Post on 06-Mar-2018
Color Management at AUDI
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General Information on AUDI
Color Management at AUDI, DCC, Detroit March 2012
► Audi is a daughter of Volkswagen
► Audi is Germany‟s 2nd biggest manufacturer of premium cars.
► 1.3 million cars in 2011
► 65000 employees
► 5 production sites
Ingolstadt, Germany
Neckarsum, Germany
Brussels, Belgium
Gyoer, Hungaria
*Sant‟Agata, Italy
**Bratislava, Slovakia
***Matorell, Spain
*** Changchun, China
* Lamborghini ** Cooperation with Volkswagen *** Cooperation with SEAT **** Cooperation with FAW
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Expectation of a Customer
The car should look as if all parts were painted together. The color travel should be harmonic.
Color Management at AUDI, DCC, Detroit March 2012
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Challenge
► Fulfill the expectation of you customer!
► The challenge is heavily
underestimated.
► Checking the quality at the end of the
assembly is not really helpful,
because you supply chain is full.
► Set up a process that takes effect
earlier.
► Have everybody check his painted parts
before shipment.
Color Management at AUDI, DCC, Detroit March 2012
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Production Reality
►Numerous add-on-parts
►Different substrates
►Different suppliers
►Different basecoat materials
►Different clearcoat materials
►Different layers
►Different applications
►Bumpers
►All sorts of covers
►Door handles
►Mirror housings
►Spoilers
►Moldings
►Fuel flaps
►Fenders
►Tailgates Color Management at AUDI, DCC, Detroit March 2012
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Reality – Reaction delay
Production
Storage
14-18 days
14-18 days
Paintshop 1 day
Stock Add-on-parts 1-90 days
S 1-4 month
Reac
tio
n t
ime
co
lor
Assembly 1 day
Color Management at AUDI, DCC, Detroit March 2012
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Integration AUDI A4 - Rear Bumper
Color Management at AUDI, DCC, Detroit March 2012
1972 1978 1986
1991
1994 2000 2004
2008
Quelle: Wikipedia
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Integration AUDI A6 - Front Bumper
Color Management at AUDI, DCC, Detroit March 2012
Audi 100 C1
1968 - 1976
Audi 100 C2
1976 - 1982
Audi 100 C3
1982 - 1990
Audi A6 C4
1994 - 1997
Audi A6 C5
1997 - 2004
Audi A6 C6
2005 - 2011
Audi A6 C7
2011-
Source: Wikipedia, Audi
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Example BMW
Color Management at AUDI, DCC, Detroit March 2012
E21
E30
E36
E46
E90
Source: Wikipedia
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Problems with Visual Assessment
► Homogeneity of references.
► Environmental influences (illumination, geometrical effects …).
► Individual tolerance limits.
► Different assessment situations:
► Car – harmony matching
► Single part – reference matching
You have to be a fortune teller whether there will be color
harmony.
► The more parts meet in one area the more critically assessed will
be color differences.
► Insufficient color memory.
► Tolerance drifting.
Color Management at AUDI, DCC, Detroit March 2012
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AUDI - Solution
► Use colorimetriy to describe color.
► Use one reference instead of multiple references.
measurement of the master standard – digitally distributed.
► Use tolerances to tell you suppliers what you await and accept.
► Use quality numbers and classification system to signal.
Necessary because ~70% are effect colors.
► In 1995 AUDI specified color measurement and tolerances for the
batch approval.
► In 1996 AUDI started with color management to handle the
complexity of colored add-on-parts and bodies.
Color Management at AUDI, DCC, Detroit March 2012
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AUDI nomenclature – CIE-nomenclature
CIE AUDI
Weighting function sdL,sdC,sdH gdL,gdC,gdH,gda,gdb,
Parametric factors k s
Aspecular angles
incident angle 45°
f gi
i = 1…n
g=15°…110°
Color Management at AUDI, DCC, Detroit March 2012
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Color Difference Calculation
Color Management at AUDI, DCC, Detroit March 2012
)max(
1
10*
max
110
15
2
,
2
,
2
,
2
,
2
,
2
,
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
dEdE
dEn
mdE
gs
dH
gs
dC
gs
dLdE
L*C*C
gs
db
gs
da
gs
dLdE
n
i
i
dHdHdCdCdLdL
dbdbdadadLdL
:cases other all
27 18 or
g = weighting function color and angle dependant. S = scaling factors to extend the model for different purpose g = aspecular angle – incident angle 45° L*, C*, dL, db, da, dC, dH in CIELab
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Scaling (parametric) factors to apply the model for different purpose
Color Management at AUDI, DCC, Detroit March 2012
2.18.10.2
2.12.10.2
0.1
dHdCdL
dbdadL
dHdCdbdadL
sss
sss
sssss
; ;
:case chromatic
; ;
:case achromatic
:parts-on-hang and body
:approval batch
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Classification Rules
Color Management at AUDI, DCC, Detroit March 2012
rejection -ok not 73.1
harmonycheck -ok cond73.141.1
on go -ok 41.10
:parts-on-hang andbody
rejection automatic -ok not 73.1
productioncheck -ok cond 73.141.1
acceptedlly automaticabatch -ok 41.10
:approvalbatch
max
max
max
mdE
mdE
mdE
dE
dE
dE
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Benefit of the AUDI Solution
► Your supplier knows exactly what you want.
► Colorimetriy provides you with a perfect memory – you will be able
to trace cause and effect .
► Higher stability with batches
► Better color harmony on cars
Color Management at AUDI, DCC, Detroit March 2012
Batch Approval:
Red: visual
Green: metrological
before
after
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Effect on Batch to Batch Variation
Color Management at AUDI, DCC, Detroit March 2012
Red: visual
Green: metrological
before
after
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Effect on Production
Color Management at AUDI, DCC, Detroit March 2012
before after
bumper
bodies
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Implementation of Color Management
► AUDI measures aprox. 3%-5% of its produced bodies.
► 15 persons for color measurement .
► 25 spectrophotometers in use.
► Suppliers have to measure in a similar frequency.
At least 1 carrier of every paint batch.
► Quality department does report weekly on color.
Color Management at AUDI, DCC, Detroit March 2012
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Examples – Optimizing Color by Application and Tinting
Color Management at AUDI, DCC, Detroit March 2012
Application
optimizing
Tinting effect
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Example – Clearcoat Exchange
Color Management at AUDI, DCC, Detroit March 2012
Clearcoat
Exchange
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Example – Monitoring Bodies and Hang-on-Parts
Color Management at AUDI, DCC, Detroit March 2012
orange: Hang-on-Part meas. by Audi
blue: Hang-on-Part meas. by Supplier
red: Production Audi
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Future Trend of Color Management
► Integration of particle measurement
sparkling and coarseness (= graininess).
► AUDI already specified tolerances for sparkle and coarseness based
on a visual assessment .
► The additional measurement is already fixed in an AUDI
specification and will be taken over into Volkswagen.
► No formula to combine color, particle and texture.
Color Management at AUDI, DCC, Detroit March 2012
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Sparkle
Color Management at AUDI, DCC, Detroit March 2012
Sparkle = light reflections to be seen under spot-like illumination e.g. sunlight. To be measured only by BYK-Mac. Measurement angles 15°,45° and 75°.
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Coarseness/Graininess
Color Management at AUDI, DCC, Detroit March 2012
Coarseness = texture to be seen under diffuse illumination e.g. cloudy day or light booth. To be measured only by BYK-Mac.
AUDI Tolerance Models
Color Management at AUDI, DCC, Detroit March 2012
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AUDI nomenclature – CIE-nomenclature
CIE AUDI
Weighting function sdL,sdC,sdH gdL,gdC,gdH,gda,gdb,
Parametric factors k s
Aspecular angles
incident angle 45°
f gi
i = 1…n
g=15°…110°
Color Management at AUDI, DCC, Detroit March 2012
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Tolerance Model AUDI95 - Effect Colors
► The tolerance model AUDI95 was developed for the batch approval
of effect paints.
► The model is based on batch panels of 36 effect colors from mainly
one observer over a long period of time.
► For each color between 20 to 100 batch panels from different
suppliers were used.
► In 1996 the model was modified to be used for bodies and hang-on-
parts.
► This model became DIN 6175-2
Other than AUDI, where tolerances are exactly specified for every
color, the DIN model had to deal with the two variants – dLCH and
dLab tolerancing. Therefore an exponential -function was
implemented to smooth the cliff between chromatic and
achromatic cases.
Color Management at AUDI, DCC, Detroit March 2012
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Tolerance Model AUDI95 – Solid Colors
► For solid paints we had not enough colors to find a mathematical
description. So we fixed tolerances for the few solids.
► For new colors we used the similarity principle:
► similar Chroma -> similar gdC and -> similar gdH
► similar Lightness -> similar gdL
► Achromatic colors
gdL, gda, gdb = 0.3
Color Management at AUDI, DCC, Detroit March 2012
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Look Up Table Tolerances for Solids AUDI95
Color Management at AUDI, DCC, Detroit March 2012
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Color Difference Calculation
Color Management at AUDI, DCC, Detroit March 2012
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Weighting Functions AUDI95
Color Management at AUDI, DCC, Detroit March 2012
Important Note: These weighting functions are calculated for the AUDI tolerance limit = 1.41. To apply them to a dE-limit of 1.00 multiply the weightings by 1.41² = 2.0.
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dE Calculation Extended
Color Management at AUDI, DCC, Detroit March 2012
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Development of AUDI2000
► Around 2000 we got more and more effect colors with very small
mica pigments.
These colors showed almost no gonio dependency of the viewing
angle – they were almost not to discriminate from the color of a
equivalent solid color.
The AUDI Tolerance Model AUDI95 failed for these colors.
We had to combine tolerances for solids with tolerances for effect
paints.
Color Management at AUDI, DCC, Detroit March 2012
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Development of AUDI2000
The main questions for me were:
► What is the difference between silver and grey or white?
► Why does one recognize a silver car in a photo?
Color Management at AUDI, DCC, Detroit March 2012
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Theoretical Modelling
Color Management at AUDI, DCC, Detroit March 2012
► The main difference between solid and effect colors is the flop.
Probably due to the angular vision lightness discrimination is
correlated with the lightness grade of focus.
► This answer satisfies both questions.
Experiments with masks showed that the smaller the area to be
seen, the less was the perceived metallic effect.
EffectSolid ggconstg
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General Form
► Based on the mental experiment, the AUDI95 data, and some
examples of “solid-like” effect colors.
► Best performance was to be found with solid-color term based on
C*45 even for the lightness weighting factor and not on L*45.
► The difference between effect und solid for achromatic colors in
gda* and gdb* could not be solved.
► The solid weighting gda* = gdb* = 0.3 was implemented instead of 0.5
from AUDI95.
Color Management at AUDI, DCC, Detroit March 2012
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Weighting functions AUDI2000
Color Management at AUDI, DCC, Detroit March 2012
Important Note: These weighting functions are calculated for the AUDI tolerance limit = 1.41. To apply them to a dE-limit of 1.00 multiply the weightings by 1.41² = 2.0.
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Weighting functions AUDI2000
Color Management at AUDI, DCC, Detroit March 2012
110° measurement angle:
-15° measurement angle:
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Modeling Weighting Functions AUDI2000 for Cg* <= 10
Color Management at AUDI, DCC, Detroit March 2012
The weighting functions of AUDI2000 are build in such way, that for Cg
* <= 10 the weights for dL, dC and dH will become aprox. equal, thus the tolerance space is spherical. In some cases gdH becomes larger than sdC. In that case the average will be used for both.
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AUDI2000 weighting functions – Flop and Chroma
Color Management at AUDI, DCC, Detroit March 2012
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
0
1
2
3
4
5
6
flop/deg
g A
U D
I 2 0 0 0
gdL - C* = 5
gdC - C* = 5 gdH - C* = 5
gdL - C* = 20
gdC - C* = 20 gdH - C* = 20
gdL - C* = 50
gdC - C* = 50 gdH - C* = 50
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AUDI2000
► In a conversation Melgosa and Huertas (Univ. Granada) pointed out that AUDI2000 is
very similar to CIE94 if the flop terms are omitted.
► So AUDI2000 should correct the major non- uniformities of CIE76 as good as CIE94.
► gdL
► Weak chroma dependence 0.002C* almost has no influence thus
gdl AUDI 2000 ~ const. as is gdl CIE94
► Ratio of the coefficients in gdC and gdH are very similar:
► AUDI2000 = 0.014/0.004 = 3.5
► CIE94 = 0.045 / 0.015 = 3.0
► Difference between AUDI2000 and CIE94 is, that AUDI2000 is only 2/3 of CIE94.
► Major difference to all modern color difference formulas is the flop dependence. For
solids this term is close to zero. The bigger flop the bigger will be the weights gdL ,
gdC, gdH .
Color Management at AUDI, DCC, Detroit March 2012
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AUDI2000 vs CIE94 – without flop term
Color Management at AUDI, DCC, Detroit March 2012
0 20 40 60 80 100
0.0
0.5
1.0
1.5
2.0
2.5
3.0
C*
g d L
AUDI2000 CIE94
0 20 40 60 80 100
0
1
2
3
4
5
6
C*
g d C
AUDI2000 CIE94
0 20 40 60 80 100
0.0
0.5
1.0
1.5
2.0
2.5
3.0
C* g d H
AUDI2000 CIE94
Comparism AUDI2000 and CIE94
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Flop Dependence of gdL for real Metallic, Mica and Solid Shades
Color Management at AUDI, DCC, Detroit March 2012
Highest flop values ~ 3.5/deg
20 40 60 80 100
0
1
2
3
4
5
aspecular angle[deg]
g d L
C* = 5.0 silver/gray
solid like effect
perl white
solid white
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Comparism gdL AUDI2000 with Dupont
Color Management at AUDI, DCC, Detroit March 2012
Highest flop values ~ 3.5/deg
20 40 60 80 100
0
1
2
3
4
5
aspecular angle[deg]
g d L
C* = 5.0 silver/gray
solid like effect
perl white
solid white
Audi2000
Dupont
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Flop Dependence of gdC for real Metallic, Mica and Solid Shades
Color Management at AUDI, DCC, Detroit March 2012
Highest flop values ~ 1.4/deg
20 40 60 80 100
0
2
4
6
aspecular angle[deg]
g d C
normal
solid-like
solid
reverse
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Flop Dependence of gdH for real Metallic, Mica and Solid Shades
Color Management at AUDI, DCC, Detroit March 2012
20 40 60 80 100
0.0
0.5
1.0
1.5
2
.0
2.5
3.0
3.5
aspecular angle[deg]
g d H
normal
solid-like
solid
reverse
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Weighted Color Differences
Color Management at AUDI, DCC, Detroit March 2012
To ease the communication with our suppliers, we use weighted color differences to specify the details. To make it more obvious what type of difference coordinates we use, we use the apostrophe „ instead of an asterisk * as is used for CIELab coordinates.
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Pass/Fail decision for Effect Colors
Color Management at AUDI, DCC, Detroit March 2012
In the case of effect colors pass/fail decision is not as strait forward as is for solids. AUDI is using 2 different numbers dEmax for batch approval mdE for bodies and hang-on-parts
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Classification Rules
Color Management at AUDI, DCC, Detroit March 2012
for batch approval bodies and hang-on-parts
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New Tolerance Model
Color Management at AUDI, DCC, Detroit March 2012
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Knowledge
► There is no gap between effect colors and solid colors.
► The stronger the flop in lightness, chroma and/or hue is the more
tolerant is the customer to color differences.
► Human color perception is based rather on contrast vision than on
the absolute color.
► Differences in sparkle and especially coarseness affect the
acceptance of color differences.
Latest experiences showed a bigger influence of coarseness whereas
sparkle seems less important.
► Crispening effect is probably the reason why for inlay parts the
tolerances are very small.
► AUDI2000 performs pretty good. Since 10 years approved.
Color Management at AUDI, DCC, Detroit March 2012
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Requirement Profile of New Color Tolerance Formula
► One formula for all kinds of colors – solid colors as well as effect
color.
► dH – modeling should be based on hue-flop otherwise the tolerance
for hue-differences will be heavily underestimated in case of hue
shifting pigments.
► The visibility of particles and coarseness and their interaction on
tolerance has to be taken into account.
► The work of Melgosa/Huertas showed an interaction between the
color tolerance and the coarseness, so at least coarseness has to be
included into the weighting functions.
► Gap effect should be taken into the formula.
Crispening effect ~ batch tolerance.
► Optional:
Surface effects caused by matted clearcoats.
Surface effects by textile or structured plastics. Color Management at AUDI, DCC, Detroit March 2012
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Thank you.