Abstract:
A system and method for authenticating a user of a device. A multi-band biometric iris scan camera system is capable of obtaining an iris image using near-infrared (NIR) light and/or visible wavelength (VW) light. The camera system can initially image a user to detect the iris color of the user and, based on the iris color, determine whether to use the NIR iris scan or the VW iris scan. Additionally, NIR and VW systems can be operated as integrated camera systems. The iris scan camera system can take a series of images and compare against a database of anonymous iris images captured at different illumination conditions, for selecting a preferred illumination condition for capturing the iris and performing authentication. The iris scan camera system can optionally track eye movement to determine when to trigger an iris scan, identify obstructions to the iris such as eyelids and eyelashes to implement corrective measures in the iris image processing, and identify facial features to determine whether the left and/or right eye is being imaged.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application Ser. No. 61/943,104, filed Feb. 21, 2014, entitled “Biometric Iris Scan Method and Apparatus,” the entire content of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     Embodiments of the present disclosure generally relate to identifying a user of a device. More specifically, embodiments of the present disclosure relate to authenticating a user of a host device via iris identification. 
     BACKGROUND 
     Many electronic devices, such as smart phones and tablets, integrate biometric devices for the purpose of user authentication. The biometric devices can include, for example, iris scanners and camera systems capable of supporting iris identification functions, as well as additional functions such as facial recognition and gesture or motion recognition. However, iris scan systems have a number of limitations, especially those related to user variability, for example variability in iris color for several users of the device. Iris color is a result of differential absorption of light incident on pigmented cells in the outermost layer of the iris. A lesser amount of pigmentation results in less absorption and more light being reflected from the inner layers of the iris. Scattering during transmission of reflected light through the outer layer dictates perceived iris color, for example, a blue iris appearance. Higher levels of pigmentation lead to progressively darker iris coloring, with a dark brown iris appearance occurring at the upper end of high pigmentation levels. 
     An iris scan system optimized for one type of iris (e.g., iris color) can have limited functionality for a different type of iris, for example, optimization for a blue iris can limit capability for recognition of a brown iris. This can result in the iris scan system failing to correctly identify a user of the device. 
     Presently there are many variations of iris scan camera systems that function to capture images of the iris. Biometric iris scan camera systems that can be implemented on a mobile device face a number of challenges for effective operation. Several of these challenges include: iris variability (e.g. a user can have an iris color that is brown, blue, green, or another color); iris obstructions (e.g. eyelids, eyelashes, and other inherent features of the user can interfere with obtaining an image of the iris); ambient illumination (e.g. operation in full sunlight or in the presence of a strong optical noise source); motion blur (e.g. caused by eye saccades or other motions either controlled or involuntary); depth of field at close distances (e.g. images obtained at less than the camera systems intended focal length); additional cost and additional space for a biometric iris scan system, and; limited field of view. For reliable identification the camera must capture an image with resolution compatible with, for example, an approximately 200-row by 200-column line scan of the iris. The iris is typically only 10-12 mm in diameter, while the distance between the camera and the iris is considerable, typically approximately 40-50 cm; therefore, the camera capture area must be properly positioned on the face and iris area. A biometric iris scan camera system that is capable of addressing these issues would be advantageous. 
     SUMMARY 
     According to embodiments of the present disclosure, a host device includes a biometric iris scan camera system for reliable iris identification and user authentication. The iris scan camera system is capable of obtaining an iris image using near-infrared (NIR) light and/or visible wavelength (VW) light. The camera system can initially image a user to detect the iris color of the user and, based on the iris color, determine whether to use the NIR iris scan or the VW iris scan. Additionally, NIR and VW systems can be operated as integrated camera systems. The iris scan camera system can take a series of images and compare against a database of anonymous iris images captured at different illumination conditions, for selecting a preferred illumination condition for capturing the iris and performing authentication. The iris scan camera system can optionally track eye movement to determine when to trigger an iris scan, identify obstructions to the iris such as eyelids and eyelashes to implement corrective measures in the iris image processing, and identify facial features to determine whether the left and/or right eye is being imaged. 
     According to an aspect of the present disclosure, a biometric iris scan camera system for a host device includes a first illumination source disposed on a host device and configured to illuminate a person at a near infrared (NIR) wavelength during an image capture. The host device includes a second illumination source disposed on the host device and configured to illuminate the person at a visible wavelength (VW), and a biometric camera disposed on the host device. The biometric camera includes a first imaging sensor configured to convert an NIR image of the person into an electronic signal for generating a first video image of the person, a second imaging sensor configured to convert a VW image of the person into an electronic signal for generating a second video image of the person, and a processor configured to select, based on an iris color of the user, one of the first illumination source and the second illumination source to illuminate the person during the image capture, to receive a corresponding video image of the person, and to determine an authentication status of the person based on the video image. 
     According to another aspect of the present disclosure, a method of capturing an image of a person for biometric identification includes selecting an illumination wavelength based on an iris color of a person. The method includes illuminating the person with a light source at the selected wavelength during an image capture, the light source adjacent to a camera system comprising a first image sensor responsive to a near infrared (NIR) wavelength and a second image sensor responsive to a visible wavelength (VW), the camera system and the light source housed in a host device. The method includes receiving reflected illumination of the person at the selected wavelength during the image capture, at the image sensor corresponding to the selected wavelength. The method includes generating an electrical signal corresponding to the reflected illumination of the person, processing the electrical signal to generate an image of the iris of the person, and determining an authentication status of the person based on the iris image. 
     According to another aspect of the present disclosure, a mobile apparatus operable for biometric user authentication includes a processor, a memory storing an iris database and operatively coupled to the processor, an illumination source configured to emit illumination at a controlled wavelength, the illumination operable for illuminating an iris of a subject, and a camera. The camera includes a first imaging sensor configured to convert a near-infrared (NIR) image of the subject into an electronic signal for generating a first video image of the iris, and a second imaging sensor configured to convert a visible wavelength (VW) image of the person into an electronic signal for generating a second video image of the iris. The processor is configured to select the controlled wavelength for an image capture based on an iris color, and to receive and match video images of the iris with a previously registered image stored in the iris database, wherein the subject is authenticated if a match is determined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention: 
         FIG. 1  is a block diagram illustrating a biometric iris scan camera system on a host device, according to an embodiment of the present disclosure. 
         FIG. 2  is a flow chart illustrating a method of operation of a biometric iris scan camera system on a host device, according to an exemplary embodiment of the present disclosure. 
         FIG. 3  is a flow chart illustrating a method of operating a biometric iris scan camera system to determine an imaging capture mode, according to an exemplary embodiment of the present disclosure. 
         FIG. 4  is a flow chart illustrating a method for iris image acquisition and processing for purposes of user recognition and authentication, including calibration steps for optimization of illumination conditions and implementation in the context of an anonymity protocol, according to an exemplary embodiment of the present disclosure. 
         FIG. 5  is a schematic diagram illustrating a visible wavelength image sensor featuring narrow band pixels for use in a biometric iris scan camera system on a host device, according to exemplary embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to several embodiments. While the subject matter will be described in conjunction with the alternative embodiments, it will be understood that they are not intended to limit the claimed subject matter to these embodiments. On the contrary, the claimed subject matter is intended to cover alternative, modifications, and equivalents, which can be included within the spirit and scope of the claimed subject matter as defined by the appended claims. 
     Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. However, it will be recognized by one skilled in the art that embodiments can be practiced without these specific details or with equivalents thereof. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects and features of the subject matter. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. 
     The term “component” or “module”, as used herein, means, but is not limited to, a software or hardware component, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), which performs certain tasks. A component or module can advantageously be configured to reside in the addressable storage medium and configured to execute on one or more processors. Thus, a component or module can include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functionality provided for the components and components or modules can be combined into fewer components and components or modules or further separated into additional components and components or modules. 
     Some portions of the detailed description are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits that can be performed on computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. A procedure, computer-executed step, logic block, process, etc., is here, and generally, conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout, discussions utilizing terms such as “accessing,” “writing,” “including,” “storing,” “transmitting,” “traversing,” “associating,” “identifying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     Referring now to  FIG. 1 , a block diagram is depicted illustrating an exemplary embodiment of a biometric iris scan camera system on a host device  100 . The device  100  has components including a memory  112 , at least one processor  114 , input output devices (I/O)  116 . According to an exemplary embodiment, the host device  100  is provided with a biometric iris scan camera system. The biometric iris scan camera system can be used, for example, to capture images of the human iris for user identification and authentication. In one embodiment, the biometric iris scan camera system can include a visible wavelength (VW) imaging sensor  122 , and near infrared (NIR) imaging sensor  126 , a NIR light source  124 , and a VW light source  128 . The VW imaging sensor  122  is sensitive to illumination in the visible spectrum, while the NIR imaging sensor  126  is sensitive to illumination in the near infrared spectrum. The biometric iris scan camera system includes an iris recognition component  118  and an iris database  120 . In one embodiment, the iris recognition component  118  and the iris database  120  are software components stored in the memory  112  and executed by the processor  114 . 
     The biometric iris scan camera system can be used to capture images of a user&#39;s iris for user identification and authentication. The use of the NIR light source  124  and imaging sensor  126  is preferred for imaging a user iris of a darker color (e.g., a brown iris), while use of the VW light source  128  and imaging sensor  122  is preferred for imaging a user iris of a lighter color (e.g., a blue iris). According to an embodiment, in operation the NIR light source  124  illuminates (e.g., flashes) a user of the device with near infrared light during image capture, and an imaging sensor sensitive to NIR wavelengths (e.g., NIR imaging sensor  126 ) converts an optical image of an object into an electronic signal for image processing. According to embodiments of the present disclosure, the biometric camera system can also include a visible wavelength (VW) light source  128  that illuminates a user of the device with visible light during image capture, and an imaging sensor sensitive to visible wavelengths (e.g., VW imaging sensor  122 ) that converts an optical image of an object into an electronic signal for image processing. Video images output from the imaging sensor (e.g., NIR imaging sensor  126 , VW imaging sensor  122 , or a combination thereof) are received by the iris recognition component  118 , which determines an authentication status of the user. For example, the authentication status of the user is determined via attempts to match the image of the iris with previously registered images stored in the iris database  120 . If a match is found, then the user is able to be authenticated. 
     The memory  112 , the processor  114 , the I/O  116 , the VW imaging sensor  122 , the NIR imaging sensor  126 , and the display  110  can be coupled together via one or more system buses (not shown). The memory  112  can comprise one or more memories comprising different memory types, including RAM, ROM, cache, virtual memory and flash memory, for example. The processor  114  can include a single processor having one or more cores, or multiple processors having one or more cores. The I/O  116  is a collection of components that input information and output information. Example components comprising the I/O  116  can include a microphone, speaker, and a wireless network interface controller (or similar component) for communication over the network. The processor  114  can execute an operating system (OS) that manages hardware resources and performs basic tasks. Examples of the OS can include Symbian™, BlackBerry OS™, iOS™, Windows™, and Android™. In one embodiment, the display  110  can be integrated with the host device  100 , while in another embodiment the display  110  can be external to the host device  100 . 
     In one embodiment, the host device  100  can comprise any type of mobile device form factor, including but not limited to: a cell- or smart-phone; a tablet; a notebook or laptop computer; a television; and a wearable computer, for example. In one embodiment, the host device  100  can be implemented with the display  110 , the VW imaging sensor  122 , and NIR imaging sensor  126  located on the same side of the host device  100 , such that the VW imaging sensor  122  and NIR imaging sensor  126  are pointed at a user as the user holds the device to view the display  110 . In the embodiment where the host device  100  comprises a laptop or notebook, the VW imaging sensor  122  and NIR imaging sensor  126  are typically housed within a lid of the laptop. 
     As shown in  FIG. 1 , in an embodiment the VW imaging sensor  122  and NIR imaging sensor  126  are located in one corner of the host device  100  (although other locations are possible), while the NIR light source  124  and VW light source  128  can be located in opposite corners, to offset the NIR light source  124  and VW light source  128  from the VW imaging sensor  122  and NIR imaging sensor  126  within the body of the host device  100 . The biometric iris scan camera is configured to capture iris images at distances typically of around 40-50 cm. The resolution of the captured iris image is configured to be high enough to support an adequate number of points scanned upon the iris image to identify a user, typically such a resolution corresponding to a 200-row by 200-column line scan. Focal length and field of view of the camera system are adjusted accordingly so that sufficient resolution is achieved. 
     In an embodiment of the present disclosure, the NIR light source  124  can be implemented using micro light emitting diodes (LEDs), a laser diode, or another light source with emission in the infrared band (i.e. 700-900 nm wavelength). The emission can be either narrow- or broad band within this infrared spectrum. According to an embodiment, the NIR light source  124  can be focused and directed to point into a user&#39;s eye located at an expected distance when the host device  100  is held normally by the user. 
     In some embodiments, the VW light source  128  can be one of a white light LED, a blue light LED, or an LED of a different color in the visible band. The VW light source  128  can be focused and directed to point into the user&#39;s eye located at an expected distance when the host device  100  is held normally by the user. According to an embodiment, the VW light source  128  is optional, and sunlight and/or other ambient light sources can be used in place of the VW light source  128 . According to an embodiment, detected obstructions (such as eyelashes) that interfere substantially with iris image acquisition can trigger use of VW light source  128  (e.g., an LED) instead of an ambient light source (such as sunlight). In another embodiment the VW image sensor  122  used for VW iris scanning can be a standard red-green-blue (RGB) image sensor used for conventional image acquisition, such as those found on host devices including smart phones, tablets, and laptop computers. For example, the VW image sensor  122  can be a front facing camera such as one typically found on a mobile device for video chatting purposes. 
     In one embodiment, the VW imaging sensor  122  and NIR imaging sensor  126  can include a built-in rolling shutter or a freeze-frame shutter. In one embodiment, the VW imaging sensor  122  and NIR imaging sensor  126  can comprise a digital charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS), and can possess a pixel size and pitch adequate to capture sufficient points in the iris image for authentication purposes. The required pixel size and pitch are a function of the field of view, focal length, and other optical considerations. In one embodiment, the NIR light source  124  emits light at a power level below 1 mW and near a wavelength of 850 nm. In another embodiment the NIR light source  124  emits light at a power level substantially above 1 mW, possibly up to several tens or hundreds of mW or more. Different combinations of energy and time can be selected in order to optimize different imaging scenarios as desired, with variable NIR light source  124  power levels. 
     In one embodiment, the VW light source  128  emits light at a power level up to 10 mW and at a wavelength within the range 390-700 nm. In another embodiment the VW light source  128  emits light at a power level substantially above 10 mW, up to several hundred mW or more. Different combinations of energy and time can be selected in order to optimize different imaging scenarios as desired, with variable VW light source  128  power levels. As an example, for a VW light source  128  configured to output 10-100 mJ of energy with a short pulse duration, such as 1-10 μs, the power level can reach 1000-100,000 W. 
     Iris Recognition 
     Recognition of the iris via iris recognition  118  includes distinguishing the iris from the sclera and the pupil. This can be accomplished, for example, by identifying high contrast edges of an iris image to be the boundary between these portions of the eye. Taking the derivative of the image intensity and identifying local extrema of the derivative&#39;s magnitude can determine the transitions from sclera to iris, and from iris to pupil. Obstructions, such as eyelids and eyelashes, can be excluded using approaches such as feature recognition and geometric modeling for identification of the obstructions. Pattern matching of a captured iris image for purposes of identification and authentication involves: aligning the captured iris image with an iris image from a database iris image entry (e.g., iris database  120 ); choosing an appropriate representation of the iris image so the distinctive aspects of the iris pattern are apparent; evaluating the quality of match between the captured iris image and the database entry; and, making a determination as to whether or not the captured iris image matches a database entry. 
     Referring now to  FIG. 2 , a process  200  is depicted for iris image processing for purposes of user identification and authentication. The flow chart  200  can be implemented as computer-executable instructions residing on some form of non-transitory computer-readable storage medium. 
     At step  202  a determination is made of the iris color of a user, via an image of the user. According to an embodiment the image of the user is taken in real-time, that is, just prior to the determination of the iris color. For purposes of user identification and authentication there are generally four classes of iris colors: dark brown; light brown; blue; and, blue-green. The Illumination light source wavelength for preferred imaging of each of these iris color types is different. Illumination centered about the NIR wavelengths is generally preferred for dark brown irises, while illumination centered about the NIR-red wavelengths is generally preferred for light brown irises. Illumination centered about blue wavelengths is generally preferred for blue and blue-green irises. 
     At step  204  an iris image capture mode is selected, based upon the iris color determined at step  202 . According to an embodiment, the capture mode determines the components of the biometric iris scan camera system that are used for determining an authentication status of the user. For example, the use of the NIR light source  124  and imaging sensor  126  is preferred for imaging a user iris of a darker color (e.g., a brown iris), while use of the VW light source  128  and imaging sensor  122  is preferred for imaging a user iris of a lighter color (e.g., a blue iris). According to embodiments of the present disclosure, the capture mode is exclusive, and either components of the NIR spectrum (e.g., employing NIR light source  124  and imaging sensor  126 ) or the VW spectrum (e.g., employing VW light source  128  and imaging sensor  122 ) are activated. According to some embodiments, the capture mode can include activation of both the VW imaging sensor  122  and the NIR imaging sensor  126 , as well as the NIR light source  124 . According to some embodiments, activation of the VW light source  128  is optional. 
     At step  206  the user is imaged according to the capture mode selected at step  204 . Image capture includes activation of the illumination source corresponding to the capture mode (e.g., NIR or VW), generation of an image by an imaging sensor responsive to the illumination wavelength, and processing of the image by a camera system processor (e.g., processor  114 ). 
     At step  208  the user is authenticated, based on the image of the iris acquired at step  206 . For example, the authentication status of the user is determined via attempts to match the image of the iris with previously registered images stored in the iris database  120 . If a match is found, then the user is able to be authenticated. The iris image may be pre-processed, for example via isolation of relevant portions of the iris image from the complete image, noise reduction, etc. Further, iris image processing can include a filter application for texture or feature extraction, and quantization of extracted iris image features into a binary vector. The match determination to iris database  120  can be based on a comparison to database iris image feature vectors of iris images in iris database  120 . 
     In one embodiment, processing of the iris image for purposes of iris recognition and authentication at step  208  includes the use of a Gabor filter to extract the features of the iris. The Gabor filter is a form of Fourier transform which functions as a bandpass filter that is readily applicable for edge or feature detection for an image. The response of the Gabor filter is from the multiplication of a Gaussian envelope function (e.g., a window function providing greater weight for a portion of a signal near, for example, a particular time region) with a complex oscillation function (e.g., a complex sinusoid). The Gabor filter applied to an iris image can be defined in various coordinate systems including, for example, a Cartesian coordinate system or a polar coordinate system. The Gabor filter is orientation-sensitive in multiple dimensions. According to embodiments of the present disclosure, the user iris image can further be processed with a set of Gabor filters with different parameter values, such as different bandwidths and different modulation frequencies. Other filtering and feature extraction techniques are consistent with the spirit and scope of the present disclosure. 
     The iris feature vectors extracted from the user iris image, unique to each iris, are quantized for conversion to binary form. From binary form, the Hamming distance can be used as a classifier for comparison between different binary iris feature vectors (e.g., between the user iris and irises of iris database  120 ). Other matching techniques are consistent with the spirit and scope of the present disclosure. Match determination based on comparison of the user iris image feature vector and an iris image feature vector from iris database  120  is able to be performed using the Hamming distance between two iris image feature vectors of equal string length. The Hamming distance functions as a classifier to compare iris features through statistical independence, where the number of corresponding string positions which are different between two iris feature vectors indicate the degree of dissimilarity (e.g., the number of string element substitutions required to generate a match can be minimized in order to determine the closest match). 
     Referring now to  FIG. 3 , a flow chart  300  illustrates a method of determining a band (e.g., illumination spectrum) of light source and imaging sensor operation for a biometric iris scan camera system, according to embodiments of the present disclosure. In general, iris colors of a darker color have a higher contrast value, and are preferably imaged at NIR, while iris colors of a lighter color have a lower contrast value and are preferably imaged at visible wavelengths. The flow chart  300  can be implemented as computer-executable instructions residing on some form of non-transitory computer-readable storage medium. 
     At step  302  a determination is made of a contrast value of an iris image. According to an embodiment the iris image of a user is taken in real-time, that is, just prior to the determination of the iris contrast. The contrast value can be computed by a processor of a host device, for example, processor  114  of host device  100 . 
     At step  304  the contrast value determined at step  302  is compared against a threshold contrast level. According to embodiments of the present disclosure, the threshold contrast level corresponds to an iris color where a transition in image sensor responsiveness occurs. More specifically, the transition can be a transition in responsiveness from NIR wavelengths to VW, such that iris colors of greater contrast levels are imaged with greater responsiveness by an imaging sensor sensitive to NIR wavelengths, and iris colors of contrast levels below the threshold are imaged with greater responsiveness by an imaging sensor sensitive to VW. At step  304  if the contrast value is determined to be above the threshold, the method proceeds to step  306 . Step  306  corresponds to image captures performed at NIR wavelengths, where a NIR illumination source (e.g., NIR illumination source  124 ) is used in concert with an imaging sensor responsive to NIR (e.g., imaging sensor  126 ). 
     If at step  304  it is determined that the iris contrast is not above the threshold level, the method proceeds to step  308 . Step  308  corresponds to image captures performed at visible wavelengths, where visible illumination is used in concert with an imaging sensor responsive to visible wavelengths (e.g., imaging sensor  122 ). According to embodiments of the present disclosure, the level of ambient illumination is determined to see if it is of sufficient illumination for imaging of the iris at visible wavelengths. 
     At step  310  a determination is made of whether ambient light levels are sufficient for imaging at visible wavelengths. If YES, the method proceeds to step  312 , where ambient light is used in concert with a visible wavelengths imaging sensor to capture an image of the user iris. 
     If NO, ambient light is not sufficient for imaging and the method proceeds to step  314 . Step  314  includes the use of a visible wavelength illumination source (e.g., VW illumination source  128 ) in concert with a visible wavelengths imaging sensor to capture an image of the user iris. 
     Illumination Conditions 
     According to embodiments of the present disclosure, an optional step of process  200  described above includes a calibration step incorporating use of different lighting conditions prior to the image acquisition step  204 . Referring now to  FIG. 4 , a flow chart  400  illustrates a method of iris image acquisition and processing for purposes of user recognition and authentication, including calibration steps for optimization of illumination conditions, and optional implementation in the context of an anonymity protocol. The flow chart  400  can be implemented as computer-executable instructions residing on some form of non-transitory computer-readable storage medium. 
     Step  402  of process  400  can be performed during step  202  of process  200 , determination of an iris color of a user. At step  402  a series of iris images corresponding to a series of lighting conditions are captured. According to an embodiment the series of images are captured in real-time, that is, just prior to the authentication of the user. 
     At step  404  a database of anonymous irises that have been imaged under different illumination conditions is accessed. Iris images captured at an earlier time and provided as part of the iris image database can include a series of iris image datasets, each dataset corresponding to a different lighting condition. According to an embodiment, generation of such a database for use in iris-based user recognition and authentication (e.g., process  200 ) may be incorporated as a step ahead of those related to real-time iris image acquisition. 
     At step  406  a match determination is performed to select preferred illumination conditions for imaging an iris of a user for authentication. According to an embodiment, the database of iris images is used to provide models against which real-time iris images captured under different lighting conditions can be matched, in order to determine preferred illumination and image acquisition/processing conditions. For example, each entry in the database can represent a specific iris type (e.g., color), where the image of that iris type is captured using known, preferred conditions. That is, for a brown iris, the brown iris image in the iris database will have been captured using NIR wavelengths and NIR imaging sensor, at a given illumination source power, exposure time, and further imaging parameter values. By matching the real-time iris images taken under different lighting conditions to database models, the preferred illumination condition and parameter space used to perform recognition and authentication is able to be determined. 
     According to some embodiments of the present disclosure the illumination source is integral to the iris image camera system (e.g., illumination sources  124  and  128  of host device  100 ). However, according to some embodiments other light sources may be used including, for example, ambient light (such as sunlight). For illumination sources originating from the ambient environment, the parameter space of the preferred illumination conditions for the iris image database can take into consideration a different lighting condition for improved imaging results. Additional lighting conditions can include the various illumination sources described above (e.g., illumination sources  124  and  128  of host device  100 ), including the presence of environmental factors affecting the captured iris image. Environmental factors can include, but are not limited to, interference from ambient light, motion blur, image obstructions, and so forth. 
     Anonymity Protocol 
     In certain embodiments, the method  400  described above can be implemented within the context of an anonymity protocol, such that no record of traceability between iris data and individuals exists. A method of iris image processing for purposes of untraceable user identification and authentication comprises the steps of: generation of an anonymous iris database (e.g., using iris contrast as described herein); downloading the database model to a host device; acquiring a set of images of the user&#39;s iris under different lighting conditions; performing weighted optimization of uniqueness (e.g. based on the Hamming distance response to the database values); using the image from the set of images of the user&#39;s iris determined to be the most ideal in terms of illumination conditions and parameter space for recognition and authentication. 
     The anonymous iris database according to an exemplary embodiment includes around 10,000 iris images of different iris types (e.g., different iris colors) taken under different lighting and processing conditions and parameters. The iris images can include approximately equal numbers of images for each iris type (e.g., approximately 2500 images of brown irises, 2500 images of blue irises, etc.). According to embodiments of the present disclosure, each of the supplied iris images in the database contains no link to the person from which the iris image originates. According to an embodiment, the database can be stored locally on a host device so that utilization of the database during user recognition and authentication need not require transmission of any data beyond the host device (e.g. to a shared or externally controlled data center). According to an embodiment, the database is stored remotely, and can be accessed via a remote protocol (e.g., the Internet, WiFi, etc.). Real-time images of the user&#39;s iris may be retained locally for recognition and authentication, without transmission of any related data outside the host device. 
     Combined Near-Infrared and Visible Wavelength Functionality 
     While embodiments of the NIR and VW iris scan functions have been described as image captures of NIR and VW occurring in sequence, iris image capture using the NIR and VW camera systems simultaneously is also within the spirit and scope of the present invention. In one embodiment, the NIR and VW illumination sources (e.g., illumination sources  124  and  128 , respectively) can emit light at the same time, and separate NIR and VW image sensors (e.g., imaging sensors  126  and  122 , respectively) can be exposed at the same time. According to another embodiment, NIR and VW image sensors are integrated into a single NIR/VW image sensor. Once iris images are acquired by both the NIR and VW imaging sensors, the iris image deemed to be of higher quality for purposes of user identification and authentication can be used for authentication purposes, while the iris image determined to be of lower quality can be rejected. Higher quality may be determined using measures such as higher contrast or MTF of the iris images. 
     Ambient Light Rejection 
     Ambient light presents a difficulty for capturing an image of the user (e.g., an iris) with adequate detail to perform an image match with pre-registered images. Ambient light can saturate an imaging sensor and overwhelm the signal (that is, the reflected illumination from the user, such as the iris). One approach to minimizing ambient noise is to make the exposure time to be as short as practically possible. 
     In one embodiment, a solid-state shutter comprising gallium arsenide (GaAs) may be used with either the NIR or VW imaging sensor, or both. Such a shutter can change its state from opaque to transparent in a very short time (e.g. several nanoseconds) by an externally applied voltage. In an embodiment, a GaAs shutter is used to image an iris with light near a wavelength of 850 nm. 
     In an embodiment, when performing an iris scan in the visible light spectrum, light source flash duration is minimized (in a case where VW illumination source  128  is used), and thereby exposure time is reduced accordingly. In an embodiment, the flash duration of VW light source  128  is below 150 ms and the power is in the range of 10 mW, to compensate for the short exposure time. The instantaneous light source power can be made as high as practically possible while still preventing damage to the human eye or causing any user discomfort. Additional measures can be taken to avoid the light source causing user discomfort, for example the use of a diffuse light source. According to an embodiment, keeping a solid-state shutter (e.g., GaAs shutter) closed at all times except during image capture reduces the ambient light received from elsewhere in the scene significantly. 
     Adverse ambient light effects can also be reduced by the use an imaging sensor with narrow band pixels, where the bandwidth of the pixels is matched to the emission wavelengths of the light source. Referring now to  FIG. 5 , an imaging sensor  500  featuring narrow band pixels  505  for use in a biometric iris scan camera system is depicted. According to an embodiment, the imaging sensor  500  is a visible wavelength image sensor. According to an embodiment the image sensor  500  includes red, green, and blue pixels. As a non-limiting example, for a blue light LED used as the light source, pixel bandwidth for narrow band pixels  505  can be configured around a narrow range corresponding to blue light (e.g., for blue LED, range about 450-495 nm). Other light source wavelengths and narrow band pixels are consistent with the spirit and scope of the present disclosure. According to embodiments of the present disclosure, narrow band pixels  505  may be arranged in a Bayer pattern in a manner similar to conventional RGB pixel arrays. According to some embodiments, narrow band pixels  505  can make up only a subset of the pixels within a pixel array, and are integrated into the pixel array that also contains conventional bandwidth pixels. Narrow band pixels  505  can comprise one or more of red, green, and blue pixels, and combinations thereof. 
     In addition to rejection of ambient illumination, embodiments of the present disclosure include a host device configured for very short exposure time, reducing motion blur during image capture. According to some embodiments, the NIR and VW sensing functions can be integrated onto a single image sensor capable of detecting both VW and NIR light. Such an integrated image sensor can include various combinations of conventional bandwidth NIR pixels, conventional bandwidth VW pixels, and narrow band pixels centered about any desired wavelength corresponding to those used for iris scanning. These pixels can be arranged in various patterns, including those featuring a Bayer pattern. 
     A method and system for a biometric iris scan camera system has been disclosed. The present invention has been described in accordance with the embodiments shown, and there could be variations to the embodiments, and any variations would be within the spirit and scope of the present invention. Aspects of the present disclosure can be embodied in a computer-readable media including program instructions to implement various operations embodied by a computer or computing device (e.g., a cellular phone, tablet device, etc.). The media can also include, alone or in combination with the program instructions, data files, data structures, and the like. The media and program instructions can be those specially designed and constructed for the purposes of the example embodiments of the present disclosure, or they can be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media, for example, CD ROM disks and DVD, magneto-optical media, for example, optical disks, and hardware devices that can be specially configured to store and perform program instructions, for example, read-only memory (ROM), random access memory (RAM), flash memory, and the like. Aspects of the present disclosure can also be realized as a data signal embodied in a carrier wave and comprising a program readable by a computer and transmittable over the Internet. Examples of program instructions include both machine code, for example, produced by a compiler, and files containing higher level code that can be executed by the computer using an interpreter. The described hardware devices can be configured to act as one or more software modules in order to perform the operations of the above-described example embodiments of the present disclosure. 
     Embodiments of the present disclosure are thus described. While the present disclosure has been described in particular embodiments, it should be appreciated that the present disclosure should not be construed as limited by such embodiments, but rather construed according to the following claims. Accordingly, many modifications can be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.