fourth oxford conference on spectrometry, davidson nc, june 9-13, 2002 analysis of spectrophotometer...
TRANSCRIPT
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Analysis of SpectrophotometerSpecular Performance Using
Goniophotometric Information
David R. WybleMunsell Color Science LaboratoryRochester Institute of Technology
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
• All integrating sphere spectrophotometers are not created equal
• Standards allow a wide range of conforming devices
• Sample gloss and specular port configuration can significantly affect measurements
Introduction
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
A Pathological Case
GM White ASPEX
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
400 450 500 550 600 650 700
Reflect
an
ce f
act
or
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
A more expected example…
Ford Tan ASPEX
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
400 450 500 550 600 650 700
Reflect
an
ce f
act
or
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
• Determine a relationship between the size of the specular port and the effective performance of the spectrophotometer in SPEX mode
• Create a method to correct measurements to allow comparison of results from instruments of differing configurations
Purpose
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
• CIE 15.2 Colorimetry• Theory on Effective Specular Port Size• Samples and Goniometric Measurements• Results & Conclusions
Outline
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
CIE 15.2 Colorimetry
1.4 Illuminating and viewing conditions for reflecting specimens
c) Diffuse/normal (symbol d/0):The specimen is illuminated diffusely by an integrating sphere. The angle between the normal to the specimen and the axis of the viewing beam should not exceed 10°. The integrating sphere may be of any diameter provided the total area of the ports does not exceed 10% of the internal reflecting sphere area. The angle between the axis and any ray of the viewing beam should not exceed 5°.
c) Diffuse/normal (symbol d/0):(Similar angular specifications)
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Reflectance: d/8 SPEX
Detector
Baffle
Incidentlight
8° viewing, diffuse illumination, SPIN
Sample
Specular cap“black cap”
excludes
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Reflectance: 8/d SPEX
Detector
Baffle
Incident light
Diffuse viewing, 8° illumination, SPEX
Sample
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
CIE 15.2 Colorimetry
1.4 Illuminating and viewing conditions for reflecting specimens
c) Diffuse/normal (symbol d/0):The specimen is illuminated diffusely by an integrating sphere. The angle between the normal to the specimen and the axis of the viewing beam should not exceed 10°. The integrating sphere may be of any diameter provided the total area of the ports does not exceed 10% of the internal reflecting sphere area. The angle between the axis and any ray of the viewing beam should not exceed 5°.
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
CIE 15.2 Colorimetry
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
CIE 15.2 Colorimetry
1.4 Illuminating and viewing conditions for reflecting specimens
c) Diffuse/normal (symbol d/0):The specimen is illuminated diffusely by an integrating sphere. The angle between the normal to the specimen and the axis of the viewing beam should not exceed 10°. The integrating sphere may be of any diameter provided the total area of the ports does not exceed 10% of the internal reflecting sphere area. The angle between the axis and any ray of the viewing beam should not exceed 5°.
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
CIE 15.2 Colorimetry
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
CIE 15.2 Colorimetry
1.4 Illuminating and viewing conditions for reflecting specimens
Note 1: For the conditions ‘diffuse/normal’ and ‘normal diffuse’ the regularly reflected component of specimens with mixed reflection may be excluded with a gloss trap. If a gloss trap is used, details of its size, shape, and position should be given,
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
CIE 15.2 Colorimetry
By inference, the angle from the normal to the gloss trap will not exceed 10°.
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
CIE 15.2 Colorimetry
No guidance on angular size of gloss trap.
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
CIE 15.2 Colorimetry
• All we are told about the specular port is to report the configuration used
• Still a range of configurations that meet the specification
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Specular Port Size
As port size grows …
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Specular Port Size
… more of the specular information …
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Specular Port Size
… is lost …
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Specular Port Size
… but how much?
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Where do we go now?
We need to know the details of how our instruments handle this
component of the reflected light.
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Where do we go now?
To do this, we first need to accurately characterize a set of samples, by measuring
their reflectance characteristics as a function of angle.
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
MCSL Goniometer
Light source
IR filterCollimator
Sample holder
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
MCSL GoniometerTechnical description
• Light source• 100 cm sphere• 2 interior 19.6V GE bulbs• Lamp current monitored and manually
maintained at 6.00A•IR filter •Collimation lens• Detector
• Photoresearch PR704 spectroradiometer• Aperture ~ 3°• Measurement units are integrated
radiance
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
MCSL GoniometerTechnical description
• Sample and detector angles independently adjustable within physical constraints
• Vernier scales allow repeatable angle settings to 0.5°
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
MCSL Goniometer
Sample
Physical constraints limit measurement angles to -8° to +75°,always referenced to the specular angle.
Incidentlight
0°Detector
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Theory
• Measure spectral reflectance using SPIN and SPEX modes
• Calculate the average difference between SPIN and SPEX data, in percent reflectance
• Determine the effective size of the specular port that would account for the above difference
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
SPIN and SPEX
GM Gray Smooth Matte
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
400 450 500 550 600 650 700
wavelength (nm)
Reflectance Factor
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Theory
• Measure spectral reflectance using SPIN and SPEX modes
• Calculate the average difference between SPIN and SPEX data, in percent reflectance
• Determine the effective size of the specular port that would account for the above difference
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
GM Gray Smooth Matte
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
400 450 500 550 600 650 700
wavelength (nm)
Reflectance Factor
Average Spectral Difference
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Theory
• Measure spectral reflectance using SPIN and SPEX modes
• Calculate the average difference between SPIN and SPEX data, in percent reflectance
• Determine the effective size of the specular port that would account for the above difference
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Effective Specular Port Calculation
• Measure radiance vs angle on goniometer
• Calculate cumulative volume as a function of radius
• Determine the radius that results in the percent cumulative volume that matches the SPIN-SPEX difference
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Radiance
Detection angle
Radia
nce
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Radiance vs 2D Detection Angle
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Effective Specular Port Diameter
• Measure radiance vs angle on goniometer
• Calculate cumulative volume as a function of radius. Normalize this volume to the average reflectance data for the sample.
• Determine the radius that results in the percent cumulative volume that matches the SPIN-SPEX difference
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Cumulative Volume vs Radius
degrees from specular angle
relative units
cumulative sumof volume
volume atthis radius
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Effective Specular Port Calculation
• Measure radiance vs angle on goniometer
• Calculate cumulative volume as a function of radius
• Determine the radius that results in the percent cumulative volume that matches the SPIN-SPEX difference
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Effective Specular Port Calculation
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
degrees from specular angle
relative units
Effective Specular Port Calculation
currentradius
volume insidethat radius
reff
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Effective Specular Port Calculation
effective radius equation:
Search through radii until we match the average SPIN-SPEX spectral difference
€
SPEX =sampletotal − sampleradprd total − prdrad
€
SPIN =sampletotalprd total
€
ΔR =1−SPEX
SPIN
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Searching…
Detection angle
rad
ian
ce
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Searching…ra
dia
nce
Detection angle
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Searching…ra
dia
nce
Detection angle
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Searching…ra
dia
nce
Detection angle
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Searching…ra
dia
nce
Detection angle
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Found
“SPIN”-“SPEX”
SPIN = total
rad
ian
ce
Detection angle
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental:Spectrophotometers
• Four commercial-grade benchtop devices:– Datacolor Spectraflash 600+– Macbeth Coloreye 7000– BYK-Gardner The Color Sphere– Minolta 3600-d
• All are d/0 devices• All have reasonable calibration status
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental:Spectrophotometers
• Specifically chosen for their range of specular port configurations, from <1” to 2”
• One (Minolta) has a detector in place of the specular port. SPIN and SPEX are calculated using the signal gathered by that detector
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental:Samples
• Two different automotive plastic samples (gray, tan)
• Three levels of gloss• Total of five samples, two highly glossy,
and three at two levels of matte surface• Underlying color identical, since various
gloss levels are stamped in the same piece of plastic
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental:Samples
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental:Sample Set
Color Description
gray
GlossySmooth MatteRough Matte
tanGlossy
Smooth Matte
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental:Samples
Smooth matteRough matte
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
For Reference:Measured Gloss
Color Level 20° 60° 85°
gray
glossysmooth matterough matte
49.20.70.5
65.64.73.5
94.322.36.5
tanglossy
smooth matte56.20.6
69.74.5
94.120.1
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Goniometric Results:measured radiance
Note alternate ordinate axis for glossy samples.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90
angle from specular (°)
measured radiance
0
5
10
15
20
25
30
measured radiance
Gray Smooth Matte
Gray Rough Matte
Tan Smooth Matte
Gray Glossy
Tan Glossy
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental Results:Cumulative volume
0
0.05
0.1
0.15
0.2
0.25
0.3
0 10 20 30 40 50 60 70 80 90
angle from specular (°)
normalized cumulative volume
Gray Glossy
Gray Smooth Matte
Gray Rough Matte
Tan Glossy
Tan Smooth Matte
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental Results:Cumulative volume
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
0 1 2 3 4 5 6 7 8 9 10angle from specular (°)
normalized cumulative volume
Gray Glossy
Gray Smooth Matte
Gray Rough Matte
Tan Glossy
Tan Smooth Matte
PRD
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental Results:Effective Specular Port Size (°)
*** Minolta 3600-d has specular sensor
DatacolorSF600
Macbeth CE7000
BYK-Gardner
TCS
Minolta 3600-d
Gray Glossy 1.9 1.9 2.0 2.0
Gray Smooth Matte 7.6 4.2 3.2 5.1
Gray Rough Matte 8.3 5.0 3.9 4.7
Tan Glossy 3.7 3.2 3.3 3.3
Tan Smooth Matte 6.2 4.8 5.8 7.5
“Actual” 4.7 3.0 3.6 ***
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
0
1
2
3
4
5
6
7
8
9
3.5 4 4.5 5 5.5
measured port width (°)
effective port width (°)
Gray Glossy
Gray Smooth Matte
Gray Rough Matte
Tan Glossy
Tan Smooth Matte
matte samples
glossy samples
Experimental Results:Effective Specular Port Size (°)
CE7000TCS
SF6000+
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Experimental Results:Effective Specular Port Size (°)
0
1
2
3
4
5
6
7
8
9
3.5 4 4.5 5 5.5
measured port width (°)
effective port width (°)
Gray Glossy
Gray Smooth Matte
Gray Rough Matte
Tan Glossy
Tan Smooth Matte
matte samples
glossy samples
Minolta data
at arbitrary
port width
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Assumptions and Limitationsor “Opportunities”
• Specular port vs sphere wall• Specular port uniformity• More comprehensive sample set• Viewing/illumination beam• Relationship to Gonio collimation
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Conclusions
• Overall trend among spectrophotometers agrees with the physical measure
• Ability to compare traditional designs to those with electronic port detection
• May aid in device selection to best accommodate the application
• Goal of inter-instrument correction not realized
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
Acknowledgements
This work was supported by theMunsell Color Science Laboratory
Special thanks are due to:– Danny Rich– Mark Fairchild– Roy Berns– Mitch Rosen
who all helped tremendously with many fruitful discussions and emails.
Fourth O
xford Conference on S
pectrometry, D
avidson NC
, June 9-13, 2002
That’s all.Thanks for listening!