Patent Publication Number: US-8983146-B2

Title: Multimodal ocular biometric system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 13/196,617 filed Aug. 2, 2011, which is a Divisional of U.S. patent application Ser. No. 11/798,500 filed May 14, 2007, which claims priority to U.S. Provisional Application No. 60/800,023 filed May 15, 2006, U.S. Provisional Application No. 60/812,949 filed Jun. 13, 2006, and U.S. Provisional Application No. 60/819,630 filed Jul. 11, 2006, the contents of these applications being incorporated entirely herein by reference. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates generally to instruments for biometric identification, and more particularly, to a multimodal ocular imaging system used for biometric identification. 
     2. Description of the Related Art 
     Due to the unique character of each individual&#39;s retina or iris, various systems attempt to use either the retina or the iris for biometric identification. As such, commercially available ocular imaging systems used for biometric identification generally use a single biometric modality. These imaging systems process images of the iris or the retina from only one of two eyes of a subject. None of these conventional systems processes images of both the iris and the retina in combination. Moreover, these systems do not process images from the iris and/or the retina from both eyes. 
     Conventional single-eye iris imaging systems suffer from several disadvantages. In particular, such systems may suffer from frequent failure to acquire an image, i.e. a high fail-to-acquire (FTA). The effectiveness of these iris imaging systems is often limited by occlusions caused by eyelids and eyelashes, lighting issues (controlled or uncontrolled), focus problems, pupil size variation (between different persons or with the same person), non-linear iris fiber distortion caused by expansion or contraction of the pupil, and rotation and skew of the head or eye. Such systems are also susceptible to spoofing. Moreover, auto focus functions of conventional iris-only systems are affected by scratches in eyeglasses or the reflections from eyeglasses. In fact, ANSI standards require enrollment to be without eyeglasses. Additionally, contact lenses can cause iris outer boundary segmentation problems. Moreover, colored contact lenses can result in spoofing. 
     Conventional single-eye retina imaging systems also have several disadvantages. For instance, problems with such retina imaging systems occur when visible light used for illumination blinds or distracts the user, when the user is not properly aligned with the image capture device, or when poor areas of the retina are chosen for imaging. Furthermore, conventional retina-only systems are also negatively affected by focus problems as well as rotation and skew of the head or eye. 
     SUMMARY OF THE INVENTION 
     Considering the disadvantages of the single modal systems described previously, a need has been identified for a multimodal ocular biometric system that addresses these disadvantages by capturing and combining biometric information from more than one modality. 
     Accordingly, embodiments of the present invention provide a multimodal ocular biometric system that captures and processes images of both the iris and the retina for biometric identification. Biometrics based on a combination of iris and retina data provided by the present invention are more accurate and robust than using biometrics that include data from only the iris or only the retina from a single eye. In addition, such a multimodal system has a lower fail-to-acquire (FTA) than single-eye iris-only or retina-only systems and is less susceptible to spoofing. It is noted that U.S. application Ser. No. 11/087,205, filed on Mar. 25, 2005, describes a Method and System for Generating a Combined Retinal/Iris Pattern Biometric, and is entirely incorporated herein by reference. 
     Thus, in an exemplary embodiment of the present invention, a system for multimodal biometric identification has at least one iris imaging system and at least one retina imaging system. Each iris imaging system has an iris illumination source adapted to emit iris photons to an iris of a right eye or a left eye and an iris image sensor configured to capture an image of the iris when the iris reflects the iris photons, where the image of the iris having iris biometric data. Each retina imaging system has a retina illumination source adapted to emit retina photons to a retina of the right eye or the left eye and a retina image sensor configured to capture an image of the retina when the retina reflects the retina photons, where the image of the retina having retinal biometric data. The exemplary embodiment employs a controller adapted to control the at least one iris imaging system and the at least one retina imaging system. The iris image sensor of the at least one iris imaging system captures the image of the iris according to operation of the corresponding iris illumination source, and the retina image sensor of the at least one iris imaging system captures the image of the retina according to operation of the corresponding retina illumination source. 
     Other embodiments of the present invention provide a multimodal ocular biometric system that captures and processes images of the iris and/or the retina from both eyes. Biometrics based on data from both eyes are also more accurate and robust than using biometrics that include data from only the iris or only the retina from a single eye. For example, in another exemplary embodiment, a system for multimodal biometric identification employs a binocular-shaped image capture device that allows a user to look through the device to view an object external to the device with both eyes, while the iris of each eye is illuminated and an image of each iris is captured by an image sensor. 
     Embodiments may use different combinations and configurations of iris illumination sources, retina illumination sources, iris image sensors, and retina image sensors to capture data from more than one modality. For example, images of the iris and the retina of both eyes may be captured and processed. Meanwhile, yet further embodiments may employ varying techniques for illuminating the iris or the retina, tracking the position of the iris or the retina, and achieving the best possible images of the iris or retina. For example, the tracking of the iris (or retina) may be employed to capture the best possible image of the corresponding retina (or iris). 
     Still other aspects, features, and advantages of the present invention are readily apparent from the following detailed description, by illustrating a number of exemplary embodiments and implementations, including the best mode contemplated for carrying out the present invention. The present invention is also capable of other and different embodiments, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates an embodiment of the present invention with a quadruple-sensor, two-eye simultaneous configuration. 
         FIG. 2A  illustrates a retina auto-focus technique employed by an embodiment of the present invention. 
         FIG. 2B  illustrates another retina auto-focus technique employed by an embodiment of the present invention. 
         FIG. 2C  illustrates yet another retina auto-focus technique employed by an embodiment of the present invention. 
         FIG. 3  illustrates an embodiment of the present invention with a dual-sensor, two-eye flippable configuration. 
         FIG. 4  illustrates an embodiment of the present invention with a triple-sensor, two-eye sequential configuration. 
         FIG. 5  illustrates an embodiment of the present invention with a single-sensor, two-eye sequential configuration. 
         FIG. 6A  illustrates an external view of an embodiment of the present invention that captures iris images from both eyes. 
         FIG. 6B  illustrates another external view of the embodiment of  FIG. 6A . 
         FIG. 6C  illustrates the use of corrective eyewear with the embodiment of  FIG. 6A . 
         FIG. 6D  illustrates an internal view of the embodiment of  FIG. 6A . 
         FIG. 7  illustrates an exemplary fixation scheme as seen by the user. 
         FIG. 8A  illustrates another exemplary fixation scheme, as seen by the user when the user is misaligned along the X-, Y-, and Z-axes. 
         FIG. 8B  illustrates another exemplary fixation scheme, as seen by the user, when the user is misaligned along the Z-axis. 
         FIG. 8C  illustrates another exemplary fixation scheme, as seen by the user when the user is aligned along the X-, Y-, and Z-axes. 
         FIG. 9  illustrates an exemplary scheme for entering a personal identification number by pupil tracking. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention provide a multimodal ocular biometric system that captures and processes images of both the iris and the retina, from which data can be determined for biometric identification. Further embodiments provide a multimodal ocular system that captures and processes images of the iris and/or the retina from both eyes of a subject. Biometrics based on data provided by these embodiments are more accurate and robust than using biometrics that include data from only the iris or only the retina from a single eye. 
     Advantageously, the iris and retina present biometric features that are both independent and strongly coupled. They are independent in that they are extracted from different biological structures. On the other hand, the iris and retina biometric features are strongly coupled because there is a fixed geometric relationship between the iris and the retina. Specifically, the position and orientation of the eye is reflected simultaneously in both the iris and the retina. Further, the biometric features of the iris and the retina are on the same scale. The strong coupling between the biometric features of the iris and the retina not only facilitates the simultaneous capture of these biometric features, but allows these features to be cross-referenced or combined in a common feature space that preserves the geometric relationship between the iris and retina. In addition, the use of an iris system complements the use of a retina system. For instance, small pupils are generally an advantage for iris systems while large pupils are generally an advantage for retina systems. 
     Accordingly, embodiments of the present invention employ various configurations of at least one imaging system that captures iris images and retina images. For example,  FIG. 1  illustrates a two-eye simultaneous iris/retina combination system, which employs two iris imaging systems that respectively capture iris images of the right and left eyes, and two retinal imaging systems that respectively capture the images of the right and left retina, all simultaneously, or at least substantially simultaneously. Information from the imaging systems is used to accomplish retinal pattern recognition, iris pattern recognition, and biometric fusion. Moreover, the information from the individual imaging systems are used in combination to establish a host of attributes including, but not limited to, positioning, tracking, focus, and interpupillary distance. In addition, the multimodal ocular biometric system is especially well suited for image capture of both eyes when the user is not wearing corrective eyewear. Although many of the features of the present invention may be described with respect to the two-eye simultaneous iris/retina combination system shown in  FIG. 1 , other configurations, as described further below, can implement these features in order to combine iris and retina images for biometric identification. 
     Referring to  FIG. 1 , the multimodal ocular biometric system  10  includes an optical system which is symmetric for both the left eye  2  and the right eye  4 . The multimodal ocular biometric system  10  includes two camera sensors  110  to capture respective images of the iris in the right and left eyes. The system  10  also has two camera sensors  210  to capture respective images of the retina in the right and left eyes. As such, an iris imaging system  100  and a retina imaging system  200  are provided for each eye. Therefore, iris and retina images can be captured simultaneously, or at least substantially simultaneously. Preferably, the iris imaging systems  100  and the retina imaging system  200  are housed in a single image capture device  12 , as depicted in  FIG. 1 . 
     The biometric information collected from the system  10  includes iris patterns and retina patterns, from which biometric data can be extracted. Liveness detection, which detects whether the biometric information comes from a living source, may also be achieved with the system  10 . U.S. patent application Ser. No. 11/258,749, filed on Oct. 26, 2005, describes a Method and System for Detecting Biometric Liveness, and is entirely incorporated herein by reference. 
     Furthermore, as described in more detail below, by capturing images of both irises simultaneously, the system  10  is able to provide biometrics, such as interpupillary distance and limbus diameter for both the right and left eyes. Advantageously, measurements of the interpupillary distance and limbus diameter can be used to improve database searching during biometric identification, because they allow reference data to be binned and narrowed to a relevant subset of data before a search is conducted for matches based on iris codes or retinal codes. In this way, a comprehensive search of all reference data for biometric matching is not required. For instance, limbus diameters for the general population have a range of about 9.5 mm to 13.5 mm. Thus, if the system  10  measures a limbus diameter to be 10.5 mm, a subset of reference data covering individuals with limbus diameters in a range of 10.25-10.75 mm, rather than the entire database, may be searched. Compared to conducting a comprehensive search, the time to obtain a match with the reference data may improve by up to 8 times when narrowing the data down according to ranges of limbus diameter in this manner. Moreover, interpupillary distances for the general population have a range of ±10 mm. Obtaining a ±1 mm resolution would thus improve search times by up to a factor of 10. As a result, narrowing the search data according to limbus diameter and the interpupillary distance may improve search times by 80 (8×10), which may be significant for very large databases. Also, throughput can be enhanced by system memory caching based on bins for mid-sized databases in multi-machine systems. Considering N interpupillary distance bins, if N machines with N local system memories each have enough system memory to hold the entire bin for an interpupillary distance in the database, then database access is less likely to become a system bottleneck. 
     To capture the iris and retina images, the multimodal ocular biometric system of the present invention employs both iris illumination adapted to emit photons to the iris of an eye and retina illumination adapted to emit photons to the retina of the eye. In particular, the embodiment shown in  FIG. 1  employs LEDs (light emitting diodes)  120  and  220  to produce iris illumination and retina illumination, respectively.  FIG. 1  also shows that the iris and retina illumination uses separate LED&#39;s. Correspondingly, the camera sensors  110  are configured to capture iris images when the right and left irises reflect the emitted light from the illumination source  120 , and the camera sensors  210  are configured to capture retina images when the right and left retinas reflect the emitted light from the illumination source  220 . 
     Alternatively, other embodiments of the present invention may employ laser diodes rather than LEDs. In these alternative embodiments, the system can perform laser Doppler imaging using an addressable CMOS detector on specific regions of interest. Advantageously, this approach permits retinal liveness testing as well as retina vessel determination and contrast enhancement. 
     As depicted in  FIG. 1 , a controller  15  is operably connected to the iris illumination and the retina illumination, such as LED&#39;s  120  and  220 . The controller  15  manages the manner in which the iris illumination and the retina illumination emits photons to the irises or the retinas, respectively. As is known, the controller  15  may be a programmable processing device that executes software, or stored instructions. For example, the controller  15  may employ an external conventional computer networked with the image capture device  12 . Alternatively, a field programmable gate array (FPGA) or digital signal processor (DSP) may be employed on board the image capture device  12 . In general, the systems described herein may employ a controller, as well as other processors, that are either internal or external to the image capture devices, which house the illumination and sensor systems. 
     The wavelengths for illumination of the iris and retina may be in the near infrared (NIR) (700 nm to 1000 nm). Special filters or coated optics may be used in the optical train to select specific wavelengths to satisfy the 700 nm to 900 nm wavelength requirements for the ANSI specification for Iris Image Interchange Format (ANSI INCITS 379-2004), but still allow a visible color image. 
     Accordingly, in the exemplary embodiment illustrated in FIG,  1 , the iris illumination system of the present invention may operate to illuminate just the inner orbit of the eye. Preferably, the area of interest outside the field of view (FOV) of the iris camera  110  is not over-illuminated, as illumination outside the FOV can cause reflections off the cheek, forehead, or nose creating non-uniform illumination of the iris. This is especially the case for people who wear makeup containing TiO 2 . Moreover, illuminating the area outside the FOV of the camera is a waste of light and energy. Two arrays of LEDs  120  at a wavelength of 850 nm, for example, are masked and focused on the iris and sclera in order to create this uniform illumination. The illumination occurs at an angle of approximately ±15 degrees measured from the line of sight of the user in order to minimize retroreflection off the retina with the associated bright pupil corresponding to the iris image. The pupil must remain dark for image analysis and to meet ANSI INCITS specification. 
     Light reflecting off the iris passes through a broadband antireflection coated optical window  330  and is imaged back through the imaging system, through a dichroic beamsplitter  130 . The light then passes through a plastic or glass longpass filter  180  with a cutoff wavelength of 780 nm, for example. The longpass filter  180  prevents ambient visible light from entering the imaging system and creating noise in the image. The light is then focused with the iris imaging lens  190  to the image sensor  110 . In a particular embodiment, the sensor  110  is a CMOS (complementary metal-oxide semiconductor) detector with high sensitivity to NIR illumination. The CMOS detector may have square pixels, a wide angle format, and a global shutter. 
     In general, the iris imaging system of the present invention may have a refractive lens (a single or a series of lenses)  190  which images the iris to a CMOS image sensor  110  or, alternatively, a CCD (charge-coupled device) sensor  110 . The image capture device  12  may also employ reflective or a combination of refractive and reflection optics. The imaging sensor  110  may also have a global shutter or a rolling shutter. 
     In addition, embodiments may include an iris imaging system which uses digital processing algorithms for pupil tracking and iris focus measurement. For example, a pupil tracking algorithm may employ segmentation, e.g. a caliper technique, to determine pupil position. Meanwhile, an example of an algorithm for iris focus measurement is disclosed in application Ser. No. 11/526,096, filed on Sep. 25, 2006, which is entirely incorporated herein by reference. With these two features, the three dimensional position of the iris with respect to the device  12  is determined for both left and right eyes. For example, information regarding position along X- and Y-axes may be determined from the pupil tracking and information regarding position along the Z-axis may be determined from the iris focus measurement. Evaluation of this position data may determine when images of acceptable quality have been captured and should be utilized for biometric data. 
     As further illustrated in FIG,  1 , the retina illumination may employ a tracking system to illuminate the optic nerve head of the retina. For instance, arrays of LED&#39;s  220  at a wavelength of 880 nm spaced 1 mm apart are aligned to 1 mm diameter and 10 mm long hollow tubes. The hollow tubes create a homogenizing waveguide for the light emanating from them. Only a single element of the array is illuminated at a time corresponding to the determination of the pupil&#39;s position in space, as determined by the digital processing algorithms, including segmentation and focus measure. As such, analysis of the iris image yields pupillary positional information that may be employed to determine illumination of the corresponding retina. In other words, the pupil&#39;s position is used to determine which LED  220  in the array aligns most optimally with the retina and should be activated for illumination of the retina. Reference numeral  225  in  FIG. 1  illustrates a diffuser, which is placed over the ends of the tubes to create a 1 mm spot from the active LED  220 . 
     Alternatively, reference numeral  225  may refer to an LCD shutter, which can create a similar 2-dimensional series of singly activated illuminators that are 1 mm in diameter and imaged to the eye. Depending on the determination of the pupil&#39;s position in space, the LCD shutter  225  allows light from the illumination source  220  to pass through an appropriate section of the LCD device  225  to illuminate the retina. As further alternatives, scanning micro-optics or holographic elements may also be employed. 
     The light from the LCD shutter/diffuser/micro-optics  225  reflects off a polarizing beamsplitter (PBS)  230  creating S polarized light. This light is then imaged by the aspheric objective lens  240 , through a long pass plastic sheet filter with a 780 nm cutoff wavelength, to a 2 mm spot just before the nominal position of the cornea. The angle of the light entering the pupil is nominally 15.5 degrees temporal to and 1.5 degrees inferior to the line of sight of the user. The spot diameter is chosen to be smaller than the pupil so that light does not scatter off its edges causing excess noise in the retina image. The divergence of the light is approximately 10 degrees half angle. This allows for imaging of a large enough FOV to obtain a suitable retina image for pattern recognition. The retina image consists of the blood vessel pattern emanating from the optic nerve head. Absorption of the light by hemoglobin and oxyhemoglobin in the blood creates the outline of the blood vessel pattern. Demarcation of the optic nerve head may or may not be discernable. The LED&#39;s have three pulse duration settings that are cycled through (exposure bracketing) so as to accommodate for reflectance differences of the retina in the general population. 
     Light reflecting off the retina passes back through the long pass cutoff filter. This filter prevents ambient visible light from entering the imaging system and creating noise in the image. It also hides the imaging optics from the user. The light is then collected by the aspheric objective lens  240  to produce a real image just before the polarizing beamsplitter  230 . This real image is then imaged though the PBS  230  allowing only P polarized light to pass. The purpose of the PBS  230  is to increase the signal to noise ratio of the signal by rejecting any S polarized light reflected back through the system from other optical surfaces. An imaging lens followed by a cubic phase mask optic then images the light onto a camera sensor  210 . The camera sensor  210  may be a CMOS detector with high sensitivity to NIR illumination. The CMOS detector has square pixels, has a wide angle format, and has a global shutter. 
     The images of the retina are multiplied by specific digital filters. These filters are created for differences in dioptric power correction. The images are evaluated using a retina focus measure algorithm and the one with the highest contrast image is preferably utilized for biometric identification. An example of a retinal focus measure algorithm is described in application Ser. No. 11/785,924, filed Apr. 20, 2007, which is entirely incorporated herein by reference. 
     The illumination for the iris may have a different wavelength from the illumination for the retina. In one embodiment of the present invention, the retina is illuminated with light of a first wavelength, the light of the first wavelength being reflected from the retina to the retina image capturing device. The iris is illuminated with light of a second wavelength that is different from the first wavelength, the light of the second wavelength being reflected from the iris to the iris image capturing device. The first wavelength of light is selected to provide enhanced contrast between biometric features of the retina, such as a retinal vessel pattern, and the background in the captured image. Similarly, the second wavelength of light is selected to provide enhanced contrast for the biometric features of the iris. 
     If the iris illumination and the retina illumination occur at the same time or in near time, however, the iris illumination can introduce noise in the retina signal, or vice versa. To avoid introduction of noise between the illumination of the iris and retina, dichroic optics can be employed to allow wavelength separation from the different illumination sources, where light of one wavelength is directed to one sensor while light of a second wavelength is directed to another sensor. The illumination with special dichroic optics can be pulsed or run as a continuous wave. 
     More advantageously, to eliminate the introduction of noise between the illumination of the iris and retina, the iris illumination and the retina illumination can be separated by pulsing the individual LEDs with a synchronized offset. For instance, the iris and retina cameras can run at 30 frames per second offset by half a frame (16.5 ms) with a shutter (global, rolling or global-rolling hybrid) of 10 ms. The pulses from the LEDs occur at 10 ms so that neither camera sees light from the other illumination LEDs. The advantage of pulsing illumination with a synchronous offset is that it freezes motion, maximizes frame rate without having to use dichroics, and allows higher pulse energies which reduces gain on the camera, thereby increasing image quality. Furthermore, pulsing illumination with a synchronous offset permits the use of the same wavelength for the illumination of the iris and retina. 
     In general, both iris and retina illumination may use auto gain in order to correct for the proper exposure for correction of reflectance differences of the iris and retina. Alternatively, both iris and retina illumination bracketing (or exposure bracketing) may be used instead of auto gain. In this alternative approach, two or more illumination power settings are cycled through to bracket through all possible reflectance differences seen in the general population; for example: power setting  1  (pulse  1 )=10 units, power setting  2  (pulse  2 )=12 units, power setting  3  (pulse  3 )=14 units, where cycle=pulse  1 , pulse  2 , pulse  3 , pulse  1 , pulse  2 , pulse  3 , . . . an so on. One could also do this by keeping the power constant and cycling three different pulse durations; for example: pulse duration  1  (pulse  1 )=10 units, pulse duration  2  (pulse  2 )=12 units, pulse duration  3  (pulse  3 )=14 units, where cycle=pulse  1 , pulse  2 , pulse  3 , pulse  1 , pulse  2 , pulse  3 , . . . an so on. 
     Accordingly, in the embodiment shown in  FIG. 1 , the iris illumination can advantageously be pulsed at less than half the frame rate of the iris and retina cameras. The frame rates for both cameras are identical. The image of the iris is analyzed with the pupil tracking and iris focus measure digital processing algorithms. The X 1 , Y 1 , and Z 1  positions of the pupil of the iris are calculated. The user must move through the nominal Z N  position of the system which establishes the absolute position of the user. Until that time, the system assumes a relative position of the pupil based on pupil size. Iris images that are adequately in focus are collected and analyzed appropriately. As described above, the LED&#39;s have three power settings that are cycled through (exposure bracketing) so as to accommodate for reflectance differences of the iris in the general population. 
     As described previously, the positional information of the pupil is utilized to select the addressable retinal illumination LED that will cleanly enter the pupil. The retina illumination LED is pulsed at half a frame out of phase from the iris illumination. The pulse duration is less than half the frame rate. As described above, by synchronizing the iris and retinal frame rates of the camera at half a frame rate out of phase with each other and using short pulses, the full frame rate of each camera can be utilized while minimizing noise that may occur between the illumination of the iris and the retina. Illumination pulses with shorter time frames freeze motion and increase image quality. 
     The present invention may also employ a retina auto focus mechanism, which corrects for changes in retinal focus due to differences in uncorrected dioptric power and allows any corrective optical devices to be removed by the user. Corrective optical devices can cause aberrations and glare. Several techniques may be applied to achieve retina auto focus. 
     As shown in the retina imaging system  200  of  FIG. 2A , one technique for retina auto focus employs a motor  292  that moves the focus of the retina imaging lens  290  in specific dioptric value increments, along the arrow A as shown in  FIG. 2A . The system utilizes a retina focus measure algorithm comparing successive positions. If the system remains out of focus, the system uses this comparison to determine the direction in which it should move. 
     As shown in  FIG. 2B , another technique for retina auto focus employs wavefront coding technology using cubic phase plate and signal analysis.  FIG. 2B  illustrates a retina imaging system  200 B with an imaging lens with a cubic phase plate, indicated by reference numeral  294 . Contrary to the use of the motorized lens, there are no moving parts with wavefront coding. A cubic phase mask is placed in the system and the system is fully characterized with regard to dioptric power correction. Differences in dioptric power correction are calculated and specific digital filters are created for each dioptric power. When an image is taken, each of the filters is convolved with the image and the one with the highest contrast image is utilized. This configuration provides a robust system, which can be used at extreme temperatures, because there are no moving parts. 
     As depicted in the retina imaging system  200 C of  FIG. 2C , a third technique for retina auto focus uses an electroactive optical element  296 , which is a liquid crystal sandwiched between two pieces of glass with a specific electrode configuration on them. By activating the electrodes with different voltages, either a positive or negative dioptric correction may be created. This can be a single device or a stack of devices to create larger dioptric correction. 
     While the auto focus systems above have been described in terms of retina imaging, it is understood that such auto focus techniques are also applicable to an iris auto focus system. 
     In general operation, the multimodal ocular biometric system according to the present invention may be handheld, but may also be attached to an articulating arm, attached to or embedded into an immovable object such as a wall, or adapted to an existing optical system such as a rifle scope or tank periscope. As described further below, the system may possess a simple fixation system, or interface, to position the user. For instance, with an exemplary handheld embodiment, the user picks up the device and removes any eyeglasses the user may be wearing. The user then identifies a fixation illumination source within the device and carefully positions the device with respect to his or her face according to the fixation illumination source. As also described in another embodiment below, the outer housing of the device may be designed to help center the user as well as to provide light baffling of external ambient light. 
     With reference to  FIG. 1 , the user operates the image capture device  12  by identifying the fixation light source  310  through the broadband antireflection coated windows  330 . The light from the source  310  reflects off the beamsplitter and cold mirror  320 . In a fixation system  60  illustrated in  FIG. 7 , a circular target  62  with cross hairs  64  is viewed through an imaging lens with two illuminated bars  66  above and below the lens. The illuminated bars  66  are positioned at the exit pupil of the device  12 . The bars  66  may include a diffusing light guide with colored LEDs illuminating them. The circular target  62  is a reticule with a diffuser and colored LEDs behind it. The user operates the fixation system  60  by moving the device  12  relative to his or her eyes to center the circle  62  between the two bars  64 . As the user moves back and forth relative to the device  12 , different colored combinations may help guide his or her movement. 
     The image capture device  12  may also employ provide positional feedback to the user by using the pupil tracking and iris focus measure digital processing algorithms. A retina focus measure digital processing algorithm can be used in place of, or in combination with, an iris focus measure digital processing algorithm. 
     In another fixation system  70  illustrated in  FIGS. 8A-C , an interface provides a set of central cross hairs  72  designating nominal positioning (X N , Y N , Z N ) for optimal alignment by the user relative to the device  12  and a second set of cross hairs  74  with a circle  76  designating the user&#39;s present position (X 1 , Y 1 , Z 1 ). When the user moves along the X- and Y-axes (left, right, up and down as shown in  FIGS. 8A-C ), the cross hairs  74  with the circle  76  correspondingly move along the X- and Y-axes. When the user moves back and forth relative to the device along the Z-axis the diameter of the circle  76  becomes larger as the user moves away from the nominal Z N  position and smaller as the user moves towards the nominal Z N  position. When the circle  76  disappears, the user is positioned at the nominal Z N  position. Furthermore, when the user sees only a single set of cross hairs, the second set of cross hairs  74  overlaps with the central cross hairs  72 . Therefore, the image of  FIG. 8A  indicates that the user is misaligned along the X-, Y-, and Z-axes. Meanwhile, the image of  FIG. 8B  indicates that the user is aligned along the X- and Y-axes, but misaligned along the Z-axis. When the interface shows the image of  FIG. 8C , the user has achieved the nominal position (X N , Y N , Z N ). Auditory feedback may be additionally employed with the fixation system  70 , signaling the user with appropriate tones and/or verbal instructions to move the user into optimal alignment. 
     As shown in  FIG. 9 , embodiments of the present invention may include, in combination with the fixation system, a clock interface  80  that accepts a pin number for further identification. When users look into the device, they begin by looking at a start position. They then enter their pin number by fixating on the numbers or other symbols  82 . The system uses the pupil tracking to determine the trajectory of the different pupil positions to identify each number or symbol  82  entered by the user. Verification of each number or symbol  82  can be indicated through aural tones and/or visible color changes, as illustrated by number  83  in  FIG. 9 . 
     In addition to the two-eye simultaneous iris/retina combination system shown in  FIG. 1 , other configurations can be employed to combine iris and retina images. A left-eye only configuration employs iris and retina imaging systems to capture images of the left eye only. Similarly, a right-eye only configuration employs iris and retina imaging systems to capture images of the right eye only. 
     As shown in  FIG. 3 , a dual sensor, two-eye “flippable” system  20  provides one iris imaging system  400  and one retina imaging system  500  in an image capture device  22  that can be oriented to capture images of both the left and right eyes, in succession. In particular, the same iris imaging system  400  and retina imaging system  500  are used to capture images of the left and right eyes. Once images of one eye are captured, the user flips, or turns the device over, to capture images of the second eye. Flipping the device over maintains the correct orientation of the iris and retina imaging systems with respect to the eye. For example, the specific orientation shown in  FIG. 2  permits the capture of images from the right eye  4 . 
     Similar to the iris imaging system  100  described previously, the iris imaging system  400  in  FIG. 3  employs a camera sensor  410  which captures images of the illuminated iris through a dichroic beamsplitter  430 . Similar to the retina imaging system  200  described previously, the retina imaging system  500  in  FIG. 3  employs an illumination source  520  that provides light that is guided through a LCD shutter/diffuser/micro-optics  525 , a polarizing beamsplitter (PBS)  530 , and an aspheric objective lens  540  to the retina. Furthermore, the image of the retina then passes back through the aspheric objective lens  540  and the PBS  530  to the camera sensor  510 . The system  20 , however, employs a dual fixation LED with orientation sensor  525 , where one of the two LED&#39;s is activated according to the “flipped” orientation of the device  22 . An orientation sensor senses the orientation of the device  22  and correspondingly turns on the appropriate fixation LED. 
     Moreover, the system  20  as shown in  FIG. 3  also uses a dual retina/iris illumination and retina illumination tracking configuration. In other words, the illumination source  520  provides illumination of the iris as well as the retina. The retina illumination system in this embodiment is similar to the illumination system for the retina in the two-eye simultaneous system  10  shown in  FIG. 1 , where the element of the LED array is illuminated according to the pupil&#39;s position in space. The captured iris image is used to track the position of the pupil in order to identify the specific LED that should be used to provide the necessary pinpoint illumination of the retina in the subsequent image capture. Here, however, both the retina illumination and iris illumination emanate through the retina imaging optics. The addressable light source array  520  is used to create pulsed light for both iris and retina illumination. All elements in the array  520  are employed to illuminate the iris. Then, using the pupil tracking digital processing algorithm and iris focus measure digital processing algorithm, selected elements in the array are turned on to illuminate the retina. As the position of the iris moves the appropriate elements in the array are selected for both the retina and iris. For the retina illumination, the illumination elements of the array imaged (to just before the retina) are smaller than the pupil of the iris. Advantageously, this illumination configuration enables simplification of the packaging, minimizes reflections off the orbit of the eye for uniform iris illumination, and allows scanning of the retina for increased volume of alignment. As described above, the addressable light source array can be built in several different configurations, including, but not limited to, the use of an LED array with light guides and diffuser and an LCD shutter, scanning micro-optics, and holographic elements, as indicated by reference numeral  525 . 
     In another embodiment illustrated in  FIG. 4 , a triple sensor, two-eye sequential system  30  employs one iris imaging system  600  and two retina imaging systems  700  in device  32  to capture sequential, or successive, images of both the left and right eyes. The same iris imaging system  600  is used to image the iris of both the left and right eyes, while two retina imaging systems  700  with specific left and right orientations are used to image the left and right eyes, respectively. Unlike the two-eye flippable system  20 , the system  30  of  FIG. 4  does not have to be flipped, or turned over, to capture images of the second eye. Thus, it easier to reposition for capture of images from the second eye, because the same horizontal plane can be maintained. In addition, a dual fixation LED with orientation sensor does not have to be employed. Rather, a single fixation source  310  may be employed. 
     Similar to the iris imaging system  100  described previously, the iris imaging system  600  in  FIG. 4  employs a camera sensor  610  which captures images of the illuminated iris through a dichroic beamsplitter  630 . Similar to the retina imaging system  200  described previously, the retina imaging system  700  in  FIG. 4  employs an illumination source  720  that provides light that is guided through a LCD shutter/diffuser/micro-optics  725 , a polarizing beamsplitter (PBS)  730 , and an aspheric objective lens  740  to the retina. Furthermore, the image of the retina then passes back through the aspheric objective lens  740  and the PBS  730  to the camera sensor  710 . 
     In yet another embodiment shown in  FIG. 5 , a single-sensor, two-eye sequential system  40  includes a single sensor  810  in device  42  to capture both the retina and iris images by employing pulse separation and different wavelengths for the iris and retina. Wavelength multiplexing can be implemented with this embodiment, where a single optic with two surfaces with different coatings permits the capture of different images corresponding to particular wavelengths. For instance, λ 1 =810 nm and λ 3 =880 nm can be used to capture images of the iris, while λ 2 =850 nm and λ 4 =910 nm can be used to capture images of the retina. The two coated surfaces on the single optic permit sequential detection of λ 1 , λ 2 , λ 3 , and λ 4  and capture of alternating images of the iris and retina. In general, several optical systems can be used to get the images of both eyes on a single detector array. Like the systems described above, the system  40  shown in  FIG. 5  employs an LED array  820 , a LCD shutter/micro-optics/diffuser  825 , a polarizing beamsplitter (PBS)  830 , an aspheric objective lens  840 , and a single fixation source  310 . However, a compensating lens  865 , an extra reflective mirror  860 , and a dichroic beamsplitter  870  are additionally used in order to form images of the retina and the iris on the same camera sensor  810 . The compensation lens allows for proper image magnification for the capture of the iris by camera sensor  810 . Moreover, similar to the system  20  of  FIG. 3 , the system  40  uses a dual retina/iris illumination and retina illumination tracking configuration. The advantage of this system is that it uses a single sensor and fewer parts. However, the disadvantage is that the system runs at half the frame rate for iris and retina image capture being every other frame respectively. In other words, halving the frame rate yields half the number of images of the retina and the iris, so it may be more difficult to obtain adequate images. In addition, this particular configuration must also be flipped like the dual sensor, two-eye flippable configuration shown in  FIG. 2 . 
     When the retina illumination tracking system described above is used with symmetric iris/retina camera combinations to allow simultaneous capture of both eyes, such as the two-eye simultaneous system  10  of  FIG. 1 , one achieves automatic interpupillary adjustment without the need for any moving parts. Interpupillary distance measurement can be determined, providing an additional biometric. With information regarding position along the X- and Y-axes from the pupil tracking algorithm and information regarding position along the Z-axis from the focus measure algorithm, the (X, Y, Z) position of each pupil can be used to calculate pupil separation. As described above, this particular biometric is used to reduce database searching for iris matching, retina matching and iris retina fusion matching Additional on axis illumination of the iris can also enable bright pupil back reflection (“red eye”) that can enhance the iris/retina tracking algorithms. 
     While all the embodiments above capture and process a combination of iris and retina images, other embodiments of the present invention may capture and process either images of the iris or the retina from both eyes of a subject. As described previously, biometrics based on data from both eyes are more accurate and robust than using biometrics that include data from only the iris or only the retina from a single eye. Illustrating a corresponding exemplary embodiment,  FIGS. 6A-D  show a device  50  adapted to simultaneously accommodate both eyes of a user, similar to a pair of binoculars, and capture images of both irises. As shown in  FIGS. 6A-D , the user employing the device  50  is able to see through the device  50  to view an object external to the device  50  as a target. In particular, with the device positioned at the user&#39;s right and left eyes, the user looks into the user windows  902  and through opposing windows  904  to view the external object, or target, on the other side of the device  50 . Unlike the embodiments described previously, the device  50  may be employed without a fixation illumination source. The device  50  employs a fixation system where the exit pupil matches or is slightly larger than the entrance pupil of the eye for a given eye relief Using a two-eyed simultaneous configuration accommodating both eyes, an elliptical, or near elliptical, exit pupil is used to accommodate interpupillary distance. This maintains vertical alignment and allows vergence by the user to maintain horizontal alignment. The target may be an image which appears to be at a distance. Advantageously, this causes the brain to allow the eye to relax to its unaccommodated state. 
     In particular,  FIG. 6A  shows the biometric device  50  with housing  900 . In general, users begin by looking through the user windows  902  and bringing the device  50  closer to their eyes until they are able to use their vergence to visually fuse the exit pupils of the device  50 . This approach aligns most users to a given image plane with or without eyeglasses. As shown in  FIG. 6B , the device  50  also has opposing windows  904  facing the opposing user windows  902 . The opposing windows  904  not only permit an image of the target on the other side of the device  50  to be seen by the user, but the opposing windows also allow one to see the eyes of the user positioned at user windows  902 . As a result, in addition to operation of the device  50  directly by the user, the device  50  also permits operation by another person who holds the device  50  at the user&#39;s face and aligns it to the user&#39;s eyes from the other side. Thus, the device  50  allows an operator to assist a user during alignment and operation of the device  50 . 
     With its binocular-like shape, the device  50  helps to ensure proper alignment about at least two axes of rotation in order to achieve a better biometric. With reference to the X-, Y-, and Z-axes shown in  FIG. 6A , when users bring the device  50  to their face, they have to position the device  50  so that they can see through both user windows  902 , thus ensuring proper alignment about the Z-axis. Moreover, in order to look into the device  50  more easily, users naturally position the device  50  so that the user windows  902  are approximately the same distance from each respective eye, which ensures proper alignment about the Y-axis. As described above, the exit pupils can then be elliptical, or slit-like, to minimize any misalignment about the X-axis. 
     Additionally, to obtain more precise alignment of the user&#39;s eyes, a linear horizontal diffraction grating, or equivalent “microlouver” technology, may be placed on user windows  902  in order to limit the field of view of the user or operator and ensure proper alignment along the vertical Y-axis. A second vertical diffraction grating may also be employed to also ensure proper alignment along the horizontal X-axis. The combination of horizontal and vertical gratings limits the field of view vertically and horizontally. Moreover, a semitransparent target may be placed behind the gratings for additional alignment indicators. 
       FIG. 6D  illustrates an arrangement of components that may be employed by device  50  to capture images of the irises of both eyes positioned at user windows  902 . Two camera sensors  910  with filters  912  are positioned on opposite (right and left) sides in the interior of the device  50  to capture respective images of the right and left eyes. The LEDs  920  provide near infrared illumination to the iris of each eye. The illumination is reflected from the irises back to the respective beamsplitters  930 . The beamsplitters  930  may be “hot” mirrors which redirect the near infrared light reflected from the irises to the respective camera sensors  910 , but which allow visible light to pass through to the operator windows  904  so that an operator can see the user&#39;s eyes. White light illumination from the white light illumination sources  950  may be employed to close down the pupil of the user to provide better biometric data and to help illuminate the eye for alignment by an operator. As shown in  FIG. 6A and 6D , the area  922  of near infrared light cast by the LEDs  920  is smaller than area  952  of white light cast by sources  950 . With a smaller area  922 , the amount of near infrared light reflected from the area outside the iris, such as the user&#39;s cheeks, is minimized. 
     In order to facilitate the use of the device  50  by an individual who requires corrective eyeglasses, the device  50  may accommodate the individual&#39;s eyeglasses  7 , as illustrated in  FIG. 6C . For instance, the individual&#39;s eyeglasses  7  may be combined with the device  50  beyond the beamsplitters  930  but in a position where the eyeglasses can sufficiently correct the person&#39;s vision in order to use the device  50  and view the external object. Accordingly, illumination and image capture are not affected by the eyeglasses. 
     It is understood that a device similar to the device  50  illustrated in  FIGS. 6A-D  may be used to capture images of the retina from both eyes. Of course, another similar device may be employed to capture images of both the iris and the retina of both eyes, in a manner similar to embodiments described previously. 
     As described above with reference to  FIG. 1 , the controller  15  may be a programmable processing device, such as an external conventional computer networked with the device  12  or an on-board field programmable gate array (FPGA) or digital signal processor (DSP), that executes software, or stored instructions. Controllers  25 ,  35 , and  45  shown in  FIGS. 3 ,  4 , and  5 , respectively, may be similarly configured. In general, physical processors and/or machines employed by embodiments of the present invention for any processing or evaluation may include one or more networked or non-networked general purpose computer systems, microprocessors, field programmable gate arrays (FPGA&#39;s), digital signal processors (DSP&#39;s), micro-controllers, and the like, programmed according to the teachings of the exemplary embodiments of the present invention, as is appreciated by those skilled in the computer and software arts. The physical processors and/or machines may be externally networked with the image capture device, or may be integrated to reside within the image capture device. Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the exemplary embodiments, as is appreciated by those skilled in the software art. In addition, the devices and subsystems of the exemplary embodiments can be implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as is appreciated by those skilled in the electrical art(s). Thus, the exemplary embodiments are not limited to any specific combination of hardware circuitry and/or software. 
     Stored on any one or on a combination of computer readable media, the exemplary embodiments of the present invention may include software for controlling the devices and subsystems of the exemplary embodiments, for driving the devices and subsystems of the exemplary embodiments, for enabling the devices and subsystems of the exemplary embodiments to interact with a human user, and the like. Such software can include, but is not limited to, device drivers, firmware, operating systems, development tools, applications software, and the like. Such computer readable media further can include the computer program product of an embodiment of the present inventions for performing all or a portion (if processing is distributed) of the processing performed in implementing the inventions. Computer code devices of the exemplary embodiments of the present inventions can include any suitable interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs), Java classes and applets, complete executable programs, and the like. Moreover, parts of the processing of the exemplary embodiments of the present inventions can be distributed for better performance, reliability, cost, and the like. 
     Common forms of computer-readable media may include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other suitable magnetic medium, a CD-ROM, CDRW, DVD, any other suitable optical medium, punch cards, paper tape, optical mark sheets, any other suitable physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other suitable memory chip or cartridge, a carrier wave or any other suitable medium from which a computer can read. 
     While the present invention has been described in connection with a number of exemplary embodiments, and implementations, the present inventions are not so limited, but rather cover various modifications, and equivalent arrangements, which fall within the purview of prospective claims. For example, the positions of the iris camera and the fixation illumination source in embodiments above may be switched by the use of a “hot” mirror which reflects the iris image. Similarly, the positions of the retina camera and the retina illumination may be switched by illuminating the retina with P polarized light and imaging the S polarized light. 
     As a further example, while embodiments may capture retina images from both eyes, only the best retinal image from both eyes may be retained to ensure useable retinal biometric data. As a result, for a two-eye simultaneous configuration, the embodiment produces data regarding the pupillary distance as well as biometric data from both irises and one of the two retina. 
     Moreover, although the exemplary embodiments discussed herein are combination retina and iris imaging systems used for human identification, the multimodal ocular biometric system of the present invention is not limited to human identification and can be used for animal identification.