# Patent

## Title
Iris recognition system using quality metrics

## Abstract

A system for iris recognition using a set of quality metrics, which may include eye image validation, blur assessment, offset, gazing, obscuration, visibility, and the like. These metrics may be established as quantitative measures which can automatically assess the quality of eye images before they are processed for recognition purposes. Quadrant iris analysis, histograms, map processing enhancements, and multi-band analysis may be used in aiding in the iris recognition approach.

## Background
BACKGROUND
The present invention pertains to biometrics and particularly to identification of persons using biometrics. More particularly, the invention refers to identification via eye images.
SUMMARY
The invention is an iris recognition system using iris quality metrics on acquired eye images.



BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a diagram of the architecture of the present image analysis system;
FIG. 2 is a diagram for eye image validation;
FIGS. 3a, 3b, 3c and 4 are diagrams for image blur assessment;
FIG. 5 shows a diagram and information for eye gazing and offset determinations;
FIGS. 6a and 6b show information and a diagram relative to eye obscuration;
FIGS. 7a and 7b show information and a diagram pertaining to quadrant based iris segmentation analysis;
FIGS. 8 and 9 are histograms showing pixel clustering based on distribution; and
FIG. 10 is a diagram of one, two and three banks of code bits related to iris analysis.



DESCRIPTION
The present invention may include methods and apparatus for developing quantitative measures that can automatically assess the quality of iris images before being processed for iris recognition.
Digital eye images are often subject to a wide variety of distortions during acquisitions, transmission and reproduction any of which may result in degradation of iris recognition performance.
Several patent applications may be relevant to the present invention. U.S. patent application Ser. No. 10/979,129, filed Nov. 3, 2004, is hereby incorporated by reference. U.S. patent application Ser. No. 11/275,703 filed Jan. 25, 2006, is hereby incorporated by reference. U.S. patent application Ser. No. 11/372,854, filed Mar. 10, 2006, is hereby incorporated by reference. U.S. patent application Ser. No. 11/681,614, filed Mar. 2, 2007, is hereby incorporated by reference. U.S. patent application Ser. No. 11/043,366, filed Jan. 26, 2005, is hereby incorporated by reference. U.S. patent application Ser. No. 10/655,124, filed Sep. 5, 2003, is hereby incorporated by reference. U.S. patent application Ser. No. 11/672,108, filed Feb. 7, 2007, is hereby incorporated by reference. U.S. patent application Ser. No. 11/681,751, filed Mar. 2, 2007, is hereby incorporated by reference. U.S. patent application Ser. No. 11/681,662, filed Mar. 2, 2007, is hereby incorporated by reference. U.S. patent application Ser. No. 11/675,424, filed Feb. 15, 2007, is hereby incorporated by reference. U.S. patent application Ser. No. 11/382,373, filed May 9, 2006, is hereby incorporated by reference.
The present invention may include an implementation of a set of appropriate quantitative iris image quality metrics (IQM's). The IQM's may be defined on the basis of image features based on the acquisition performance. The quality of the image should correlate well with subjective iris processes. The IQM's may be integrated into a processing procedure to assess the quality of the iris image before and through out the iris recognition process. Based upon the evaluation of these metrics, a case based reasoning (CBR) approach may be executed to process the iris image based upon its quality.
It appears desirable to assess the quality of an eye image in real-time as a quality control procedure. This may allow poor image acquisition to be corrected through recapture and facilitate acquisition of the best possible image within the capture time window configured in the system. This may result in a process of more good quality iris images that can improve the iris identification accuracy and the integrity of iris recognition systems. A perfectly captured iris pattern under ideal conditions would illustrate clearly the texture of an iris that can be captured in a unique iris barcode. However, many factors such eye closure, obscuration, off-angle eyes, occlusions, and imperfect acquisition embedded in electronic noise, non-uniform illumination, different sensor wavelength sensitivity, pupil dilation, and specular light reflections, may cause the captured iris map to be far from having ideal quality. Smearing, blurring, defocus and poor resolution may result in the capture of very poor quality images as that will have a negative impact on even iris segmentation and/or feature extraction.
The present metrics may be used to improve upon the iris recognition using quadrant based analysis (starting from sclera edges to lid edges) and to extract iris features in constructing the iris polar map based upon the computed IQM's of the digital iris image. Based upon the amount of the artifacts, from obscuration, occlusion, or blurring or other effects, a process may be applied based upon the case based (CBR) reasoning approach.
IQM1 through IQM6 may be defined herein. IQM1 is eye validation. Eye validation may be assessed using the pupil edges (i.e., inner border of the iris) and determining how they fit to an elliptic model. One may analyze the model fitting into multi-stages where the edges are analyzed against an elliptic fit, and then to a circular fit. If either model fails, presumably because of an obscured eye, one may mask the upper lids and re-assess only the sclera and bottom lids against a model fit. The displacement of the curve from the model may be a measure of the quality of the eye.
IQM2 is blur amount. Properties of a neighborhood pixel distribution may be considered using a gradient of the iris texture. By assumption, the isotropic derivative of an image may show located edges at the borders of the iris consistently regardless of image quality (blur or focused images), which means a quantified amount of edges are expected to be in the image gradient as a function of the expected range of at least the inner border of the iris. The method of locating other edges is characteristic of the “gradient filter” family of edge detection filters. So for non-blur images, one may expect additional detected edges which exceed the amount associated with the inner borders. Thus, an image may be declared non-blur if the value of the cumulative sum of the gradient exceeds the expected range of the inner border of the iris.
There may be several scores for quality and matching. One is quality (Q1) relating to the query which should be 100 percent. Another is quality (Q2) of the probe or image. Still another score (M) is a matching score. The two scores, Q2 and M, are the scores which may be used in the present approach. IQMs 1, 2, 5 and 6 may be relevant to decision making in matching subjects and be used to tailor difference processes for different acquisition scenarios.
IQM3 may be an off angle or gazing measure of an eye in an image. The off angle may be assessed in an iris outer boundary shape fitting. One may measure the ratio between the major and minor axis of the elliptic fit of the pupil which can be a good indicator of the off angle or gazing of the eye.
IQM4 is a simple test of the location of the eye within the eye image. If the eye is close to the edges of the image by at least the expected maximum size of an iris radius, it can be considered an offset eye as it may not contain the entire bounds of the iris.
IQM5 is an amount of iris exposure within the iris map. IQM6 is similar to IQM1 but is applied to the outer border of the iris rather than the inner border.
The logical flow of processes may be influenced by the quality of the iris. An architecture design of the solution using the IQM's is described herein. Several procedures of the invention may be implemented with an algorithm. The segmentation analysis may be reconfigured based upon a quadrant approach where one uses a POSE (polar segmentation) technique (U.S. patent application Ser. No. 11/043,366, filed Jan. 26, 2005). The POSE type segmentation may start at the sclera edges and expand the edge detection to the lids quadrants (obscured areas). In the presence of obscuration (detected using the discontinuity in the derivative of the edge curve at the lid quadrants), one may mask the iris map accordingly based upon the amount of obscurations. Two selective operations may be defined. One is to mask the lid region entirely for heavy obscuration. Another is, for partial obscuration, to use the two breaking points of the discontinuity on the curve to interpolate a linear curve and extract just the iris pixels contained between the constructed line and pupil borders while masking the region outward the curve.
One may also model the iris map intensity using normal distributions to identify any outliers that do not fit the iris profile. The procedure may detect any artifacts due to reflection and or to some missed edges in the segmentation process.
To extend to at-a-distance applications, some of the algorithm procedures may require exhaustive processes which include Hough transforms. Some issues with a Hough method may include requiring threshold values to be chosen for edge detection, which may result into critical information (e.g., edge points) being removed/missed, and thus resulting in a failure to detect the iris or pupil regions.
FIG. 1 is a diagram of the architecture of the present invention or system 10. The first item is a locate-eye function block 11 which contains an eye finder 12. Upon finding an eye, the finder 12 may output the eye image to a blob analysis unit 13. The results of the blob analysis may be evaluated with IQM's for parameter estimates to stage the parameter ranges.
IQM1 may be indicated whether there the image has a valid eye at symbol 21. IQM1 is described in FIG. 2 and corresponding text hereon. If the capture of the eye in not deemed valid, the process might stop as symbol 31. If valid, then the eye image may go to symbol 22 for a blur measure according an IQM2, as described in FIGS. 3 and 4, and corresponding text herein. If the results of IQM2 at symbol 22 relative to a blur measure are not good, then the process may stop at symbol 32. If the results of IQM2 evaluation at symbol 22 are acceptable, then the pupil may be a segmented at block 14. After block 14, a gazed eye measure may be made at item 23 in view of an IQM3. Also, an eye may from the blob analysis unit 13 may to go an offset or shifted eye block 24 for an eye offset or shift measurement according to IQM4. IQM3 and IQM4 are described in FIG. 5 and corresponding text herein. The eye offset measurement from block 24 may be joined with the output of gazed eye measurement from block 23. These outputs may go to symbol 15 where a question whether the eye of the image is offset or gazed. If the eye is offset or gazed, then the iris may be segmented with no-circular calibration at block 16. If the eye is not offset or gazed, then the iris may be segmented with circular calibration at block 17.
The segment iris at the output of block 16 or 17 may go to a symbol that checks whether the eye or iris is obscured according to IQM6, as shown in FIG. 6 and corresponding text herein. If the result of symbol 26 is not acceptable, then the process may stop at symbol 36. If it is acceptable, then the eye or iris image may go to a block 18 where a map of the iris may be extracted. From block 18, the resultant map image may go to a symbol 25 where a visibility measure is made according to IQM5, as shown in FIGS. 6a and 6b and corresponding text herein. If the measure is not acceptable, the process may stop at symbol 35. If acceptable, then a multi-band code may be made of the iris at block 19. Also a single band-code may be made at block 27. Either or both codes from blocks 19 and 27 may go to a block 28 for a match to identify the iris and indicate possibly the identity of the person associated with the iris. Also, the one or both codes may be indexed and stored in a database for future use, such as identification.
IQM1 for eye validation, as shown in FIG. 2, may begin with an elliptic fitting having a controlled samples consensus algorithm (CSCA) at block 41. Following block 41, the fitness may be computed as a number of edges within a range of the estimated ellipse/total number of edges at block 42. The fitness may be checked at symbol 43 to note that it is less than THR1. If not, stop process and return quality 85.
Circular fitting on a Hough-based method may be implemented on the iris at block 44. The fitness may be computed as a number of edges within a range of the estimated circle/total number of edges at block 45. The fitness may be checked to see that it is less than THR2 at symbol 46. If not, then stop process and return quality 86. After symbol 46, an upper portion of the iris contour may be masked at block 47. Circular fitting may be done with the Hough-based method at block 48. At block 49, fitness may be computed as a number of edges within a range of the estimated circle/total number of non-masked regions or portions edges. One may go to return quality 87.
It may be noted that at least four combinations can be used to fit an elliptic model using the guided CSSA algorithm as a modification to random consensus algorithm and replacement of Hough transform. They include the sclera only, sclera plus the lower lid, the entire contour, and the lower portion of the contour.
FIG. 3a is an outline of the IQM2 image blur assessment or measure. An eye image 50 may go to a block 51 to be decimated at, for instance, M×N=120×160. An operator may be applied to the decimated image at block 52. An example may be a Sobel operator 29 shown in FIG. 3b. An output after an application of the operator may go to a gradient equation at block 53, such as for example a Scharr filter 33 shown in FIG. 3c. The value of the output of block 53 should have a value greater than “θ” as indicated at symbol 54 to be acceptable.
A basic concept of the image blur assessment or measure IMQ2 may be noted in conjunction with a pixel distribution. Properties of a neighborhood pixel distribution may be considered using a gradient of the overall acquired image. The isotropic derivative operator on the image may show located edges at the borders of an iris consistently regardless of image quality (e.g., blur or focused images), which means that a quantified amount of edges is expected to be in the image gradient. For instance, θ=(2π(Rin+Rout))/(M×N). In the present example, θ=(2π(18+38))/(120×160)≈0.018. However, a value smaller than this estimate may be deemed as a blur image, and any value comparable or higher than this number may be deemed to be non-blur. This approach or method of locating other edges may appear characteristic of the “gradient filter” family of edge detection filters and includes an operator. Thus, for non-blur images, one may expect additional detected edges that exceed the amount computed for θ. An image may be declared a blur if the value of the cumulative sum of the gradient exceeds the computed threshold θ.
Another concept of the image blur assessment or measure IMQ2 may be noted in conjunction with FIG. 4. A zero crossing may be applied to find edges at all directions. A Laplacian approach may find edges regardless of orientation. One may look for a zero-crossing second derivative, that is, a Laplacian approach may be applied using a derivative for 1st-derivative extrema. It may be a Laplacian of the Gaussian (LOG) (linear and isotropic),

LoGσ=−(1/(πσ4)) (1−(x2+y2/2σ2))e−((x2+y2)/2σ2)).

Thus, one may search for the zero crossings of a Gaussian smoothed image with an operator 40. An example of an operator 40 may be a Marr-Hildreth one.

An image 60 of an eye may be provided to a block 61 for a crop at center, as indicated by a rectangle 55 of image 60 and with a formula (2Rout)×(2Rout). The cropped image encompassing the iris of the eye may go to blocks 62 and 63 for Gaussian smoothing and application of a formula, for example,




  
    
      
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          ∂
          y
        
      
    
  
  ,




which together constitute the operator 40. The operator should preserve the texture of the image. Another formula may suffice for block 63. The output from block 63 may to a block 64 for a filtering or evaluation with a formula, for example,





  
    1
    
      4
      ⁢
      
        R
        OUT
        2
      
    
  
  ⁢
  
    
      ∑
      
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    ⁢
    
      
        ∇
        
          I
          ⁡
          
            (
            
              x
              ,
              y
            
            )
          
        
      
      .
    
  




Another formula may suffice for block 64. The output of block 64 may be checked at symbol 65 to see whether it exceeds “θ”, where θ=(π(Rin+Rout))/2Rout.

Eye gazing and offset may be evaluated in accordance with IQM3 and IQM4, respectively. Items of FIG. 5 illustrate such evaluation. A measurement may be made to assess the deformation of the iris perspective projection. The dimensions of the iris may be “b” (minor axis) and “a” (major axis), for instance a measurement of the outer bound in a direction along the y axis and in a direction along the x axis, respectively, as indicated by item 56. The measurement for deformation assessment may be indicated by a formula in box 57. The gazing deformation can be estimated using an approximation as being indicated by a formula. An applicable formula may be




  
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which may be approximated by formula,





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Computing the surface of the inner bound may be another approach. For an aspect ratio of 0.36<(b/a)<2.94, the maximum error should be about 5 percent. For an aspect ratio of 0.12<(b/a)<10.77, the maximum error should be about 10 percent. A rough estimation of area may be indicated by “πab” in box 58. A calculation relative to offset can be computed by validating the center of the model C(x,y) such as the Rmax of the model satisfies the formulas in box 59. which are





  
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c may be the center and Rmax=max expected value of the radius of the estimated model (E[radius]). If one measures the outer bound from the center of the iris along the x axis, and the distance in the x direction is less than the maximum radius of the outer bound Rmax, then there may be an offset.

The visibility measure according to IQM5 and obscuration measure according to IQM6 are shown in FIG. 6a. The outer boundary of the iris may be fitted into a model. A fitness measure is how good the model may fit the curve of the boundary. It the conditional statements 66 and 67 are met, then the statement 68 for an IQM5 visibility measurement may follow. Statement 66 is




  
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and statement 67 is





  
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Statement 68 is





  
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A statement 69 for an IQM6 measurement is





  
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FIG. 6b shows maps 34, and portions that should be masked to eliminate noise.

FIGS. 7a and 7b provide an approach for quadrant iris analysis, that is, an analysis quadrant by quadrant. Step 1 may include finding limits on the top left quadrant 71. One may start from the sclera at an x axis, clockwise, and proceed to a break point at an obscuration or discontinuity, if any. If there is no obscuration, discontinuity or the like, then a break point may be defined between the first and second quadrants (i.e., upper left and right quadrants). Such defined break may be about 90 degrees or so clockwise from the 0 degree point at the x-axis in the first quadrant or about 90 degrees counterclockwise from the 180 degree point from the x-axis in the second quadrant.
The statements in box 75 may be used for quadrant analysis as indicated herein.



  
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Step 2 may include finding limits of the top right quadrant 72. One may start from the sclera, counterclockwise. If there is no obscuration, discontinuity or the like, then a break point may be defined between the first and second quadrants as noted in step 1. If there is no obscuration, discontinuity or the like, then a break point may be defined between the first and second quadrants. The statements in box 76 may be used as indicated herein.



  
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          else
        
        
          
            
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                TR
              
            
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    .
  



Step 3 may include an interpolation/mask test. The statements as stated in box 77 may be used as indicated herein.

if (|θTR−θTLλ′|)mask(:,θTL:θTR)=1

elselinear interpolation

Steps 4 and 5 use the same statements as steps 1 and 2 except quadrants TL 71 and TR 72 may be substituted with quadrants BL 73 and BR 74, respectively. The same substitution may apply for step 6 in lieu of step 3. Full segmentation (i.e., no masking) may be used. Full segmentation is equivalent to a single point interpolation.
One may start at 0 degrees with respect to the x axis (x-axis may change based upon head tilting and is always assumed to be the normal of the head orientation, that passes by the two eye centers; y-axis is the normal direction of the x-axis that defines the head orientation) in the left quadrant and move out to a break point. When the break point is encountered, then that portion of the quadrant may become TL. Generally the break point will be a discontinuity such as an eyelash. If there is no break point, the edges of POSE are preserved (as good edges) and process is completed toward specified limits. The low left and right quadrants may be handled similarly.
In the quadrant pairs TL and TR and BL and BR, the break points may not exist in case of an open eye with no eye lid obscurations. The POSE edges are applicable as captured by original algorithm POSE. An obscuration between the break points may determine an angle between the break points. An angle θo may be determined as an interpolation, i.e., a line between the break points. If there is a large angle, then both quadrants, i.e., TL and TR, may be blocked with masking. For example, an angle of 100 degrees may leave little iris left in the two quadrants.
FIG. 8 is a graph 78 of histogram data versus intensity values for typical pixel distributions. One may discriminate between iris and non-iris pixels by clustering pixel distributions. This process relates to map analysis involving a stage for extracting outliers in the iris map. The may be clusters 37 and 38 of pixels outliers. Cluster 37 may be set out by valleys 39 and 79 in the histogram 78. The iris pixels should be part of just one cluster as the color of the iris would tend to result in pixels having a similar intensity since there is generally one overall color in the iris. Cluster 37 appears to be the one with the iris pixels. Cluster 38 would then be noise such a blocked lower portion of the iris or a bright reflective spot on the iris which may be regarded as an outlier. Such portion may be masked out in an iris map. Additional filtering may be considered at the feature extraction stage to clean up outliers from the iris map. There may be no need to add another segmentation process in the lower lid segmentation.
There may be leaked pixels from a cluster to another due to poor segmentation or other artifacts, e.g., reflections. Thus searching for the valley points among cluster may result in misplacement of the actual limits of the clusters. Thus one may impose limitations on the extent of valley searches by guaranteeing at least 90 percent of the iris pixels to be within the iris cluster. FIG. 9 shows an extension of intensity ranges associated with the imposed limits and a statement (i.e., formulas) of how to obtain these limits. There may be a certain percentage (e.g., 90 percent) of a distribution that covers a prominent cluster which likely represents the iris. An extraneous cluster outside the certain percentage of the distribution may represent noise subject to removal (10 percent expected percentage of noisy pixels).

{tilde over (x)}max=max(xσ, xλR)

{tilde over (x)}min=min(−xσ, xλL)

Such that




  
    
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          x
          σ
        
      
      
        x
        σ
      
    
    ⁢
    
      
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  >
  
    90
    ⁢
    %
  




Where λR and λL are the detected valleys in the right and left side of the iris pixel cluster. The cluster 37 of pixels represents the iris. Extraneous clusters 38 and 81 may be noted on both sides of cluster 37, separated by valleys 39 and 79, respectively. The iris map may be adaptively threshholded on the basis of intensity of the pixels. Assuming normal distribution, one would seek to keep 90 percent of the area of pixels including the main cluster 37. One may impose limits left and right at lines 82 and 83, respectively, or both to obtain at most 90 percent coverage. The 90 percent approach, although it could be another percentage especially if there is no valley or only one valley to separate or distinguish cluster 37, may guarantee enough area of the iris with cluster 37 for matching, analysis, identification, and/or the like. The remaining area is generally noise which may be removed.

FIG. 10 illustrates a multi-band (i.e., frequency) analysis with a showing of one, two and three banks 84 of code bits related to an iris. Each bank may have a filter and weighted appropriately in the matching process.
In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense.
Although the invention has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.

## Claims

1. A method for iris recognition comprising:
locating an eye with a camera;
obtaining an image of the eye with the camera;
assessing the image of the eye with a set of image quality metrics with a processor; and
segmenting the iris in the image of the eye with the processor;
wherein the set of image quality metrics comprises:
an offset measurement of the eye in the image of the eye; and
a gaze measurement of the eye in the image of the eye;

wherein a calibration of the segmenting of the iris is determined by the offset and gaze measurements; and
wherein:
if the offset and gaze measurements indicate offset or gaze of the eye in the image of the eye, then the segmenting of the iris is based on no circular calibration; and
if the offset and gaze measurements. indicate no offset or gaze of the eye, then the segmenting of the iris is based on circular calibration.

2. The method of claim 1, further comprising determining a quality score of the image of the eye with the set of image quality metrics with the processor.

3. The method of claim 2, further comprising:
determining a matching score of the image of the eye based on matches of the image of the eye with other images of the eye with the processor; and
establishing an evaluation score based on the quality score and the matching score with the processor.

4. The method of claim 1, wherein the set of image quality metrics further comprises:
a validity measurement of the image of the eye; and
a blur measurement of the image of the eye.

5. A method for iris recognition comprising:
locating an eye with a camera;
obtaining an image of the eye with the camera; and
assessing the image of the eye with a set of image quality metrics with a processor; and
segmenting the iris in the image of the eye with the processor;
wherein the set of image quality metrics comprises:
an offset measurement of the eye in the image of the eye; and
a gaze measurement of the eye in the image of the eye;

wherein a calibration of the segmenting of the iris is determined by the offset and gaze measurements;
wherein the set of image quality metrics further comprises:
an obscuration measurement of the eye in the image of the eye; and
a visibility measurement of the iris of the eye; and

wherein:
if the obscuration measurement of the eye reveals the eye not to be obscured, then a map of an iris of the eye is extracted with the processor; and
a visibility measurement of the iris in the map of the iris is made with the processor.

6. The method of claim 5, further comprising:
coding the iris in a single band code and/or multi-band code with associated weights based on the image quality metrics with the processor; and
matching the single band code and/or multi-band code with other codes of the iris with the processor.

7. The method of claim 6, wherein the set of image quality metrics further comprises:
a validity measurement of the image of the eye; and
a blur measurement of the image of the eye; and
wherein the associated weights based on the image quality metrics used in coding the iris are based at least in part on the blur measurement.

8. A method for iris recognition comprising:
locating an eye with a camera;
obtaining an image of the eye with the camera; and
assessing the image of the eye with a set of image quality metrics with a processor; and
segmenting the iris in the image of the eye with the processor;
wherein the set of image quality metrics comprises:
an offset measurement of the eye in the image of the eye; and
a gaze measurement of the eye in the image of the eye;

wherein a calibration of the segmenting of the iris is determined by the offset and gaze measurements; and
wherein segmenting the iris includes a quadrant iris analysis performed with the processor, the quadrant iris analysis comprising:
finding a first limit in a first quadrant toward a second quadrant, starting from a sclera in a first direction;
finding a second limit in newly defined second quadrant based on the first limit, starting from the sclera at the horizontal axis in a second direction opposite the first direction;
applying an interpolation/mask test to the first and second quadrants;
finding limits in a third quadrant in a direction toward a fourth quadrant;
finding limits in a newly defined fourth quadrant in an opposite direction; and
applying an interpolation/mask test to the third and fourth quadrants.

9. A system for iris recognition using quality metrics, comprising:
an eye image source;
a quality metric mechanism connected to the eye image source;
an iris map extractor connected to the quality metric mechanism and configured to extract a map of an iris; and
a processor configured to eliminate intensity outliers in the map;
wherein clustering pixel intensities of the map is based on their distributed histogram by selectively choosing limits of the iris as represented in the map using associated valleys on the left and right of an iris pixel cluster.

10. A system for iris recognition using quality metrics, comprising:
an eye image source;
a quality metric mechanism connected to the eye image source; and an iris map extractor connected to the quality metric mechanism and configured to extract a map of an iris;
wherein:
a limited range is imposed to preserve a certain percentage of pixel elements of a prominent pixel cluster which likely represents the iris in the map; and
an element beyond the limited range or the estimated thresholds of the pixel cluster represents noise subject to removal.