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Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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POTENTIAL OF MULTISPECTRAL TECHNIQUES FOR MEASURING COLOR IN THE AUTOMOTIVE
SECTOR
Meritxell Vilaseca, Francisco J. Burgos,
Jaume Pujol
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Technological innovation center established in
1997 with the aim of structuring the activities in the
field of Optical Engineering (Terrassa Campus of
the Technical University of Catalonia).
http://www.cd6.upc.edu/
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Barcelona Vilanova i la Geltrú Castelldefels
Sant Cugat del Vallès
Terrassa
Manresa
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Visual optics and color group:
J. Pujol M. Vilaseca M. Arjona F. Díaz-Doutón S. Luque F. J. Burgos
M. Aldaba J. A. Herrera H. Zuluaga F. Sanabria J. C. Ondategui E. Ferrer A. Giner
Potential of multispectral and hyperspectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Outline
• Introduction
• What is a multispectral system?
• Components of multispectral systems
• Spectral sampling technique
• Calibrating a multispectral system
• Multispectral systems at the CD6
• Applications in the automotive sector
• Hyperspectral systems
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Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Standard instruments for color measurement:
spectroradiometers, spectrophotometers, colorimeters
Introduction
How color is measured?
• Cost (Diffraction grating)
• Integration of the viewing field
• Only one measurement simultaneously
• Slow speed
Potential of multispectral and hyperspectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Introduction
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High spatial resolution
Linearity
Rapid response
Acceptable SNR
High cuantum efficiency
Wide spectral range
Reduced size
Scientific image
Measurement instrument
with high spatial resolution
2. Color characterization
Instrument for color measurement
Is it possible to perform color measurements
using a digital camera?
1. Control and correction of the noise sources
Potential of multispectral and hyperspectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Introduction
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Is it possible to perform color measurements
using a digital camera?
RGB
RGB
RGB OUTPUT
CIE-XYZ
CIE-Lab
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Introduction
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colorimetric applications are seriously limited
Commercial digital color camera
CIE Color Matching Functions
Linear
Transformation
(Luther Condition)
Wavelength (nm)
400 450 500 550 600 650 700
xyz -
CIE
1931
0.0
0.5
1.0
1.5
2.0x - CIE 1931
y - CIE 1931
z - CIE 1931
Wavelength (nm)
400 450 500 550 600 650 700
xyz -
Q10 C
CD
co
lou
r cam
era
0.0
0.2
0.4
0.6
0.8
1.0x - Q10 CCD Colour Camera
y - Q10 CCD Colour Camera
z - Q10 CCD Colour Camera
Color Matching Functions of the
digital camera
Is it possible to perform color measurements
using a digital camera?
CIE-XYZ RGB
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Introduction
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The solution:
Multispectral Imaging
Systems
Is it possible to perform color measurements
using a digital camera?
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
What is a multispectral system?
An imaging system with more than 3 acquisition
channels
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A multispectral system is able to provide spectral information
instantaneously at each pixel of the captured image and therefore it
allows performing more accurate colour measurements.
Wavelength (nm)
400 450 500 550 600 650 700
Re
lati
ve
Sp
ectr
al
Se
ns
itiv
ity
Q1
0 C
CD
co
lou
r c
am
era
0.0
0.2
0.4
0.6
0.8
1.0
Wavelength (nm)
400 450 500 550 600 650 700 750
Tra
nsm
itta
nce
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
F400
F450
F500
F550
F600
F650
F700
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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CIE-1931 XYZ
Color Imaging
Multispectral Imaging
An imaging system with more than 3 acquisition
channels
What is a multispectral system?
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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An imaging system with more than 3 acquisition
channels
What is a multispectral system?
Complete spectral information on each pixel of the image
Color Image
R,G,B
Multispectral
Image
Wavelength (nm)
400 440 480 520 560 600 640 680 720 760
Spectr
al re
flecta
nce
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Classification:
They are classified depending on the number of spectral
bands/acquisition channels:
Number of channels Name
1 Monochromatic
3 RGB o trichromatic
4 to 9 Multispectral
10 to 100 Hyperspectral
More than 100 Ultraspectral
What is a multispectral system?
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Components of multispectral systems
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Potential of multispectral and hyperspectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Spectral sampling technique
1. Using a “white” light source and filters:
2. Multiplexed illumination:
+
Building acquisition channels with different
spectral features
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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1. Using a “white” light source and filters:
Narrowband filters: interference filters in a filter wheel
Configurations based on monochrome cameras
QImaging
QICAM Fast1394
12-bit cooled
Nikon AF
Nikkor
28-105mm
Motorized
Filter Wheel
QImaging
QICAM Fast1394
12-bit cooled
Nikon AF
Nikkor
28-105mm
Motorized
Filter Wheel
Wavelength (nm)
400 450 500 550 600 650 700 750
Tra
nsm
itta
nce
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
F400
F450
F500
F550
F600
F650
F700
Components of multispectral systems
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Spectral sampling techniques
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1. Using a “white” light source and filters:
Narrowband filters: tunable filter (LCTF or AOTF)
Configurations based on monochrome cameras
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Spectral sampling techniques
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2. Multiplexed illumination:
Configurations based on monochrome cameras
and light-emmiting diodes (LEDs)
http://www.cs.columbia.edu/CAVE/projects/multispectral_imaging/images/capturing_system.gif
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Calibrating a multispectral system
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High resolution
Linearity
Rapid response
Acceptable SNR
High cuantum efficiency
Wide spectral range
Reduced size
Scientific image
Measurement instrument
with high spatial resolution
2. Spectral reconstruction and color
measurement algorithm
Instrument for color and spectral measurements
1. Control and correction of the noise sources
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Calibrating a multispectral system
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1. Correction of the noise sources:
Temporal noise sources: Image averaging. Determining
the number of images to be averaged. Image averaging
removes all noise sources except the spatial noise sources.
# averaged images
0 10 20 30 40 50 60 70 80
Rela
tive S
NU
P
0.800
0.850
0.900
0.950
1.000
R Channel
G Channel
B Channel
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Calibrating a multispectral system
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1. Correction of the noise sources:
Spatial noise sources: Spatial non-uniformity correction,
flat-field correction or „flat-fielding‟.
560
580
600
620
640
660
01020304050607080
010
2030405060
Dig
ita
l V
alu
e
Colu
mns
Rows
560
580
600
620
640
660
560
580
600
620
640
660
01020304050607080
010
2030405060
Dig
ita
l Le
ve
l
Colu
mn
Row
560
580
600
620
640
660
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Calibrating a multispectral system
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2. Spectral reconstruction and color measurement
How can we obtain spectral properties (reflectance,
radiance…) from multispectral images?
Wavelength (nm)
400 500 600 700
Re
fle
cta
nce
0.2
0.4
0.6
0.8
1.0
1.2
ND r(l)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Use of training sets:
2. Spectral reconstruction and color measurement
Calibrating a multispectral system
ND r(l)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Multispectral systems at the CD6
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Multispectral system in the near-infrared (800 –
1000 nm)
800 1000 nm 380 780
VIS NIR
Expanding VIS techniques to NIR
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Multispectral systems at the CD6
Channel 1 Channel 2 Channel 3 Channel 4 Channel 5
1) Reflectance reconstruction system
Multispectral system in the near-infrared (800 –
1000 nm)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Multispectral systems at the CD6
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Multispectral system in the near-infrared (800 –
1000 nm)
Food
Wood Leather
Plastics
Fabrics
Marble
Plants
Paper, cardboard…
80 samples
(natural and manufactured)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Multispectral systems at the CD6
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Multispectral system in the near-infrared (800 –
1000 nm)
WIENER (Transformation 1)
Wavelength (nm)
750 800 850 900 950 1000 1050
Sp
ectr
al re
flecta
nce
0.0
0.2
0.4
0.6
0.8
1.0
Fabric (original)
Fabric (reconstructed)
WIENER (Transformation 1)
Wavelength (nm)
750 800 850 900 950 1000 1050
Sp
ectr
al re
flecta
nce
0.0
0.2
0.4
0.6
0.8
1.0
Red pepper (original)
Red pepper (reconstructed)
WIENER (Transformation 2)
Wavelength (nm)
750 800 850 900 950 1000 1050
Sp
ectr
al re
flecta
nce
0.0
0.2
0.4
0.6
0.8
1.0
Fabric (original)
Fabric (reconstructed)
WIENER (Transformation 2)
Wavelength (nm)
750 800 850 900 950 1000 1050
Sp
ectr
al re
flecta
nce
0.0
0.2
0.4
0.6
0.8
1.0
Red pepper (original)
Red pepper (reconstructed)
Prec > 99.9 % & RMSE < 1
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Wavelength (nm)
400 450 500 550 600 650 700
Rela
tive S
pec
tra
l S
en
sit
ivit
y
0.0
0.2
0.4
0.6
0.8
1.0
1.2 R Channel
G Channel
B Channel
QImaging
QICAM Fast1394
12 bit cooled
Nikon AF
Nikkor
28 – 105mm
RGB Tunable
Filter
QImaging
QICAM Fast1394
12 bit cooled
Nikon AF
Nikkor
28 – 105mm
RGB Tunable
Filter
7-channel camera
QImaging
QICAM Fast1394
12 bit cooled
Nikon AF
Nikkor
28 – 105mm
Motorized
Filter Wheel
QImaging
QICAM Fast1394
12 bit cooled
Nikon AF
Nikkor
28 – 105mm
Motorized
Filter Wheel
Wavelenght (nm)
400 450 500 550 600 650 700 750
Sp
ec
tra
l T
ran
sm
itta
nc
e
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
F400
F450
F500
F550
F600
F650
F700
RGB camera
Multispectral systems at the CD6
Multispectral system in the visible range (380 -
780 nm)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Multispectral systems at the CD6
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Multispectral system in the visible range (380 -
780 nm)
CCCR –
training & test
CCDC –
training & test
mean DE 3.91 3.02
min DE 0.46 0.47
max DE 14.91 9.70
Mathematical method: PSE
Number and features of the acquisition channels: 7 channels
Training and
Test
Color Rendition Chart (CCCR) DC Chart (CCDC)
Training and
Test
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Multispectral systems at the CD6
Multispectral system in the visible range (380 -
780 nm)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Pladellorens et al. Skin Res Appl 2008
Multispectral systems at the CD6
Multispectral system in the visible range (380 -
780 nm)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Wavelength (nm)
400 440 480 520 560 600 640 680 720 760
Sp
ectr
al re
fle
cta
nce
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
Vilaseca et al. Appl Opt 2008
Herrera et al. Col Res Appl 2011
Multispectral systems at the CD6
Multispectral system in the visible range (380 -
780 nm)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Multispectral system in the UV-VIS-IR range
composed of light-emitting diodes (LEDs)
Near UV-Vis-NIR (350-900nm) IR (900-1700nm)
Spectral
emission
900 1000 1100 1200 1300 1400 1500 1600 17000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavelength (nm)
Arb
itra
ry U
nits
Emission spectra for module 2
300 400 500 600 700 800 900 10000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavelength (nm)
Arb
itra
ry U
nits
Emission spectra for module 1
Multispectral systems at the CD6
Martínez et al. J Imaging Sci Technol (accepted 2011)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Near UV-Vis-NIR (350-900nm) IR (900-1700nm)
Imaging
Sensors
QICAM CCD HAMAMATSU InGaAs
Spectral
sensitivity
300 400 500 600 700 800 900 10000
0.2
0.4
0.6
0.8
1
Wavelength (nm)
Spectr
al S
ensitiv
ity
800 1000 1200 1400 1600 18000
0.2
0.4
0.6
0.8
1
Wavelength (nm)
Spectr
al S
ensitiv
ity
Multispectral system in the UV-VIS-IR range
composed of light-emitting diodes (LEDs)
Multispectral systems at the CD6
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Multispectral system in the UV-VIS-IR range
composed of light-emitting diodes (LEDs)
Multispectral systems at the CD6
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Multispectral system in the UV-VIS-IR range
composed of light-emitting diodes (LEDs)
Multispectral systems at the CD6
Senserrich & Font 2009
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Multispectral system in the UV-VIS-IR range
composed of light-emitting diodes (LEDs)
Multispectral systems at the CD6
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Applications in the automotive sector
Spectral and color information pixel by pixel
(Multispectral image)
Low cost: digital camera, filters, LEDs etc.
High speed: many spectra from one single measurement
(or few)
Benefits of multispectral systems:
XYZ CIE-Lab
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Potential applications:
Applications in the automotive sector
Conventional color (CIELAB) characterization of
materials used in the automotive sector: paints, plastics
etc. E.g.: Quality control.
But also SPECTRAL! (Avoiding metamerism, color fakes
etc.)
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Potential applications:
Applications in the automotive sector
Multi-angle spectral and color characterization of gonio-
chromatic materials: metallic and pearlescent colors,
interference pigments etc.
E.g.: Analysis of CIELAB at different angles (15° / 25° / 45° /
75° / 110° / -15º)
Analysis of texture (sparkle, graininess and mottling effects).
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Potential applications:
Applications in the automotive sector
Characterization of three-dimensional (3D) samples
E.g.: Planar and curved samples
To expand the spectral information beyond the visible
(VIS) range: UV (Ultraviolet) and IR (Infrared).
E.g.: Fluorescent pigments, detection of color replicates etc.
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Our current goal (UPC-UA):
Development of a gonio-multispectral system in
the UV-VIS-IR range (250-1700 nm) based on
light-emitting diodes (LEDs)
Applications in the automotive sector
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Our current goal (UPC-UA):
Development of a gonio-multispectral system in
the UV-VIS-IR range (250-1700 nm) based on
light-emitting diodes (LEDs)
Applications in the automotive sector
Automated system with diffuse & directional illumination
geometries:
- 6 aspecular viewing angles (15° / 25° / 45° / 75° / 110° / -15º)
- 3-angle circumferential illumination, 1-angle viewing geometry
http://www.byk.com http://www.konicaminolta.com
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Hyperspectral systems
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Imaging spectrograph + monochrome CCD camera
Camera with a diffractive element:
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
Hyperspectral systems
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Camera with a diffractive element:
Scene Spatial axis
λ
Image
Scanning of the scene
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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Spectral analysis of samples with complex spatial patterns:
Hyperspectral systems
Camera with a diffractive element:
Potential of multispectral techniques for measuring color in the automotive sector (1st BYK-Gardner Iberian Automotive Meeting, 2011)
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e-mail: [email protected]
CD6
GRACIAS !
Centre for Sensors, Instruments and Systems Development (CD6)
Dept. of Optics and Optometry
TECHNICAL UNIVERSITY OF CATALONIA (UPC)
TERRASSA