Colorimetric at AUDI - detroitcc.org Management at AUDI (DCC March 2012).pdf · 2 General Information on AUDI Color Management at AUDI, DCC, Detroit March 2012 Audi is a daughter

Color Management at AUDI

2

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

3

Expectation of a Customer

The car should look as if all parts were painted together. The color travel should be harmonic.


4

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.


5

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

6

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


8

Integration AUDI A4 - Rear Bumper


1972 1978 1986

1991

1994 2000 2004

2008

Quelle: Wikipedia

9

Integration AUDI A6 - Front Bumper


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

11

Example BMW


E21

E30

E36

E46

E90

Source: Wikipedia

12

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.


13

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.


14

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°


15

Color Difference Calculation


)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

16

Scaling (parametric) factors to apply the model for different purpose


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

17

Classification Rules


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

18

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


Batch Approval:

Red: visual

Green: metrological

before

after

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Effect on Batch to Batch Variation


Red: visual

Green: metrological

before

after

20

Effect on Production


before after

bumper

bodies

21

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.


22

Examples – Optimizing Color by Application and Tinting


Application

optimizing

Tinting effect

23

Example – Clearcoat Exchange


Clearcoat

Exchange

24

Example – Monitoring Bodies and Hang-on-Parts


orange: Hang-on-Part meas. by Audi

blue: Hang-on-Part meas. by Supplier

red: Production Audi

25

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.


26

Sparkle


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°.

27

Coarseness/Graininess


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


29

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°


30

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.


31

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


32

Look Up Table Tolerances for Solids AUDI95


33

Color Difference Calculation


34

Weighting Functions AUDI95


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.

35

dE Calculation Extended


36

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.


37

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?


38

Theoretical Modelling


► 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

39

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.


40

Weighting functions AUDI2000


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.

41

Weighting functions AUDI2000


110° measurement angle:

-15° measurement angle:

42

Modeling Weighting Functions AUDI2000 for Cg* <= 10


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.

43

AUDI2000 weighting functions – Flop and Chroma


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

44

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 .


45

AUDI2000 vs CIE94 – without flop term


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

46

Flop Dependence of gdL for real Metallic, Mica and Solid Shades


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

47

Comparism gdL AUDI2000 with Dupont



20 40 60 80 100

0

1

2

3

4

5


g d L

C* = 5.0 silver/gray

solid like effect

perl white

solid white

Audi2000

Dupont

48

Flop Dependence of gdC for real Metallic, Mica and Solid Shades



20 40 60 80 100

0

2

4

6


g d C

normal

solid-like

solid

reverse

49

Flop Dependence of gdH for real Metallic, Mica and Solid Shades


20 40 60 80 100

0.0

0.5

1.0

1.5

2

.0

2.5

3.0

3.5


g d H

normal

solid-like

solid

reverse

50

Weighted Color Differences


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.

51

Pass/Fail decision for Effect Colors


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

52

Classification Rules


for batch approval bodies and hang-on-parts

53

New Tolerance Model


54

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.


55

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

56

Thank you.

Documents

Colorimetric at AUDI - detroitcc.org Management at AUDI (DCC March 2012).pdf · 2 General Information on AUDI Color Management at AUDI, DCC, Detroit March 2012 Audi is a daughter