Abstract:
Low-cost, easy-to-use alignment target generators for aligning a user&#39;s own face or eye to a camera or scanner are based on field-of-view visual feedback from a filtered or apertured planar light source. These approaches may be made agnostic to the scanner&#39;s operating system or other software. Alternatively, software on the scanner or its host device may create a solid light-colored section of an existing display screen to use as a planar light source. In some embodiments, the planar light source may be the virtual image of an object viewed in a plane mirror.

Description:
FIELD 
       [0001]    Related fields include biometrics, and more particularly facial scanning and recognition. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0002]      FIG. 1  is a flowchart of an example of a process for iris scanning 
           [0003]      FIGS. 2A-D  represent examples of iris vignetting 
           [0004]      FIGS. 3A-G  are conceptual illustrations of examples of planar light sources. 
           [0005]      FIGS. 4A-H  conceptually illustrate examples of beam-shaping elements that may be used in some embodiments of alignment target generators 
           [0006]      FIGS. 5A-B  conceptually illustrate examples of an annular aperture and an alignment target generator including an annular aperture. 
           [0007]      FIGS. 6A-C  conceptually illustrate examples of an alignment target generator including one or more color filters that change the color of the planar light source depending on the position and angle of the eye 
           [0008]      FIGS. 7A-B  conceptually illustrate examples of an alignment target generator including a beam blocker pierced by two or more converging waveguides. 
           [0009]      FIG. 8  conceptually illustrates a tilted-mirror alignment target generator. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Biometric methods of identification are presently of increasing interest to thwart and deter fraud and identity theft and to make personal portable electronics less valuable to property thieves. Of the desirable properties of an identification biometric trait, iris scanning scores very high in uniqueness, universality, permanence, performance, and (difficulty of) circumvention, and in the midrange of collectability and acceptability. Iris scanning can be sensitive to inconsistencies in distance or angle between the scanner and the user&#39;s body. Vignetting, where part of the object being measured is blocked by the apertures in the scanner or by external objects, may be an especially troublesome source of false errors. This sensitivity, and the resulting “stand very still and stare” requirement placed on users. may be a contributing factor keeping the acceptability score low. 
         [0011]    For purposes herein, the following terms shall have the following meanings: 
         [0012]    “User”: A person being identified by a biometric device. One who uses the biometric device to identify others will be called an “operator” for purposes of this document. 
         [0013]    “Planar light source”: may refer to a direct source of light, such as an LED array, or an indirect source, such as an illuminated diffuser or mirror, in which the light exits from a substantially flat surface (e.g., best-fit radius &gt;1 m; rms roughness &lt;1 mm). 
         [0014]    “Scan”: may refer to any method of data capture for biometrics of a user&#39;s eye or face. 
         [0015]    “Optical surface”: a surface prepared (e.g. shaped, polished or patterned) for entry and/or exit of light (e.g., in most lenses and filters, the front and the back but not the edge; in most prisms, two or more of the non-parallel sides but not the two parallel sides). Not all optical surfaces are smooth or regularly patterned; for example, diffusers may have optical surfaces with controlled random roughness. 
         [0016]    “Parent device”: The device that includes the biometric scanner; this may be a dedicated biometric system (e.g., at the door of an employee-only entrance) or a protected device used for other purposes but equipped with a biometric scanner to limit access to itself, A computer or smart-phone, a high-end machine tool, and a household or company safe are non-limiting examples. 
         [0017]      FIG. 1  is a flowchart of an example of a process for iris scanning Other processes may involve more or fewer steps, or some different steps, yet may be equivalents because they may be similarly sensitive to positioning or angle of a user&#39;s eye. 
         [0018]    The process may be started at step  100  by a user pushing a button, touching a screen, scanning a card or tag, or being detected approaching and stopping within a detection zone. Alternatively, an official operator, such as a test proctor or border guard, may start the process after having the user move into the detection zone. 
         [0019]    An image of the user&#39;s iris, or equivalently a stream of data from a spot scan or some other collection of raw data, is captured in step  102 . In some systems, the image (or other raw data) may be pre-processed at step  104 . For example, the pre-processing may include separating colors to create one or more monochromatic images; separating the iris data from measurements of nearby features such as the sclera, pupil, or eyelid; or accessing a spatial-frequency spectrum from a transform such as a fast Fourier transform (FFT) or a circular Hough transform. 
         [0020]    Image segmentation at step  106  often includes edge detection and may use approaches such as gradient amplitude, gamma modification, non-maxima suppression, or hysteresis thresholding. At step  108 , the extracted data sets are normalized to simplify comparison with stored records. At step  112 , the iris&#39;s “signature,” including its most unique features, is encoded. Many, if not most, of the features that distinguish one individual iris from another are capable of being encoded at low or low-middle frequencies. Therefore, high-frequency noise can be removed from the data with little risk. Step  105 , detecting and removing noise, may optionally be done in its various aspects following image capture  102 , pre-processing  104 , segmentation  106 , normalization  108 , or encoding  112 . Noise an iris measurement may result from the presence of the users&#39; eyelashes or blood vessels in the field of measurement, as well as potentially being introduced by imperfections in the equipment and process. 
         [0021]    At step  114 , the encoded signature pattern is compared with stored samples, e.g., by calculating the Hamming distance between the new sample in the stored sample, or by some other suitable algorithm. Finally at step  116 , the comparison calculations yield a “match or no match” result. 
         [0022]    Step  101 , the alignment of the eye to the instrument, continues to be challenging on multiple levels. Including, in the scanner, a dedicated camera just for the pre-scan alignment process may be costly, bulky, or fragile depending on the scanner configuration and its environment of use. Particularly in self-service situations, an affordable, rugged, and easy wait to pre-align the eye before taking the scan has the potential to mitigate users&#39; aversion to complicated or highly constrained processes. 
         [0023]      FIGS. 2A-D  represent examples of iris vignetting. 
         [0024]    The iris in  FIG. 2A  is in its least-vignetted natural position. The eye is fairly centered and its optic axis is substantially parallel to the scanner optic axis, and the head is facing directly toward the scanner. Dotted-line circle  201  marks the outer iris boundary between the iris and the sclera. Similarly, dotted-line circle  203  marks the inner iris boundary between the iris and the pupil. Even in this optimal position, area  204  of the iris is vignetted by the upper eyelid and eyelashes making some of the iris features inaccessible. Area  204  may be enlarged in some instances if the user is wearing mascara, sleepy, or suffering from allergies, conjunctivitis or a similar eye irritation. 
         [0025]    In  FIG. 2B , the iris is still centered in the eye and the optic axis of the eye is still parallel to the optic axis of the scanner, but the eye was off-center in the scanner field when the scan was taken. Area  214  of the iris is vignetted by the upper eyelid and eyelashes. Additionally, area  216  outside the scan border is vignetted by the edge of the image-capture field and therefore not readable. 
         [0026]    In  FIG. 2C , the eye is looking off towards the side and the iris is in the corner of the eye. Area  224  of the iris is vignetted by the upper eyelid and eyelashes. Area  234  of the iris is vignetted by the lower eyelid and eyelashes. Additionally, the iris is distorted by foreshortening due to a non-perpendicular angle between the optic axis of the eye and the optic axis of the scanner. The right edge of the iris is along line  228  rather than  221 , which distorts the aspect ratio of iris features. 
         [0027]    In  FIG. 2D , the eye is looking off straight into the scanner but the head is turned partially away from the scanner, again putting the iris in the corner of the eye. Area  244  of the iris is vignetted by the upper eyelid and eyelashes. Area  254  of the iris is vignetted by the lower eyelid and eyelashes. Foreshortening places the iris edge at line  238  instead of line  231 . 
         [0028]    In  FIGS. 2B, 2C and 2D , misalignment of the eye or head to the scanner results in more missing or distorted iris features than the optimal alignment of  FIG. 2A . If enough distinguishing features are missing or distorted, the odds of a false match or mismatch increase. 
         [0029]      FIGS. 3A-G  are conceptual illustrations of examples of planar light sources. The examples are non-limiting; other types of planar light sources besides these may be used with embodiments of alignment target generators. 
         [0030]      FIG. 3A  is a schematic symbol for a planar light source  302  emitting light  310 . This symbol in later drawings may represent any of the other illustrated planar light sources or any suitable known substitute. 
         [0031]      FIG. 3B  represents a light-emitting diode (LED)  314  powered through conductive prongs  318  and illuminating planar diffuser  316 . LED  314  may emit light in the manner of a point light source, but when its emitted light is scattered by planar diffuser  316 , the front surface of planar diffuser  316  behaves as a planar light source. Although a packaged LED  314  and separately mounted diffuser  316  are illustrated for ease of understanding, any or all of the components may be thin-film components integrated on a chip in some embodiments. Additionally, a reflective diffuser may replace the illustrated transmissive planar diffuser  316  in some embodiments. 
         [0032]      FIG. 3C  represents an LED array  324  powered through conductive prongs  318 . Individual point-source LEDs are placed sufficiently close together that the human eye sees them as a planar (or linear) light source. A packaged LED array  324  is illustrated for ease of understanding, but LED array  324  may alternatively be integrated on a chip with other scanner components in some embodiments. 
         [0033]      FIG. 3D  represents an LED  334  powered through conductive prongs  338  and illuminating light-guide array  336 . LED  334  may behave essentially like a point light source, but when its light is captured and reshaped by light-guide array  336 , the front surface of light-guide array  336  behaves as a planar light source. Light-guide array  336  may be an array of integrated-optics light-guides or a rigid or flexible bundle of optical fibers. Light-guide array  336  may be short or long. The light guides in light-guide array  336  may be step-index, graded-index, single-mode, multimode or reflective tubes. Although a packaged LED  334  and separately mounted light-guide array  336  are illustrated for ease of understanding, any or all of the components may be thin-film components integrated on a chip in some embodiments. 
         [0034]      FIG. 3E  represents an LED  344  powered through conductive prongs  348  and illuminating edge-emitting optical fiber  346 . LED  344  may behave essentially like a point light source, but when its light is captured and reshaped by edge-emitting optical fiber  346 , the front surface of a coil or other planar formation of edge-emitting optical fiber  346  behaves as a planar light source. Although a packaged LED  334  and coupled edge-emitting optical fiber  346  are illustrated for ease of understanding, any or all of the components may be thin-film components integrated on a chip in some embodiments. 
         [0035]    Another alternative family of embodiments may use an existing visible LED on the parent device that can be caused to stay on when the alignment target generator is being used (e.g., “Power On” or “Caps/Num/Fn Lock”). A permanent or removable light-spreading element such as diffuser  316 , light-guide array  336 , or edge-emitting fiber  346  can be positioned in front of the existing LED to form a planar light source. 
         [0036]      FIG. 3F  represents a self-illuminating screen  354 ; for example, based on LEDs or liquid-crystal diodes. Self-illuminating screen  354  is shown as powered through conductive leads  358 . 1  and back electrode  358 . 2 , but may equivalently use a transparent front electrode, or both. Light-emitting layer  354  emits the light from individual pixels or LED illumination divided into pixels. Light-altering layer(s)  356  (polarizers, filters, microlenses, etc.) may be added to change the character of the emitted light. 
         [0037]    Self-illuminating screen  354  may have all its pixels emitting one color, such as white, or may have adjacent pixels emitting different colors for the appearance of a solid mixed color. The resolution may be fairly low and self-illuminating screen  354  will still appear as a planar light source to the user&#39;s eye. 
         [0038]    In some embodiments, self-illuminating screen  354  may be a section of a larger screen, such as a display screen for a smart-phone, tablet computer, or personal computer that authenticates its users through iris recognition. 
         [0039]    In  FIG. 3G , self-illuminating screen  364  is a larger display screen mounted in housing  367 . To perform the iris scan, optics train  366  may be temporarily mounted over part of self-illuminating screen  364  and its housing  367  by removable mounting clip  368 . Removable mounting clip  368  may be held in place by a spring force  369 , by friction between an inner surface of removable mounting clip  368  and an outer surface of housing  367 , or by any other known holding mechanism. After the iris scan authenticates the prospective user, removable mounting clip  368  may be removed, or slid/rotated aside, allowing the entire display screen to be used for other purposes. 
         [0040]    Similarly, a mounting clip may alternatively be used to temporarily mount a beam-spreader and optics train on an existing controllable LED integrated into the housing of the parent device. 
         [0041]      FIGS. 4A-H  conceptually illustrate examples of beam-shaping elements that may be used in some embodiments of alignment target generators. The examples are non-limiting; other types of beam-shaping elements besides these may be used with embodiments of alignment target generators. Additionally, any of the transmissive elements pictured as examples may be replaced by reflective elements that similarly shape an incident light beam. Some embodiments may include negative-powered beam-shaping elements. 
         [0042]      FIG. 4A  is a schematic symbol for a planar light source  302  emitting light  310 . This symbol in later drawings may represent any of the other illustrated planar light sources or any suitable known substitute. 
         [0043]      FIG. 4B  represents a lens  413  with opposing curvatures  413 . 1  and  413 . 2  on two optical surfaces. 
         [0044]      FIG. 4C  represents a lens  423  with one planar optical surface and one curved optical surface. 
         [0045]      FIG. 4D  represents a lens  433  with curves of different radii in the same direction on two optical surfaces. 
         [0046]      FIG. 4E  represents a lens  443  with two elements  443 . 1  and  443 . 2  of different materials, e.g., to achromatize a multi-wavelength beam train, or to otherwise differently shape beams of different wavelengths. 
         [0047]      FIG. 4F  represents a diffractive (Fresnel) lens  453  with amplitude-modulated transmission. 
         [0048]      FIG. 4G  represents a diffractive (Fresnel) lens  463  with phase-modulated transmission. 
         [0049]      FIG. 4H  represents a gradient-index lens  473 , which shapes incoming beams with transverse variations in refractive index rather than (or besides) curved or diffraction-patterned optical input or output surfaces. 
         [0050]      FIGS. 5A-B  conceptually illustrate examples of an annular aperture and an alignment target generator including an annular aperture. 
         [0051]    In  FIG. 5A , beam blocker  504  mounted in housing  505  has a transmissive annular aperture  514  to allow some light to pass through. In the case of a continuous annulus like the one illustrated, the inner and outer parts of beam blocker  504  may be affixed to, or fabricated on, a backplate of material such as glass or plastic that transmits at least some visible light. 
         [0052]    Equivalent designs include segmented annuli formed by a number of unconnected holes or arc-shaped slots, including at least three holes or arc-shaped slots equally spaced around the perimeter of the annulus, forming a ring of dots rather than a solid ring. Because the beam-blocker is one piece in such embodiments, a backplate may not be needed for the purpose of maintaining the structure of beam blocker  504 . 
         [0053]    In  FIG. 5B , a cut-away side view of an alignment target generator, planar light source  502  illuminates beam blocker  504 , optionally through window or diffuser  524 . Window or diffuser  524  may serve as a backplate for beam blocker  504 . Light  510  from planar light source  502  exits the annular space or perimeter holes  514  in beam blocker  504 . Beam-shaping element  503  captures light  510  and shapes it to form an image of annular space or perimeter holes  514  in beam blocker  504 . Aligned eye  511  sees a ring  511 . 1  (or analogous ring of equally sized dots) with uniform width all around its perimeter. Misaligned eye  521  sees a crescent  521 . 1  (or analogous crescent of unequally sized dots). 
         [0054]    If parts of housing  505  do not vignette light  510  exiting the aperture(s) in beam blocker  504 , the alignment sensitivity is determined by the exit angle θ 1 , which depends on the depth d (deeper is more sensitive) and width w (wider is less sensitive) of aperture or hole  514 , and also by imaging angle θ 2 , which depends on the position and focal length of beam-shaping element  503 . Similar relationships apply to some other embodiments. 
         [0055]      FIGS. 6A-C  conceptually illustrate examples of an alignment target generator including one or more color filters that change the color of the planar light source depending on the position and angle of the eye. 
         [0056]    In  FIG. 6A , a side view of an alignment target generator, planar light source  602  illuminates a window with a spectral response that varies across its width. In this figure, line thickness is used as a proxy for color. As illustrated, bottom window section  606  is substantially clear, transmitting light  610  from planar light source  602  essentially unchanged in color. Top window section  616  is a color filter (absorption or reflection) transmitting colored light  620 , a spectral subset of light  610  from planar light source  602 . 
         [0057]    Aligned eye  611  will see a blended spectrum B (i.e., if light  610  is white and light  620  is red, aligned eye  611  will see pink). Misaligned eye  621  will see white (only light  610 ), while misaligned eye  631  will see only red (light  620 ). The alignment target generator of  FIG. 6A  aligns the eye in one plane parallel to the optic axis. 
         [0058]    In  FIGS. 6B and 6C , hatching type is a proxy for color. 
         [0059]      FIG. 6B  is a front view of a 1-D alignment window, showing clear 180-degree sector  606  and color filter 180-degree sector  616 . 
         [0060]      FIG. 6C  is a front view of a 2-D alignment window, showing clear 120-degree sector  606 , first color filter 120-degree sector  616 , and second (different) color filter 120-degree sector  626 . 
         [0061]    Alternatively, a 2-D alignment window may have four 90-degree sectors, each transmitting a different color. In all the described embodiments, the transmission spectra of the different sectors produce unambiguously different colors to the user&#39;s eye. In some embodiments, the transmission spectra may overlap less than 30%. In some embodiments, the peak wavelengths of the transmission spectra may be more than 100 nm apart. 
         [0062]    Note that some embodiments of alignment windows may use a different color filter in place of clear section  606 , so that all the exiting light is altered spectrally in different ways. 
         [0063]      FIGS. 7A-B  conceptually illustrate examples of an alignment target generator including a beam blocker pierced by two or more converging waveguides. 
         [0064]    In  FIG. 7A , a cut-away side view, beam blocker  704  is pierced by waveguides  707 . 1  and  707 . 2 , which capture and transmit light  710  from planar light source  702 . Waveguides  707 . 1  and  707 . 2  may be rigid or flexible. Waveguides  707 . 1  and  707 . 2  may include transmissive core  717  and lower-index cladding  727 . 
         [0065]    Light  710  exits waveguides  707 . 1  and  707 . 2  at a full angle corresponding to the numerical aperture of the waveguides. Additionally, the optic axes of the exiting cones of light converge with each other. Aligned eye  711  is in the smallest spot created by the convergence of the cones. Misaligned eyes  721  are in larger spots; they may still see two dots, but they will be dimmer and perhaps distorted. 
         [0066]    In  FIG. 7B , a front perspective view, four waveguides  707 . 1 - 4 , 90 degrees apart on a circle perimeter, converge to allow alignment in 2 orthogonal axes. 3 waveguides 120 degrees apart would provide non-orthogonal 2-D alignment. In both cases, aligned eye  711  is positioned in the minimum spot for the brightest dots. Scanner input  709  may be located in the center of the circle of waveguide tips. Optionally, beam blocker  704  may be a wall of the parent device&#39;s housing. 
         [0067]      FIG. 8  conceptually illustrates a tilted-mirror alignment target generator. Mirrors  808 . 1  and  808 . 2  are positioned on either side of scanner input  809  and tilted inward toward the scanner input&#39;s optic axis along the perimeter of a cylinder centered on aligned eye  811 . Planar light sources off-axis (not shown) provide illumination to mirrors  808 . 1  and  808 . 2 . 
         [0068]    Aligned eye  811  sees both mirrors  808 . 1  and  808 . 2  because the surfaces of the eye reflect light rays  850 . 1  and  850 . 2  back at normal or near-normal angles to the mirrors. Misaligned eye  821  sees mirror  808 . 1  because the eye reflects ray  850 . 3  along a normal to mirror  808 . 1 . However, misaligned eye  821  does not see mirror  808 . 2  because ray  860 . 1  makes a non-normal angle with mirror  808 . 2  and is reflected as ray  860 . 2  away from the eye. 
         [0069]    In some embodiments of alignment target generators, the planar light source is blocked or powered down before the biometric measurement begins, to avoid excess reflections that may mask features of the iris. 
         [0070]    A 2-D alignment target generator of this type would use at least 3 mirrors arranged around scanner input 809 om the surface of a sphere concentric with the aligned eye position. 
         [0071]    Facial recognition scores high in collectability and acceptability (iris scanning&#39;s weaker areas) as well as universality, in the midrange of uniqueness and permanence, but low in performance and (difficulty of) circumvention. 2-D face recognition is limited in the head positions and angles at which it can measure without losing accuracy. Some of the described alignment techniques for the eye may also help reduce the error margin in face recognition. 
         [0072]    At the same time, remote monitoring of health factors promises to reduce healthcare costs for both patients and healthcare providers. When the nearest doctor&#39;s office is far away and reliable transportation is scarce, or when visits to crowded urban clinics are stressful and pose a risk of contagion, routine post-treatment follow-up may sometimes have practical, as well as financial, advantages. Visual views of a patient&#39;s eyes or face can be helpful for tracking the development of irritations or infections, the healing of wounds and surgical incisions, or other changes in appearance that may indicate changes in underlying health. However, the information value of a set of serial photographs may be limited if the distance, angle, lighting, and other factors vary widely from picture to picture. 
         [0073]    Therefore, the alignment target generators described herein may also be applicable in face recognition and medical communication. 
         [0074]    The preceding Description and accompanying Drawings describe examples of embodiments in some detail to aid understanding. However, the scope of protection may also include equivalents, permutations, and combinations that are not explicitly described herein. Only the claims appended here (along with those of parent, child, or divisional patents, if any) define the limits of the protected intellectual-property rights.