Transcript First thoughts - RIT Center for Imaging Science

David R. Wyble
Munsell Color Science Laboratory
Rochester Institute of Technology
[email protected]
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Analysis of Spectrophotometer
Specular Performance Using
Goniophotometric Information
Introduction
Fourth Oxford Conference on Spectrometry, Davidson 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
A Pathological Case
0.70
GM White A
SPEX
Reflectance factor
0.60
0.50
0.40
0.30
0.20
0.10
0.00
400
450
500
550
600
650
700
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
0.80
A more expected example…
0.40
Ford Tan A
SPEX
Reflectance factor
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
400
450
500
550
600
650
700
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
0.45
Purpose
Fourth Oxford Conference on Spectrometry, Davidson 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
Outline
CIE 15.2 Colorimetry
Theory on Effective Specular Port Size
Samples and Goniometric Measurements
Results & Conclusions
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
•
•
•
•
CIE 15.2 Colorimetry
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 Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
1.4 Illuminating and viewing conditions for reflecting
specimens
Reflectance: d/8 SPEX
Detector
Incident
light
Baffle
Sample
8° viewing, diffuse illumination, SPIN
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Specular cap
“black cap”
excludes
Reflectance: 8/d SPEX
Detector
Baffle
Sample
Diffuse viewing, 8° illumination, SPEX
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Incident light
CIE 15.2 Colorimetry
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 Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
1.4 Illuminating and viewing conditions for
reflecting specimens
CIE 15.2 Colorimetry
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
CIE 15.2 Colorimetry
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 Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
1.4 Illuminating and viewing conditions for
reflecting specimens
CIE 15.2 Colorimetry
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
CIE 15.2 Colorimetry
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 Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
1.4 Illuminating and viewing conditions for
reflecting specimens
CIE 15.2 Colorimetry
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
By inference, the angle from the normal to the gloss trap
will not exceed 10°.
CIE 15.2 Colorimetry
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
No guidance on angular size of gloss trap.
CIE 15.2 Colorimetry
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• All we are told about the specular port is to
report the configuration used
• Still a range of configurations that meet the
specification
Specular Port Size
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
As port size grows …
Specular Port Size
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
… more of the specular information …
Specular Port Size
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
… is lost …
Specular Port Size
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
… but how much?
Where do we go now?
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
We need to know the details of how our
instruments handle this component of the
reflected light.
Where do we go now?
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
To do this, we first need to accurately characterize a set
of samples, by measuring their reflectance
characteristics as a function of angle.
MCSL Goniometer
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Sample holder
Collimator
IR filter
Light source
MCSL Goniometer
Technical description
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
MCSL Goniometer
Technical description
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• Sample and detector angles independently
adjustable within physical constraints
• Vernier scales allow repeatable angle settings to
0.5°
MCSL Goniometer
Sample
+q
0°
-q
Incident
light
Physical constraints limit measurement angles to -8° to +75°,
always referenced to the specular angle.
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Detector
Theory
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
SPIN and SPEX
0.30
GM Gray
Smooth Matte
Reflectance Factor
0.25
0.20
0.15
0.10
0.05
0.00
400
450
500
550
wavelength (nm)
600
650
700
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
0.35
Theory
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
Average Spectral Difference
0.30
GM Gray
Smooth Matte
Reflectance Factor
0.25
0.20
0.15
0.10
0.05
0.00
400
450
500
550
wavelength (nm)
600
650
700
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
0.35
Theory
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
Effective Specular Port Calculation
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
Detection angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Radiance
Radiance
Radiance vs
2D Detection Angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Effective Specular Port Diameter
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
Cumulative Volume vs Radius
relative units
cumulative sum
of volume
degrees from specular angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
volume at
this radius
Effective Specular Port Calculation
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
Effective Specular Port Calculation
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
reff
volume inside
that radius
current
radius
degrees from specular angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
relative units
Effective Specular Port Calculation
Effective Specular Port Calculation
sam pletotal - sam plerad
SPEX 
prdtotal - prdrad


sam pletotal
SPIN 
prdtotal
SPEX
R 1SPIN
Search through radii until we match the
average SPIN-SPEX
spectral difference

Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
effective radius equation:
Detection angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
radiance
Searching…
Detection angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
radiance
Searching…
Detection angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
radiance
Searching…
Detection angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
radiance
Searching…
Detection angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
radiance
Searching…
“SPIN”-“SPEX”
SPIN = total
Detection angle
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
radiance
Found
Experimental:
Spectrophotometers
–
–
–
–
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 Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• Four commercial-grade benchtop devices:
Experimental:
Spectrophotometers
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
Experimental:
Samples
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
Experimental:
Samples
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Experimental:
Sample Set
gray
tan
Description
Glossy
Smooth Matte
Rough Matte
Glossy
Smooth Matte
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Color
Experimental:
Samples
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Smooth matte
Rough matte
For Reference:
Measured Gloss
Level
20°
60°
85°
gray
glossy
smooth matte
rough matte
49.2
0.7
0.5
65.6
4.7
3.5
94.3
22.3
6.5
tan
glossy
smooth matte
56.2
0.6
69.7
4.5
94.1
20.1
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Color
Goniometric Results:
measured radiance
30
Gray Smoot h Mat t e
Gray Rough Mat t e
0.9
T an Smooth Mat t e
Note alternate
ordinate axis for
glossy samples.
25
Gray Glossy
0.8
T an Glossy
20
0.6
0.5
15
0.4
10
0.3
0.2
5
0.1
0
0
-90
-75
-60
-45
-30
-15
0
15
angle from specular (°)
30
45
60
75
90
measured radiance
measured radiance
0.7
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
1
Experimental Results:
Cumulative volume
Gray Glossy
Gray Smooth Matte
Gray Rough Matte
0.25
T an Glossy
normalized cumulative volume
T an Smooth Matte
0.2
0.15
0.1
0.05
0
0
10
20
30
40
50
60
angle from specular (°)
70
80
90
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
0.3
Experimental Results:
Cumulative volume
Gray Glossy
Gray Smooth Matte
0.018
Gray Rough Matte
T an Glossy
0.016
normalized cumulative volume
T an Smooth Matte
P RD
0.014
0.012
0.01
0.008
0.006
0.004
0.002
0
0
1
2
3
4
5
6
7
angle from specular (°)
8
9
10
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
0.02
Experimental Results:
Effective Specular Port Size (°)
Macbeth
CE7000
BYKGardner
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
***
*** Minolta 3600-d has specular sensor
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
Datacolor
SF600
Experimental Results:
Effective Specular Port Size (°)
matte samples
Gray Glossy
8
Gray Smooth Matte
Gray Rough Matte
7
effective port width (°)
T an Glossy
6
T an Smooth Matte
5
4
3
glossy samples
2
1
TC
S
CE7000
SF6000+
0
3.5
4
4.5
measured port width (°)
5
5.5
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
9
Experimental Results:
Effective Specular Port Size (°)
matte samples
Gray Glossy
8
Gray Smooth Matte
Minolta data
at arbitrary
port width
Gray Rough Matte
7
effective port width (°)
T an Glossy
6
T an Smooth Matte
5
4
3
2
1
glossy samples
0
3.5
4
4.5
measured port width (°)
5
5.5
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
9
Assumptions and Limitations
or “Opportunities”
Specular port vs sphere wall
Specular port uniformity
More comprehensive sample set
Viewing/illumination beam
Relationship to Gonio collimation
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
•
•
•
•
•
Conclusions
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
• 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
Acknowledgements
Special thanks are due to:
– Danny Rich
– Mark Fairchild
– Roy Berns
– Mitch Rosen
who all helped tremendously with many fruitful
discussions and emails.
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
This work was supported by the
Munsell Color Science Laboratory
Fourth Oxford Conference on Spectrometry, Davidson NC, June 9-13, 2002
That’s all.
Thanks for listening!