SWIR Imaging for Facial Image Capture through Tinted

Transcription

SWIR Imaging for Facial Image Capture through Tinted Materials
Jason Ice, Neeru Narang, Cameron Whitelam, Nathan Kalka, Larry Hornak1, Jeremy Dawson, and
Thirimachos Bourlai
Lane Department of Computer Science and Electrical Engineering, West Virginia University,
Morgantown, WV 26506
ABSTRACT
The use of short wave infrared (SWIR) imaging and illumination technology is at the forefront of system development
for military and law enforcement in both night and daytime operational scenarios1 2 3 4. Along with enabling nighttime
operations, a secondary benefit of SWIR imaging is that it offers the possibility to capture images through tinted
materials, such as tinted architectural or automotive glass and sunglass lenses5. The use of SWIR technology introduces
challenges to facial recognition when comparing cross-spectrally from a visible gallery to images captured in the SWIR6.
The challenges of SWIR facial recognition are further compounded by the presence of tinted materials in the imaging
path due to varying material types, lighting conditions, and viewing angle.
The paper discusses material and optical characterization efforts undertaken to understand the effects of temperature,
interior and exterior light sources, and viewing angle on the quality of facial images captured through tinted materials.
Temperature vs. spectrum curves are shown for tinted architectural, automotive, and sunglass materials over the range of
-10 to 55C. The results of imaging under various permutations of interior and exterior lighting, along with viewing
angle, are used to evaluate the efficacy of eye detection for cross-spectral facial recognition under these conditions.
Keywords: SWIR, facial recognition, eye detection, tinted materials, night vision, infrared, imaging, cross-spectral
1. INTRODUCTION
A wide variety of face recognition (FR) systems utilize image capture techniques within the visible range of the
electromagnetic spectrum (380 – 750 nm)7. However, most of these visible-spectrum FR systems rely upon favorable
and relatively consistent environmental variables, such as: adequate lighting, predictable weather patterns, and optimum
visibility of the individual or group of individuals8. These uncontrollable variables impose significant challenges to
facial recognition in real-time battlefield and law enforcement scenarios9 10. In order for FR systems to acquire useful
information from facial imagery in challenging scenarios, special emphasis has been placed in the short wave infrared
(SWIR) spectrum spanning from 950 to 1700 nm11 12. Facial recognition systems that can overcome the coupled
challenges of tinted materials and uncontrollable environmental variables, such as temperature and lighting levels, can
provide government and law enforcement agencies increased security and reliability in identification scenarios.
In addition to integrating SWIR technology with current FR setups to enable cross-spectral (i.e. SWIR to visible or vice
versa) imaging in difficult environments, a great deal of attention has been placed on identification of individuals when
imaged through obstructive mediums, such as tinted car windows or light-reflective architectural glass panels found on
many buildings. The benefits of SWIR imaging coupled with images from the visible spectrum will allow for successful
eye detection for facial recognition through optical materials. These benefits include: higher tolerance to low-level
obscurants (i.e. fog and smoke) than near infrared (NIR) imagery, the ability to reveal additional image characteristics
not always particularly found in other IR band counterparts (i.e. skin reflectance information of individuals from
different ethnic groups), and utilizing existing infrared light illumination in the surrounding environment, either natural
or man-made (i.e. indoor/outdoor light appliances, sunlight, moonlight, or starlight)13 14 15.
Understanding how varying environmental factors can alter the overall quality of a facial image through tinted/reflective
materials is essential in order to enable facial recognition in any given scenario that SWIR FR systems may encounter in
1
Participated as part of the National Science Foundation Independent Research/Development Program
Infrared Technology and Applications XXXVIII, edited by Bjørn F. Andresen, Gabor F. Fulop, Paul R. Norton,
Proc. of SPIE Vol. 8353, 83530S · © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.919105
Proc. of SPIE Vol. 8353 83530S-1
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real-time. This includes rapid temperature fluctuation, visibility changes from transparent to tinted/mirror-coated
mediums, lighting variations, etc. Our group has investigated how each of these factors may affect overall image results
obtained in the visible and SWIR bands. In addition, methods of minimizing the negative impacts of these environmental
variables have been developed.
1.1 Preliminary Cross-Spectral Imaging Results
In previous studies at West Virginia University, the SWIR band was studied in order to illustrate the advantages and
limitations of SWIR face verification, which included assembling a database of 50 subjects to demonstrate the
challenges associated with face verification and designing a set of experiments to highlight the possibilities of SWIR
cross-spectral matching14. These experiments showed that images captured under different SWIR wavelengths, ranging
from 950 – 1550 nm, can be matched to visible images with promising results. The role of multispectral fusion in
improving recognition performance in SWIR images was also illustrated14. Additional studies were performed in
multispectral eye detection to illustrate its own set of advantages and limitations of multi-band eye localization in the
visible, multispectral, and SWIR bands16.
In addition to these findings, further research included enhanced details regarding extraction, processing and matching of
facial/eye imaging under adverse night conditions in the presence of either available natural or artificial illumination17.
Spectral ranges including visible, near infrared (NIR), mid wave infrared (MWIR), and long wave infrared (LWIR)
wavelengths were examined in terms of night vision performance and illumination ranges of operational interest17. The
results from this study served as a foundation for future studies regarding how biometrics is utilized in difficult
environments, including this research paper. Another study conducted shortly afterwards demonstrated matching short
wave infrared (SWIR) face images to visible images acquired in fully controlled (indoors), semi-controlled (indoors at
standoff distances ≥ 50m), and uncontrolled (outdoor operational conditions) environments18.
Based on these findings, as well as research conducted by other research groups, the next phase of our research involves
cross-spectral eye detection for face recognition in challenging environments when visibility of an individual is
obstructed by tinted/reflective component(s).
1.2 Paper Organization
Based on preliminary results from previous studies, outdoor temperature and different combinations of interior and
exterior lighting appear to be critical factors that impact image quality in real time FR systems. As a result, this study
focuses on an evaluation of these conditions when glass panels and sunglasses act as facial obscurants to observe their
impact upon cross-spectral imaging in the visible and SWIR bands. The sections of this paper are organized as follows.
Section 2 provides an overview on how temperature change affects optical transparency of various glass and plastic
materials. Section 3 highlights how lighting variations impact the visibility of an individual through a variety of
mediums from transparent to tinted/mirror-coated. Section 4 briefly summarizes our research findings on cross-spectral
imaging of individuals through various materials in challenging environments and the future direction of this research.
2. TINTED MATERIAL CHARACTERIZATION
The purpose of this study was to measure the transmission spectrum of various types of tinted glass and eyewear plastics
across a temperature range of ~-10°C to ~55°C and spectral range between 350nm and 1700nm to determine if there
were any wavelength-specific transmissivity regions for these materials across this temperature range. These regions
could impact SWIR imaging of faces and/or irides through these materials if specific wavelengths experience severe
attenuation due to material temperature change. This study was accomplished in two stages for each material sample.
In the first stage, the sample was removed from a freezer and allowed to warm up to room temperature while the
transmission spectrum was monitored using a dual visible-SWIR interferometer setup (Fig. 1).
(a))
(bb)
Figuree 1: Glass characcterization setup (a) Technical deesign, (b) Constrructed workspacce.
In the secondd stage, the sam
mple was removed from an oven and allow
wed to cool to room temperaature while moonitoring
the transmisssion spectrum. Max heating temperature
t
waas 54°C for thee solid glass paanels and 43°C for the sunglaasses and
film-tinted saamples (to avo
oid melting). Thhe light sourcee used for testinng was a calibrrated tungsten halogen source (B&W
Tek BPS120-CC) with specctral range from
m 350 nm to 2600 nm. The normalized
n
outpput spectrum for
fo this device is
i shown
in Fig. 2.
Figure 2: Ligght source outputt spectrum from B&W Tek BPS
S120-CC.
The materiall samples used in this study represent
r
comm
mon architectuural and automootive tinted glaass with tint em
mbedded
in the materrial (2 architecctural samples with mirror coating),
c
clearr plate glass coovered with tiinted plastic film,
fi
and
various typess of eyewear plastic.
p
Table 1 provides a liist of the mateerials used in thhis study. Durring data collecction for
each sample,, the transmisssion spectrum was measuredd from wavelenngths betweenn 350nm and 1700nm
1
using a B&W
Tek BRC1122E-V and BTC
C261E-512-L visible
v
and SW
WIR spectromeeters, respectivvely. The transsmission spectrrum was
recorded at 2-4°C
2
intervalss using a Flukee 561 non-conttact thermometter. This intervval varied depeending on the speed of
heating/cooliing of the samp
ple (size/thicknness dependentt).
Table 1: Lisst of materials ussed for the charaacterization expeeriment.
(a)
(b)
(c)
(d)
Figure 3: Visible/SWIR spectra vs. relative intensity plots for: (a) Graylite II Architectural Glass, (b) Vista Gray
Automotive Glass, (c) Clear Glass w/ 80% Film Tint, and (d) Oakley Flak Jacket Sunglasses.
(a)
(b)
(c)
(d)
Figure 4: Frozen/Heated spectra vs. relative intensity plots for: (a) Graylite II Architectural Glass, (b) Vista Gray
Automotive Glass, (c) Clear Glass w/ 80% Film Tint, and (d) Oakley Flak Jacket Sunglasses.
As observed in the data for the architectural glass (Fig. 3 (a) and Fig. 4 (a)), there is no measurable dip or spike in
intensity vs. temperature for any specific wavelength. However, there is a measurable change in relative intensity for all
wavelengths. This behavior primarily occurs for the frozen glass samples. Upon removal from the freezer, frost
immediately forms on the glass, followed by condensation that remains on most of the glass area until room temperature
(Fig. 5). This causes a large decrease in transmitted intensity across all frequencies due to the frosting, and a peak higher
than the baseline of the heated glass samples just after thawing, most likely due to light scattering effects of the ice and
moisture.
Figure 5: Frosting (left) andd condensation (right)
(
on low-teemperature glass due to room hum
midity.
The results for
f the automo
otive glass (Figg. 3 (b) and Fig. 4 (b)) are consistent withh what was seeen in the archhitectural
glass, with frrost formation at sub-zero tem
mperatures andd subsequent moisture
m
condennsation being the
t main mechaanism of
transmission variation at lo
ow temperaturees, and constannt transmissionn for high tempperatures. Whille the same cann be said
for the clear glass with film
m tint in that theere are no wavvelength-speciffic changes in transmission,
t
thhere is an oscilllation in
the transmisssion spectra forr all of these saamples that beggins around 7000 nm. This osccillation periodd varies with frrequency
and increasinng temperaturee (see Fig. 3 (c)) and Fig. 4 (c)). This signal artifact is mosst likely an effe
fect of the thin film tint
on the clear glass panel caausing varying transmittance as wavelengthh and thicknesss (depended on
o temperaturee) varies,
acting as a noon-optimized anti-reflection/t
a
transmission coating.
While the daata from the sun
nglasses (Fig. 3 (d) and Fig. 4 (d)) shows data
d trends sim
milar to the glasss panels, theree is often
a large degreee of intensity variability
v
betw
ween the visiblle and SWIR spectra.
s
Again, this is mainlyy due to frost foormation
and condensation at low teemperatures. In addition, thee curved surfaace of the lensees created a high angular vaariability
when switching from the frozen
fr
measureements to the heated
h
measureements. The thhermal mass off the lenses waas low as
well, makingg it difficult to record
r
the specctra for fine tem
mperature channges.
(a)
(b)
Figu
ure 6: Constructted sunglasses setup (a) Capturiing the optical inntensity of our tungsten
t
light soource through a
pair of sunglasses, (b
b) Top view of the
t curved surfacce for a pair of sunglasses.
s
3. TRANSPARE
T
ENCY EVAL
LUATION OF
O TINTED MATERIAL
M
LS
After compleetion of the characterization phase
p
for our materials,
m
we began
b
to evaluuate the lightingg conditions needed to
perform optical characterizzation studies that
t
would be used in a futuure small scale--data collectionn. Because it has
h been
observed in preliminary studies that inteerior light sourrces play an im
mportant role in
i imaging thrrough tinted gllass, this
parameter waas evaluated firrst.
A series of images
i
were taaken in both visible
v
and SW
WIR spectra at 2m
2 standoff distances througgh three glass samples
used in the previous
p
materrial characterizzation experim
ment: Optigray 23, Graylite II,
I and Solarcoool (2) Graylitee. These
samples provvide a represen
ntative level off light, medium
m and dark tinnt (with mirror coating), resppective to listinng order.
The sampless were mounteed on the glasss collection boooth, and the subject particiipated in the experiment
e
waas seated
inside the boooth were diffeerent lighting conditions
c
werre tested. The interior 2-poinnt tungsten ligghting was variied from
full intensityy (measured at ~2600 lux), doown to half inteensity (~1300 lux), and quartter intensity (~
~650 lux). Imagges were
captured undder the followin
ng conditions:
1.
Befo
fore and after using
u
glass paneels of differentt intensity levels
2.
Befo
fore and after the
t subject was holding a coolor calibrationn card. When thhe subject wass not holding the
t card,
full frontal face im
mages were acqquired
An InGaAs-bbased Goodrich
h SU640HSX--1.7RT SWIR camera
c
was chhosen for imagee acquisition based
b
on previoous work
in this area199 20. The solid-sstate InGaAs imaging
i
array possesses
p
highh sensitivity in the 900 – 17000 nm spectrum
m, and is
capable of caapturing imagees at 640x512 pixel resolutioon. We observeed that the quaality of SWIR images
i
captureed under
these conditiions, in terms of
o contrast andd visibility of the
t face imagees acquired behhind glass, is well
w enough foor all tint
levels, even at 1/4th of thee interior lightiing level. Cam
mera integrationn time was adj
djusted so as noot to create siggnificant
motion blur in
i video captu
ure. An observaable reduction in the image contrast
c
of the SWIR imagess were seen in all three
lighting scennarios for each set of images captured,
c
especcially for the daarker tints.
Table 2: Visible and SWIR images
i
capturedd at full, half, andd quarter intensitty with Graylite II glass.
Graylite II (medium tint)) at Full, Half, annd Quarter Intennsity
Fulll Intensity (~26000 lux)
Half Intensity (~1300 lux)
Quarter Intensity
I
(~650 lux)
l
Visible
SWIR
Using collected data from various particiipants under thhese conditionss, we extendedd the experimeent by incorporrating an
c
in ordder to evaluatee the transpareency of each material
m
sample (tinted
image qualitty measure, naamely image contrast,
glasses and sunglasses).
s
To
o accurately exaamine these paarameters, eachh subject perforrmed the follow
wing actions:
1.
Thee participant is holding a color chart that hass standardized grayscale valuues
2.
Thee participant’s face was captuured when usinng 17 glass paanels and 7 sunnglass types pllaced between his face
and the two camerras used, i.e., one
o visible and one SWIR
The SWIR-bband images weere obtained ussing custom-m
made bandpass filters from Anndover Corporaation, with peaak center
frequency traansmission waavelengths of 1150, 1250, 1350, 1450, and 1550 nm, each having a 1000 nm pass bannd. Thus,
for each scennario, seven saample images were
w
acquired. During the abbove process thhe following ligghting conditioons were
used:
•
Glass panels – full interior and exterior lighting
•
Sunglasses – full interior, no exterior lighting (exterior lighting caused too much glare on the lenses due to the
short standoff distance)
For each SWIR sample image acquired under the aforementioned data collection scenarios, a numerical value was
computed representing the image graininess (or Contrast Quality Measure - CQM). Graininess is measured by the
percentage change in image contrast of the original image before and after blurring is applied. This measure can provide
quantitative information on the transparency level of each material sample, viz., how the image contrast changes with
tint level.
Four different regions from each image sample acquired under both of the data collection scenarios used were selected
for evaluation based on their graininess level:
•
Region 1 - Color chart grayscale area
•
Region 2 - Skin of the individual
•
Region 3 - Background
•
Region 4 - Left eye region (in this case, the large front panel of the collection booth was removed in order to
achieve the best image quality)
Figure 7: Sample of images used for the contrast study: (a) Glass panel image (visible spectrum); (b) Subject
wearing sunglasses (visible spectrum); (c) Glass panel SWIR image; (d) Subject wearing sunglasses (SWIR
spectrum). The four regions of interest are also highlighted.
Table 3: Sample cropped regions for image contrast study (glass panels).
Sample Cropped Regions For Image Contrast Study (Glass Panels)
No Glass
Color Chart
(Clear w/ 85%
Film Tint)
No Glass
Background
(Clear w/ 85%
Film Tint)
No Glass
Skin (Clear w/
85% Film Tint)
CQM: 0.559
CQM: 0.626
CQM: 0.344
CQM: 0.578
CQM: 0.293
CQM: 0.636
CQM: 0.613
CQM: 0.635
CQM: 0.432
CQM: 0.621
CQM: 0.574
CQM: 0.569
1150 nm
1550 nm
Table 4: Sample cropped eye region for image contrast study (sunglasses).
Sample Cropped Eye Region For Image Contrast Study (Sunglasses)
No Sunglasses
(Reference)
Oakley Flak Jacket
Oakley Straight
Jacket
RB3449 59
RB3025 58
CQM: 0.176
CQM: 0.212
CQM: 0.297
CQM: 0.205
CQM: 0.557
CQM: 0.338
CQM: 0.336
CQM: 0.373
CQM: 0.314
CQM: 0.612
1150 nm
1550 nm
All region 1 image portions used in this contrast study were cropped from the 3rd square from the left in the bottom row
(grayscale) of the color chart (see Fig. 7 (c)). Visual observation of the cropped sections of photos taken through the
glass sample indicates that, when using samples with increasingly darker tint, the darkness of the cropped images
(representing each ROI investigated) increase as well for wavelengths ranging from 1150 to 1550 nm. However, there
are a few exceptions to this observation in cases where reflections of bright objects appear in the dark glass panels.
These reflections of exterior objects resulted in degradation of the quality of the acquired images. In practice, the
observed reflection is the result of the darkness (high tint level) of the glass panel used in combination with the relative
difference of interior (within the booth) and exterior lighting levels. Similar observations can be made when using image
samples from regions 2 (background) and 3 (skin area).
Common obsservations wheen using images samples from
m the first threee regions with no
n reflections are:
(a) image
i
intensity
y appears unifoorm in each sam
mple image
(b) image
i
intensity
y appears consistent across eaach SWIR wavvelength
These obserrvations are qu
uantitatively confirmed
c
when using the CQM. For exxample, CQM
M is consistenntly high
(indicating loow contrast) in
n images acquiired at regionss 1 – 3. The onnly exceptions were when coomputing the CQM
C
on
sample images where reflecctions were preesent (as descrribed above), or
o on samples acquired
a
at regiion 4. In the laatter case
(see Table 4) the image co
ontrast is geneerally high, andd it becomes higher
h
in sampples with higheer visibility off the eye
regions. For example, wheen using the Seerengeti-Nuvinno sunglass typpe and the eyee region was caaptured at SW
WIR 1150
nm, CQM haas the lowest value (indicatinng high contrast). CQM resultts also show thhat image intennsity appears coonsistent
across each SWIR
S
wavelen
ngth. In order to justify this, we
w computed the
t standard deeviation (STD) of the CQM across
a
all
SWIR bandss on image sam
mples acquired in region 1 (ssee Fig. 7 and compare the visual
v
samples illustrated in Table
T
3).
We can see that
t
in cases where
w
reflectionns are present (e.g.,
(
when usiing the Solarcoool (2) Graylitee panel) STD becomes
b
very high. This
T
is becausee the CQM inn one particulaar wavelength was very low
w (high contrasst) due to pressence of
reflections.
Of particularr interest is the evaluation study
s
on sample images acquired from sunnglasses. A sm
maller croppedd area of
25x25 pixelss was used forr the sunglasses contrast stuudy in order too properly cappture the surfaace of one sidde of the
sunglasses without
w
includin
ng the frames of
o the sunglassses or unavoidaable light spotss on the lensess. The individuual's eyes
are noticeablle for every paair of sunglassses used exceppt the RB3025 58 due to thee dark embeddded tint and thhe mirror
coating on thhe lens, severelly minimizing visibility
v
of thee irises for bothh visible and SWIR
S
camera setups.
s
(a)
(b)
Figu
ure 8: (a) Standaard deviation off the CQM acrosss all SWIR bannds on image sam
mples acquired in
i region 1. We
can see that, when reflections
r
are present
p
(e.g., whhen using the Soolarcool (2) Graaylite panel), thee STD becomes
veryy high. This is beecause the CQM
M in one particullar wavelength was
w very low (hiigh contrast) duee to reflections.
(b) CQM
C
values thaat were computeed for image sam
mples (on variouus SWIR waveleengths) acquiredd at region 4 on
the reference
r
image (no sunglasses) and on images where
w
different sunglass
s
types were
w used.
The CQM vaalues from the glass panels were
w used, alongg with grayscalle and normalized transmission intensity vaalues (in
lux), to devellop a ranking the
t tinted glass materials from
m lightest to daarkest. The resuults are presentted in Table 5, with a
box plot of thhe grayscale vaalues shown inn Fig. 9. Figure 9 indicates thaat the solid glaass panels and clear
c
panels wiith
tinted film addded are well separated
s
in terrms of their basseline transmisssivity, offeringg a clear rankinng from 1 – 200 with no
overlap.
Table 5: Ranking of the tinted materials (glass panels and sunglasses) from lightest to darkest by comparing normalized
transmission intensity values (in lux). Highlighted materials were selected to be used in preliminary data collection.
Rank
Glass Panel
Rank
Glass Panel
Rank
Sunglasses
1
No Glass
11
Clear w/ 80% Film Tint
1
Oakley Flak Jacket
2
12
Optigray-23
2
Serengeti-Nuvino
3
Un-Tinted Glass Panel
(Clear w/ 0% Film Tint)
Solex (2.1mm)
13
3
RB3449 59
4
Solargreen C-5 (2.1mm)
14
Solarcool (2) Gray Reverse (mirror coating
inside booth)
GL-20 (3.9mm)
4
RB3217 62
5
Solargreen C-39 (2.1mm)
15
Solarcool (2) Gray
5
6
Solextra (2.1mm)
16
6
Oakley Straight
Jacket
RB3394
7
Vista Gray (3.9mm)
17
Graylite II
7
RB3025 58
8
Solargray
18
9
19
10
GL-35 (4.1mm)
20
Solarcool (2) Graylite Reverse (mirror coating
inside booth)
Solarcool (2) Graylite
Grayscale Value of White Color Chart Behind Various Glass Panels Using SWIR Camera w/ 1550 nm Filter
250
Grayscale Value
200
150
100
ra
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Figure 9: Box plot of grayscale values (0-255; averaged over 100x100 pixel area) for 1550 nm SWIR camera for all glass panels.
The tint transparency ranking was used to down-select the number of glass materials that will be used in the preliminary
data collection. Three samples were chosen representing low, medium, and dark tint (shaded fields in Table 5). Due to
interfering/obstructing reflections on the glass seen during initial testing using high exterior light levels at a short
imaging distance (2m), the camera setup was slightly angled (~12 deg.) to reduce the impact of reflections on images
captured under these lighting conditions. In addition, a neutral grey background was placed in the reflection path to
provide a constant background, further reducing the impact of image reflection. A schematic view of the data collection
setup is shown in Fig. 10.
Figure 10: Setup and lighting arrangement for preliminary data collection (not to scale).
The data collection parameters for this preliminary data collection are as follows:
•
•
•
Glass Panels:
o Un-Tinted Glass Panel (Clear w/ 0% Film Tint)
o Clear w/ 80% Film Tint
o Solarcool (2) Graylite
Cameras:
o Canon EOS 5D MARK II Camera; camera settings optimized for each lighting condition
o Goodrich InGaAs SWIR Camera; integration time (OPR) and on-board quality enhancement optimized for
each lighting condition; SWIR filters used: 1150 nm, 1250 nm, 1350 nm, 1450 nm, 1550 nm
Lighting Conditions:
o Full Exterior, Full Interior (for Ground Truth only)
o No Exterior, Full Interior
o No Exterior, Minimum Interior
o Full Exterior, No Interior
o Active SWIR Illumination
o Single-Source Exterior Lighting
As with the glass panels, multiple types of eyewear were subjected to a similar contrast and transparency study to down
select a representative subset of sunglasses for the data collection. After this study, the following sunglasses were
selected:
• Oakley Flak Jacket – lightest tint
• Oakley Straight Jacket – polarized
• RB3449 59 – two-tone tint
• RB3025 58 – darkest tint, mirror coating
The following is a brief description of each lighting condition with description of ‘full,’ ‘minimum’, and ‘no’ lighting
levels as measured at the participant seating location. The collection room was completely light controlled, with all
potential sources of light infiltration (doors, windows, etc.) ‘blacked-out’.
•
•
•
•
Interior Lighting: Two 250 W tungsten light bulbs inside the booth with position optimized to illuminate the
subject’s face without hot-spotting.
o Full: ~3.87 kilolux
o Minimum: ~60.2 lux
o No: ~0 lux
Exterior Lighting: Three-point tungsten lighting (500 W (x2; left & right), 250 W center)
o Full: ~352.2 lux
o No: ~0 lux
Active SWIR Illumination: 1550 nm laser source located outside booth with diffused 500 mW output to
eliminate hot-spotting
o Visible lux values should be ~0 lux (all tungsten lighting completely off)
Single-Source Exterior Lighting: One 250 W tungsten light bulb located ~6 meters away from the subject inside
the booth.
o ~5.2 lux
Table 6: Sample images for Clear w/ 80% Film Tint Glass Panel.
Subject Under Various Lighting Conditions Through Clear w/ 80% Film Tint Glass Panel
No Exterior, Full Interior
Lighting
Visible
1550 nm
Visible
Full Exterior, No Interior
Lighting
Visible
1550 nm
1150 nm
1250 nm
1350 nm
No
Exterior,
Minimum
Interior
Lighting
SingleSource
Exterior
Lighting
Active SWIR Illumination
Visible
1450 nm
1550 nm
1550 nm
Table 7: Sample images for Oakley Flak Jacket Sunglasses.
Subject Under Various Lighting Conditions Wearing Oakley Flak Jacket Sunglasses
Visible
1150 nm
1250 nm
1350 nm
1450 nm
1550 nm
Full Exterior,
No Interior
Lighting
SingleSource
Exterior
Lighting
Active SWIR
Illumination
This preliminary data analysis indicates that when operating in the SWIR band, glass transparency is higher than when
operating in the visible spectrum. Another important observation is that glass transparency decreases with increasing
SWIR wavelength (see sample tables above). The only pair of sunglasses that transparency was not possible in either the
visible or SWIR spectrum (independent of the settings used) were the pair having the lowest normalized transmission
intensity value, i.e., Ray Ban - RB3025 58.
4. SUMMARY
We have presented a study on the problem of SWIR/visible cross-spectral facial recognition when individual(s) are
being observed through tinted materials at SWIR wavelengths ranging from 1150 – 1550 nm under varying temperature
and lighting conditions. Results from our preliminary studies have shown that temperature changes have minimal impact
upon spectral transmission through tinted/mirror-coated materials. The main issue is moisture condensation that can
occur due to rapid temperature change from freezing to room temperature, which causes a baseline decrease in
transmitted intensity across the whole wavelength range discussed. We developed a glass and sunglass tint transparency
ranking system to down-select the number of tint/mirror-coated materials that would be used in data collection effort, for
which 143 participants provided face images under various external/internal lighting conditions. Our findings suggest
that, overall, tinted material transparency in SWIR is higher than when operating in the visible spectrum, but visibility
gradually decreases with increasing wavelength from 1150 – 1550 nm. We also observed that, while minimal interior
lighting is sufficient to fully illuminate an individual’s facial features behind tinted materials for SWIR imaging, the
complete absence of interior lighting makes facial imaging challenging, especially in the case of high-intensity exterior
sources that cause significant reflection.
The next phase of our research will be to develop additional methods of minimalizing image quality-degrading factors
for the most challenging glass and sunglass samples, and organize a large-scale data collection of ~200 individuals
undergoing similar scenarios previously demonstrated in our preliminary data collection. These images will be used to
demonstrate eye detection and facial restoration algorithms upon individuals obstructed by optical components in realtime environments for illustrating improvements in cross-spectral facial recognition.
5. ACKNOWLEDGEMENTS
This work is sponsored in part through a grant from the Office of Naval Research, contract N00014-09-C-0495, and
support from the NSF Center for Identification Technology Research (CITeR), award number IIP-0641331. The authors
are grateful to Simona Crihalmeanu, Arvind Jagannathan, Nnamdi Osia, Michael Lyons, Kyle Smith, and Lucas Rider
for their assistance in the data collection process.
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SWIR Imaging for Facial Image Capture through Tinted

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