a spoof, hi a similar manner, the coefficients may also be used for biometric verification by comparing the currently measured set of coefficients to a previously recorded set from the reputedly same person.
  • a biometric sensor may be operated by a computational system to implement biometric functionality.
  • Fig. 10 broadly illustrates how individual system elements may be implemented in a separated or more integrated manner.
  • the computational device 1000 is shown comprised of hardware elements that are electrically coupled via bus 1026, which is also coupled with the biometric sensor 1056.
  • the hardware elements include a processor 1002, an input device 1004, an output device 1006, a storage device 1008, a computer-readable storage media reader 1010a, a communications system 1014, a processing acceleration unit 1016 such as a DSP or special-purpose processor, and a memory 1018.
  • the computer-readable storage media reader 1010a is further connected to a computer-readable storage medium 1010b, the combination comprehensively representing remote, local, fixed, and/or removable storage devices plus storage media for temporarily and/or more permanently containing computer-readable information.
  • the communications system 1014 may comprise a wired, wireless, modem, and/or other type of interfacing connection and permits data to be exchanged with external devices.
  • the computational device 1000 also comprises software elements, shown as being currently located within working memory 1020, including an operating system 1024 and other code 1022, such as a program designed to implement methods of the invention. It will be apparent to those skilled in the art that substantial variations may be used in accordance with specific requirements. For example, customized hardware might also be used and/or particular elements might be implemented in hardware, software (including portable software, such as applets), or both. Further, connection to other computing devices such as network input/output devices may be employed
  • a purported skin site is illuminated as indicated at block 1104 with white light. This permits the biometric sensor to receive light from the purported skin site at block 1108. As described above, the received light may be analyzed in a number of different ways in implementing a biometric function.
  • the flow diagram shows how certain combinations of analyses may be used in implementing the biometric function, although it is not necessary that all steps be performed. In other instances, a subset of the steps may be performed, additional steps might be performed, and/or the indicated steps might be performed in a different order than indicated.
  • a liveness check may be performed with the received light to confirm that the purported skin site is not some type of spoof, usually by verifying that it has the characteristics of living tissue. If a spoof is detected, an alert may be issued at block 1164.
  • the specific type of alert that is issued may depend on the environment in which the biometric sensor is deployed, with audible or visual alerts sometimes being issued near the sensor itself; in other instances, silent alerts may be transmitted to security or law- enforcement personnel.
  • the light received scattered from the purported skin site may be used at block
  • the purported skin site is a volar surface of a finger
  • a surface image will include a representation of the pattern of ridges and valleys on the finger, permitting it to be compared with a database of conventional fingerprints at block 1124.
  • the received light may be used to derive a spatio-spectral image at block 1128.
  • This image may be compared with a spatio-spectral database having images that are associated with individuals at block 1132. In either instance, the comparison may permit the individual to be identified at block 1136 as a result of the comparison.
  • the spatio-spectral data includes still additional information that may provide greater confidence in the identification, whether the identification is made by comparison with a conventional fingerprint database or through comparison with spatio-spectral information. For example, as indicated at block 1140, demographic and/or anthropometric characteristics may be estimated from the received light. When the database entry matched to the image at block 1136 includes demographic or anthropometric information, a consistency check may be performed at block 1144. For instance, an individual presenting himself may be identified as a white male having an age of 20 - 35 years from the estimated demographic and anthropometric characteristics.
  • the database entry against which the image is matched identifies the individual as a 68-year-old black woman, there is a clear inconsistency that would trigger the issuance of an alarm at block 1164.
  • Other information may also be determined from the received light, such as an analyte concentration at block 1156. Different actions may sometimes be taken in accordance with the determined analyte level. For example, ignition of an automobile might be prohibited if a blood-alcohol level exceeds some threshold, or an alarm might be issued if a blood-glucose level of a medical patient exceeds some threshold. Other physiological parameters, such as skin dryness conditions and the like, may be estimated in other applications, with still other actions sometimes being taken in response.
  • Fig. 12 provides a similar flow diagram to illustrate applications of a texture biometric sensor.
  • the sensor is used by positioning a skin site of an individual in contact with the detector at block 1204.
  • the detector may be relatively small so that only a portion of a finger surface is positioned in contact with the detector; because of the nature of texture biometrics, variations in the specific portion of the surface placed in contact during different measurements are not detrimental.
  • Data are collected by illuminating the skin site at block 1208 and receiving light scattered from the skin site with the detector at block 1212.
  • the flow diagram indicates that different types of analyses may be performed.
  • One category of analysis uses purely spectral comparisons of information.
  • Another category of analysis indicated generally at blocks 1220 andl228 uses image texture information by determining the image texture from spatio-spectral information in the received light at block 1220 and comparing that image texture with a database of texture biometric information at block 1228. With either or both types of analysis, a biometric function is performed, such as identification of the individual at block 1232.

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Abstract

La présente invention concerne des procédés et des systèmes permettant de réaliser une fonction biométrique. Un site cutané désigné d'un individu est éclairé à l'aide d'une lumière d'éclairage. Le site cutané désigné est en contact avec une surface. La lumière diffusée provenant du site cutané désigné est reçue dans un plan qui inclut la surface. Une image est formée à partir de la lumière reçue. Une mesure de texture d'image est générée à partir de l'image. La mesure de texture d'image générée est analysée pour réaliser la fonction biométrique.
EP07873944A 2006-07-19 2007-07-19 Capteurs biométriques spectraux Ceased EP2041697A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US11/458,607 US7751594B2 (en) 2003-04-04 2006-07-19 White-light spectral biometric sensors
US11/458,619 US7545963B2 (en) 2003-04-04 2006-07-19 Texture-biometrics sensor
PCT/US2007/073886 WO2008111994A1 (fr) 2006-07-19 2007-07-19 Capteurs biométriques spectraux

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EP2041697A1 true EP2041697A1 (fr) 2009-04-01
EP2041697A4 EP2041697A4 (fr) 2012-09-19

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KR101433882B1 (ko) 2014-09-22
CN101529445B (zh) 2014-04-30
JP2009511094A (ja) 2009-03-19
KR101489757B1 (ko) 2015-02-04
EP2041697A4 (fr) 2012-09-19
IL189797A (en) 2014-11-30
JP2009544106A (ja) 2009-12-10
IL196253A0 (en) 2009-09-22
IL196253A (en) 2014-11-30
KR20090040436A (ko) 2009-04-24
IL189797A0 (en) 2008-11-03
WO2008111994A1 (fr) 2008-09-18
CN101529445A (zh) 2009-09-09
KR20080050460A (ko) 2008-06-05

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