Design of an Iris Im

Design of an Iris Im

Platform Platform

Philip D. Wasserman Philip D. Wasserman

Guest Researcher Guest Researcher

National Institute of Standa

National Institute of Standa

Gaithersburg MD Gaithersburg MD
Objectives Objectives

 Show how the imaging platform 

Show how the imaging platform 

recognition accuracy recognition accuracy

 Discuss components of the ima

Discuss components of the ima

platform platform

 Present design of NIST platform Present design of NIST platform Show images captured by NIST 

Show images captured by NIST 
Differing Error Rate R

Differing Error Rate R

 False Non False Non

-match Rate match Rate



[Daugman Daugman] no false non ] no false non

-matches 

matches 

comparisons comparisons

 [IBG] one false non [IBG] one false non

-match per 94.

match per 94.

comparisons comparisons

 False Match rate False Match rate



[Daugman Daugman] no errors in 9.21 millio

] no errors in 9.21 millio

 [IBG] one false match per 28,902 

[IBG] one false match per 28,902 

 IBG results are at the transacti IBG results are at the transaction level, same devic

on level, same devic

three devices three devices
Effects of imaging Platf

Distributions [Daugm

Poor Imaging Goo

“Genuines” distribution (on left) varies greatly with ima

affects FNMR

“Imposters” distribution (on right) is largely independe

affects (FMR) 

Reproduced with the permission of Dr. John Daugman
Plan

 Image platform affects iris accuracy Image platform affects iris accuracy No quantified data that identifies ef

No quantified data that identifies ef

different imaging defects different imaging defects

 NIST imaging platform will produce 

NIST imaging platform will produce 

 images of sufficient quality to achieve 

images of sufficient quality to achieve 

potential of algorithms potential of algorithms

 Imaging defects can be introduced, on

Imaging defects can be introduced, on

quantify the effects of each quantify the effects of each

• Separately Separately• In combination In combination 
Components of an Iris 

Components of an Iris 

Platform Platform

 Digital Image Sensor Digital Image Sensor Lens Illuminator Illuminator Camera Subject interface Subject interface
Digital Image Se

Digital Image Se
Digital Image Sen

Digital Image Sen

 Converts image to digital form Converts image to digital form CCD or CMOS CCD or CMOS Sensor must not have IR, Colo

Sensor must not have IR, Colo

aliasing filters aliasing filters
Digital Image Sensor 

Digital Image Sensor 

 Sensor size affects resolution Sensor size affects resolution

 Analogous to advantage of large film size Analogous to advantage of large film size

 Pixel size affects dynamic range Pixel size affects dynamic range

 Large pixels capture more Large pixels capture more light, decreasing no

 light, decreasing n

 Pixels smaller than the diffracti Pixels smaller than the diffraction limit do not 

on limit do not 

 Defective pixels: inevitable with solid Defective pixels: inevitable with solid

-stat

stat

 always black always black always white always white “lazy pixels”, sensitivity differences “lazy pixels”, sensitivity differences number and maximum cluster size must be sp

number and maximum cluster size must be sp

 Modern cameras compensate for these Modern cameras compensate for these
Digital Image Sensor (

Digital Image Sensor (

 Solid state sensors: CCD or CMOS Solid state sensors: CCD or CMOS

 CCDs have been the choice for low noise CCDs have been the choice for low noise CMOS sensors are approaching the performa

CMOS sensors are approaching the performa

 Number of pixels does not fully define res

Number of pixels does not fully define res

 Pixel spacing controls spatial sampling rate Pixel spacing controls spatial sampling rate

• Aliasing Aliasing • Nyquist limit Nyquist limit

 Pixel

-pixel crosstalk reduces resolution pixel crosstalk reduces resolution

• Acts as low pass filter on image Acts as low pass filter on image

 Sensor may have built Sensor may have built

-in filters that make it i

in filters that make it 

NIR (Near Infrared) imaging NIR (Near Infrared) imaging

• RGB• Anti-aliasing (low aliasing (low-pass)

 Sensor spectral sensitivity must extend in

Sensor spectral sensitivity must extend in
Important Digital Image 

Important Digital Image 

Specifications Specifications

 Dynamic Range Dynamic Range

 = 20 log (Max Output (p = 20 log (Max Output (p-p) / Read Noise (rms)) p) / Read Noise (rms))

 Fixed pattern noise (FPN) Fixed pattern noise (FPN)

 = Fixed pixel = Fixed pixel-pixel offset variations pixel offset variations

 Photo Response Non Photo Response Non

-Uniformity (PRNU) Uniformity (PRNU) 

 = Fixed pixel = Fixed pixel-pixel gain variations pixel gain variations

 Responsivity Responsivity

 = Output in digital numbers / light input in nJ/cm

2

 Read Noise Read Noise

 = Random rms noise of the digital output = Random rms noise of the digital output

 Noise Equivalent Exposure Noise Equivalent Exposure

 Read Noise / Responsivity Read Noise / Responsivity

 Saturation Equivalent Exposure (NEE) Saturation Equivalent Exposure (NEE)

 = Maximum Output /Responsivity = Maximum Output /Responsivity
Lens
Lens

 The lens must project an accura

The lens must project an accura

the subject onto the digital senso

the subject onto the digital sens

 NIR digital imaging places spec

NIR digital imaging places spec

requirements on the lens requirements on the lens 

 Design must be optimized for the 

Design must be optimized for the 

 Coatings must reduce reflections i

Coatings must reduce reflections 

 Optical design must include senso

Optical design must include senso
NIR Lens Requirem

NIR Lens Requirem

 Lens must be optimized for low aberratio

Lens must be optimized for low aberratio

 Lens coatings must be designed for the N

Lens coatings must be designed for the N

 Lens elements are coated to reduc Lens elements are coated to reduce reflection

e reflection

loss of approximately 4.0 loss of approximately 4.0 

– 5.0% at each surfa

5.0% at each surfa

• 10 

– 20 surfaces are common 20 surfaces are common

• NIR optimized coatings will reduce loss to 0.5 NIR optimized coatings will reduce loss to 0.5-

 Lens coatings not optimized for the NIR will ca

Lens coatings not optimized for the NIR will c

• light loss light loss

• internal reflections internal reflections• ghost images ghost images

 Broad

-band lenses cover both the NIR an

band lenses cover both the NIR an

 Lens must be designed for digital sensor 

Lens must be designed for digital sensor 

 Cover glass on sensor must Cover glass on sensor must be included in len

be included in len

 Small pixel sizes (3 Small pixel sizes (3

-12 microns) increase requ

12 microns) increase requ

quality. quality.
AR (Anti AR (Anti-reflective) C

reflective) C

Courtesy of Edmund Optics
Measures of Lens Q

Measures of Lens Q

 Image Sharpness Image Sharpness Distortion level Distortion level Uniformity of light distribution Uniformity of light distribution
Image Sharpnes

Image Sharpnes

 Lack of sharpness has several 

Lack of sharpness has several 

 Focus error Focus error Diffraction Diffraction Lens aberrations Lens aberrations Sensor spatial sampling rate Sensor spatial sampling rate Sensor pixel crosstalk Sensor pixel crosstalk Subject motion Subject motion

 Overall Image sharpness can e

Overall Image sharpness can e

as MTF (Modulation Transfer F

(Modulation Transfer F
Depth of Field Curv

Depth of Field Curv

Depth of field is the distance range ove

image is deemed in-focus
DOF Formula

DOF = range over which 

in focus

 DOF =

c * N * (1+M/p) / (M^2 * (1 c * N * (1+M/p) / (M^2 * (1 

± (N * c) / (f * M

(N * c) / (f * 

Use + for front DOF, Use + for front DOF, 

- for rear DOF for rear DOF

 Where:

c = diameter of largest acce c = diameter of largest acceptable circle o

ptable circle o

N = f

-number

M = magnification M = magnificationp = pupil magnification p = pupil magnification f = focal length of lens f = focal length of lens
Diffraction Diffraction

 Diffraction imposes a fundamental 

Diffraction imposes a fundamental 

on image sharpness on image sharpness

 A point source of light passing through 

A point source of light passing through 

produces a diffraction pattern of altern

produces a diffraction pattern of altern

dark concentric rings. dark concentric rings.

 Called an Called an Airy disk Airy disk

 Radius, R, of the Airy disk from pe

Radius, R, of the Airy disk from pe

minimum varies directly as the f minimum varies directly as the f-nu

nu

wavelength wavelength

 R = 1.22 * wavelength * f R = 1.22 * wavelength * f-number N.A. is equivalent measure: N.A. = 1 / 

N.A. is equivalent measure: N.A. = 1 / 

 Airy Disk Simulation (Nikon) Airy Disk Simulation (Nikon)
Lens Resolution and f Lens Resolution and f

-

 Lenses are usually aberration limite

Lenses are usually aberration limite

numbers numbers 

 At high f At high f

-numbers, lens resolution b

numbers, lens resolution b

diffraction limited. diffraction limited.

 In the NIR, due to longer wavelengt

In the NIR, due to longer wavelengt

results in almost a 40% reduction in 

results in almost a 40% reduction in 

relative to visible light. relative to visible light.
Quantifying Sharpness Us

Quantifying Sharpness Us

 Traditional method of measuring MTF is 

Traditional method of measuring MTF is 

observation of a resolution chart image. observation of a resolution chart image. 

 value is subjective value is subjective typically yields optimistic MTF at about 2 typically yields optimistic MTF at about 2

-5% m

5% 

 MTF can be objectively me MTF can be objectively measured using t

asured using 

edge method. edge method.

 Requires an image with a sharp, Requires an image with a sharp, slanted dark

slanted dark

suitable software [Imatest] suitable software [Imatest]

 ISO 12233:2000 Photography ISO 12233:2000 Photography 

-Electronic still 

Electronic still 

Resolution measurements Resolution measurements 

 Complete MTF specification must include 

Complete MTF specification must include 

level, a wavelength wavelength, and overshoot lim

overshoot lim

 MTF at 60%, 840nm, is 4 line MTF at 60%, 840nm, is 4 line

-pairs/mm with 

pairs/mm with 

overshoot less than 10%

 MTF50 = MTF50 = lp/mm at 50% modulation /mm at 50% modulation

 0.38 /(Wavelength * f 0.38 /(Wavelength * f

-Number) Number)

Sloping Edge Resolutio

Sloping Edge Resolutio

MagnFOV = WaveMTF6
Digital Signal Process

Digital Signal Process

Image

 MTF can be increased by digita

MTF can be increased by digita

sharpening. sharpening.

 Excessive sharpening will prod

Excessive sharpening will prod

overshoot or ringing on edges. overshoot or ringing on edges.

 Edge profile will show this disto

Edge profile will show this disto

 The edge profile can be produc

The edge profile can be produc

commercial software [Imatest]. commercial software [Imatest].
Lens Aberration

Lens Aberration

 Aberrations are deviations from 

Aberrations are deviations from 

lens

 Every lens has aberrations Every lens has aberrations

 The lens designer uses multiple o

The lens designer uses multiple o

elements to reduce aberrations. elements to reduce aberrations.
Common Lens Aberr

Common Lens Aberr

Illustrations courtesy of Dr. Rod Nave Illustrations courtesy of Dr. Rod Nave

Department of Physics and Astronomy Department of Physics and Astronomy Georgia State University Georgia State University Atlanta, GA 30303 Atlanta, GA 30303-3083 
Chromatic Aberrat

Chromatic Aberrat

Light of Different Wave

Light of Different Wave

Focus at Different Dist

Focus at Different Dist
Distortion Distortion
Curvature of Fie

Curvature of Fie
Spherical Aberratio

Spherical Aberratio

Rays Focus at Different Distances De

Rays Focus at Different Distances De

Position on Lens Position on Lens
Astigmatism Astigmatism
Calculated Optical Chara

Calculated Optical Chara

 focal length in mm: 16.4 focal length in mm: 16.4 f-number: 8 number: 8 maximum permissible circle of confusion in mm : .07 maximum permissible circle of confusion in mm : .07 object width in mm: 120 object width in mm: 120 iris diameter in mm: 7 iris diameter in mm: 7 wavelength of illumination in NANOMETERS: 840 wavelength of illumination in NANOMETERS: 840 pupil magnification : 2.591 pupil magnification : 2.591 Height of field 96.1971 mm (3.78729 inches) Height of field 96.1971 mm (3.78729 inches) Horizontal pixels on iris = 175 Horizontal pixels on iris = 175 DIFFRACTION LIMITS DIFFRACTION LIMITS Rayleigh limit on sensor (from peak to first zero of airy 

Rayleigh limit on sensor (from peak to first zero of airy 

 Rayleigh limit on object: 93.696 microns Rayleigh limit on object: 93.696 microns Rayleigh MTF limit on sensor: 121.975 lp/mm Rayleigh MTF limit on object: 10.6728 lp/mm MTF50 on sensor 56.5476 MTF50 on sensor 56.5476 lp/mm MTF50 on object: 4.94792 MTF50 on object: 4.94792 lp/mm MTF60 on sensor: 48.631 MTF60 on sensor: 48.631 lp/mm MTF60 on object: 4.25521 MTF60 on object: 4.25521 lp/mm
Illuminator Illuminator
Illuminator Requirem

Illuminator Requirem

Uniform illumination over the are

Uniform illumination over the are

eye

 Sufficient intensity to maximize Sufficient intensity to maximize 

signal/noise ratio in sensor. signal/noise ratio in sensor.

 Wavelength range that produce

Wavelength range that produce

contrast of retinal features. contrast of retinal features.

 Levels of illumination that are s

Levels of illumination that are s

subject’s eye subject’s eye
Effects of Illuminat

Effects of Illuminat

Wavelength Wavelength

Brown Iris Blue Iris

http://

msp.pmit.edu.au
Illuminator Safe

Illuminator Safe

 High illumination levels can cause p

High illumination levels can cause p

eye damage eye damage

 NIR illumination is particularly hazardo

NIR illumination is particularly hazardo

 The eye does not respond with protec

The eye does not respond with protec

mechanisms (aversion, blinking, pupil 

mechanisms (aversion, blinking, pupil 

 Application requirements call for hig

Application requirements call for hig

 Depth of field strongly affects usability Depth of field strongly affects usability

• Typically achieved by increasing f Typically achieved by increasing f

-number

• Required light level increases as square o

Required light level increases as square o

 Short exposure time reduces motion a

Short exposure time reduces motion a

• Required light level varies inversely with e

Required light level varies inversely with e

 Signal/noise ratio is improved as light 

Signal/noise ratio is improved as light 
Structure of the Hum

Structure of the Hum
LED Eye Safety Stan

LED Eye Safety Stan

 See References See References

 [ACGIH] [ACGIH] [ICNIRP] [ICNIRP] [ICNIRP 2000] [ICNIRP 2000] [IEC] [ANSI]
Is This a Real Probl

Is This a Real Probl

 There is no reported case of retinal 

There is no reported case of retinal 

single LED. single LED.

 “Only because of the extraordinary 

“Only because of the extraordinary 

assumptions built into some current 

assumptions built into some curren

safety standards could one reach th

safety standards could one reach th

that an LED or IRED poses a safety 

that an LED or IRED poses a safety 

[ICNIRP 2000] [ICNIRP 2000]

 Multiple LED illuminators can easily 

Multiple LED illuminators can easily 

10/mw /cm 10/mw /cm2 safety limit safety limit

 Many illuminators use arrays of LEDs. Many illuminators use arrays of LEDs.

 New LED technologies are increasi

New LED technologies are increasi

brightness, so the situation bears w

brightness, so the situation bears w
Camera
The NIR Camer

The NIR Camer

 Interfaces sensor to computer Interfaces sensor to computer Controls image acquisition, display, a

Controls image acquisition, display, a

 Corrects for pixel Corrects for pixel

-pixel gain and offse

pixel gain and offse

 Must not have NIR block filter installe

Must not have NIR block filter installe

 NIR block filter is installed on nearly all 

NIR block filter is installed on nearly all 

cameras to reduce blurring from focal le

cameras to reduce blurring from focal le

differences between visible and NIR ligh

differences between visible and NIR ligh

 Must not have anti Must not have anti

-aliasing diffuser 

aliasing diffuser 

 Often used to avoid aliasing effects from 

Often used to avoid aliasing effects from 

sampling sampling
Subject Interfa

Subject Interfa
Subject Interfac

Subject Interfac

 Both eye and head position must b

Both eye and head position must b

 Cold mirror target with crosshairs Cold mirror target with crosshairs  Audible feedback Audible feedback Forehead and/or chin rest. Forehead and/or chin rest.

 Eye motion during exposure cause

Eye motion during exposure cause

blurring blurring

 Saccadic motion blur Saccadic motion blur

 eye moves approximately .001”, 60 tim

eye moves approximately .001”, 60 tim

 may limit image resolution may limit image resolution
NIST Iris Imagi

NIST Iris Imag

Platform Platform
Design Specificatio

Design Specificatio

 Captures two irises in a single 6.3 mega Captures two irises in a single 6.3 mega

-

image

 MTF60 (Modulation Transfer Function) greater 

(Modulation Transfer Function) greater 

840 nm with less than 10% 840 nm with less than 10% overshoot on edg

overshoot on edg

 Image distortion less than 2%

 Field of View (horizontal): 120mm Field of View (horizontal): 120mm Pixels on 7mm iris: 175 Pixels on 7mm iris: 175 Lens, camera, and cold mirror target opti

Lens, camera, and cold mirror target opt

(700

-900nm)

 Illuminator is eye Illuminator is eye

-safe at controlled dista

safe at controlled dista

 Rigid, accurate platform for stable optica

Rigid, accurate platform for stable optica

 Maximize use of COTS components Maximize use of COTS components  GUI user interface to view, capture, and 

GUI user interface to view, capture, and 

 Eye and Head position controlled Eye and Head position controlled

 Cold mirror eye target Cold mirror eye target Forehead rest Forehead rest

 Sustained image capture rate of 5 image

Sustained image capture rate of 5 image
Camera Specificatio

Camera Specificatio

 Pixelink PL Pixelink PL

-A 781

 Pixel count: 2208 x 3000 Pixel count: 2208 x 3000 Pixel pitch: 3.5 microns Pixel pitch: 3.5 microns Frame Rate 5 fps at 2208 x 3000 pixels Frame Rate 5 fps at 2208 x 3000 pixels

 Region of interest selection Region of interest selection

 Bit depth: 8 or 10 Bit depth: 8 or 10 Spectral Responsivity: > 4 DN (Digital Spectral Responsivity: > 4 DN (Digital Numbers)/(nJ/cm Numbers)/(nJ/cm

2

)

 FPN (Fixed Pattern Noise) < 1% (pixel FPN (Fixed Pattern Noise) < 1% (pixel

-pi

pi

 PRNU (Photo Response Non PRNU (Photo Response Non

-Uniformity)

Uniformity)

pixel gain) pixel gain)

 Each pixel is dynamically corrected for F

Each pixel is dynamically corrected for F

 Defective pixels are replaced with mean 

Defective pixels are replaced with mean 

pixels

 Read Noise < 1.4 digital numbers Read Noise < 1.4 digital numbers Dynamic Range: 56.7db Dynamic Range: 56.7db
Lens Specification

Lens Specification

 Schneider Cinegon 1.8/16 Schneider Cinegon 1.8/16 Broadband lens Broadband lens

 NIR corrected optics NIR corrected optics NIR lens coatings NIR lens coatings

 Distortion < 2% at maximum im

Distortion < 2% at maximum im

(10.5mm) (10.5mm)

 Relative illumination 60% at ma

Relative illumination 60% at ma

image extent image extent

 Modulation > 75% at 30 lp/mm

Modulation > 75% at 30 lp/mm
Illuminator Specificat

Illuminator Specificat

 Safe at controlled viewing dista

Safe at controlled viewing dista

 Less than 10mw/cm Less than 10mw/cm2 on subje

on subje

applicable safety specifications applicable safety specifications

 Eye illumination uniformity Eye illumination uniformity 

– 2% 

2% 

correction by camera) correction by camera) 

 840 nanometer center wavelen

840 nanometer center wavelen
Imaging Resu

Imaging Resu

Non

-enhanced image

enhanced image
Two Blue Eyes Two Blue Eyes
Single Blue Eye Single Blue Eye
Single Blue Eye Enh

Single Blue Eye Enh
Two Brown Eye

Two Brown Eye
One Brown Eye One Brown Eye
One Brown Eye Enha

One Brown Eye Enh
References References

 [Gamassi] M. Gamassi, et al, Accu [Gamassi] M. Gamassi, et al, Accuracy and Performance of B

racy and Performance of B

2004, 2004. 2004, 2004.

 [Daugman] John Daugman, [Daugman] John Daugman, How Iris Recognition Works How Iris Recognition Works [IBG] International Biometrics Group, [IBG] International Biometrics Group, Independent Testing of Independent Testing of 

Technology Final Report Technology Final Report, May 2005. , May 2005.

 [ACGIH] American Conference of Go [ACGIH] American Conference of Government Industr vernment Industrial Hyg

ial Hyg

Near Infra Near Infra-Red Illuminators”, 1981. Red Illuminators”, 1981.

 [ICNIRP 2000] “ICNIRP statement on light [ICNIRP 2000] “ICNIRP statement on light-emitting diodes (LE

emitting diodes (LE

Implications for Hazard Implications for Hazard Assessment”, Health Physics, Vol. 78

 Assessment”, Health Physics, Vol. 78

 [ICNIRP] International Commission on Non [ICNIRP] International Commission on Non-ionizing Radiatio

ionizing Radiatio

on Limits of Exposure to Broad on Limits of Exposure to Broad-Band Incoherent Optical Band Incoherent Optical Radi

Radi

1997.

 [IEC] 60825 [IEC] 60825-1 International Electrotechnical 1 International Electrotechnical Commission, “Sa

Commission, “Sa

Part1: Equipment classification, Part1: Equipment classification, requirements and user’s guid

 requirements and user’s guid

 [ANSI] American National Standar [ANSI] American National Standards Institute. “American Nat

ds Institute. “American Nat

safe use of lasers and LEDs used safe use of lasers and LEDs used in optical fiber transmission 

 in optical fiber transmission 

Laser Institute of America; ANSI Z136.2 1988 (2 Laser Institute of America; ANSI Z136.2 1988 (2nd edition,198

edition,198

 [CIE] Commission International [CIE] Commission International de l’Eclarirage. “Photobiologic

 de l’Eclarirage. “Photobiologic

lamps.” Vienna: CIE; Report of TC 6 lamps.” Vienna: CIE; Report of TC 6-38; CIE 134 38; CIE 134-3-99; 1999. 99; 1999.