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Comparison of Color Difference Methods for multi-angle Application
Konrad Lex, BYK-Gardner GmbH
10th BYK-Gardner User Meeting, Innsbruck Austria – April 2013
Page 2, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Effect Coatings 70% of todays automotive finishes are effect coatings
• Pearlescent coatings result in a more spectacular color effect: Color Flop
• Metallic coatings accentuate the curved profile: Light – Dark Flop
• Effect finishes with special glitter effect (XirallicsTM)
Page 3, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
L* = 100
+a*
-a*
+b*
-b* Blue
Red
Green
Yellow L* = + 58,12
a* = + 30,41
b* = + 36,26
L* = 0
CIELab - System: L*a*b*- Coordinates
Page 4, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
E* = √ (L*)2 + (a*)2 + (b*)2
= Sample - Standard
- +
- +
- +
L*
a*
b* Sample
E* L*
b*
a* Standard
CIELab - System: Color Difference L*, a*, b*
Page 5, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
L* = 100
+a*
-a*
+b*
-b*
270°
0°
180°
90°
L* = + 58,12
C* = + 47,32
h° = 50°
L* = 0
h°
C*
CIELab - System: L*C*h°- Coordinates
Page 6, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
+a*
Sample
Standard
C*ab
h°ab h°ab
C*ab
+H*
+b*
CIELab - System: Color Differences C* und H*
E* = √ (L*)2 + (C*)2 + (H*)2
-C*
Page 7, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
CIELab - System: Chromatic – Non Chromatic
+ b*
- b*
+ a* - a* B
P
C*
H*
Non-chromatic colors: C* < 10
Use L*a*b*
Chromatic colors: C* > 10
Use L*C*h°
Page 8, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
CIELab - System: Typical Tolerances
0.5 0.5 1.0 45°
b* a* L*
Metallics
0.5 0.5 1.0 45°
Solids
0.5 0.5 1.0 110°
0.5 0.5 1.0 75°
0.7 0.7 1.5 25°
1.0 1.0 2.0 15°
-15° 1.0 1.0 2.0
*Measurement of Metallic & Pearlescent Colors
Allan Rodrigues, DuPont, 1990
Achromatic
Page 9, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
CIELab - System: Typical Tolerances
110° 1.0
1.0 75°
1.0 2.0 1.5
45°
25°
15°
-15°
H* C* L*
1.0 2.0
1.0 2.0
1.2 2.2
1.5 2.5
1.5 2.5
2.0
3.0
3.0
Chromatic
Metallics
1.0 2.0 1.5 45°
Solids
Page 10, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Color Difference
Delta CIE Lab:
What causes the problem?
Compare to tolerances:
dH* is too large!
Page 11, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Weighted Color Difference CMC – Color Difference Formula
Delta E cmc:
Page 12, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Weighted Color Difference CMC – Color Difference Formula
H S
c cS
lS L
• 3-dimensional ellipsoid with axes corresponding to
hue, chroma and lightness
• Weighting functions (= semi-axis) SL, SC and SH
are dependent on color of standard
• Factors l and c modify the lengths of relevant
semi-axes
( )
2 1 2
ab
2
ab
2
: CMC
* H * C * L E
+
+
=
H C L
c l S cS lS
Page 13, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Weighted Color Difference General Color Difference Formula
measurement geometry
application parameter e.g. batch or production
weighting factor
tolerance
222
)(
)(*
)(
)(*
)(
)(*)(
+
+
=
bbaaLL
wSg
b
Sg
a
Sg
LE
Achromatic:
Chromatic:
222
)(
)(*
)(
)(*
)(
)(*)(
+
+
=
HHCCLL
wSg
H
Sg
C
Sg
LE
g
SSg
Page 14, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Weighted Color Components
Achromatic:
Chromatic:
)(
)(*)(
L
wTol
LL
=
)(
)(*)(
a
wTol
aa
=
)(
)(*)(
b
wTol
bb
=
)(
)(*)(
L
wTol
LL
=
)(
)(*)(
C
wTol
CC
=
)(
)(*)(
H
wTol
HH
=
Lw, a
w, bw, C
w, Hw
< 1.00 within Tolerance
Lw, a
w, bw, C
w, Hw
> 1.00 out of Tolerance
Page 15, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Weighted Color Difference CMC – Color Difference Formula
Delta E cmc:
Weighted by dE cmc Tolerances
dH* is 31% too large!
Page 16, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
How to get Tolerances? Weighted Color Difference Methods
E‘DIN
E‘BMW
Calculation of the
weighting factors are
measurement
geometry dependent
Weighting factors
independent from
measurement
geometry
ECMC
E00 E‘AUDI2000
Weighting factors
are dependent on
lightness flop and
color flop
E94 With Lightness
Correction
There is only one standard, DIN 6175-Part 2 for gonio appearant colors
Page 17 BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Silver Metallic Achromatic light metallic
Page 18 BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Red Metallic Chromatic medium light metallic
Page 19, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Yellow Metallic Chromatic light metallic
Page 20, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Solid White Achromatic light solid
Page 21, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
How to get Tolerances? Weighted Color Difference Methods
E‘DIN
E‘BMW
Optimized for light
metallic finishes
Discontinuity
between solid and
gonioapparent colors
Optimized for solid,
high chromatic colors
ECMC
E00 E‘AUDI2000
Applicable for
metallic and solid
E94 With Lightness
Correction
Page 22, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Weighted Deltas
Unweighted Deltas
Weighted Deltas
Unweighted Deltas
Weighted Deltas
Page 23, BYK-Gardner GmbH, Comparison of Color Difference Methods for multi-angle Application
Conclusion
• All color difference methods with weighting factors are closer to the visual than dE* method because L, a, b, C and H have different visual sensitivities depending on color.
• Gonioappearant colors may end up with 5 to 25 different tolerances weighted color components make the life much easier because the tolerances of weighted color components are always 1.00
Thank you for your Attention!
