dcc sparkle and graininess tolerancing study - … dec2016 sparkle tolerancing study.pdf · dcc...
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DCC Sparkle and Graininess Tolerancing Study presented at BYK-Gardner User Meeting, October 26, 2016 Larry Steenhoek, Jeff Alspach, Allan Rodrigues
Current work on Color Difference Equations
DCC Color Education Course
2AXALTA COATING SYSTEMS PROPRIETARY
DCC Sparkle & Graininess Study
Presentation Outline
• DCC Committee Purpose and Project Background
• Experimental and Data Analysis Procedures
• Sparkle Study and Results
• Graininess Study and Results
• Findings and Future Work
• Acknowledgements
3AXALTA COATING SYSTEMS PROPRIETARY
March 2013 Sub-committee Meeting Attendees
Committee Purpose and Membership
Purpose: Upgrade SAEJ1545 with the goal of standardizing automotive industry practices for establishing color and flake appearance measurement and methodology for setting meaningful tolerances.
Membership:
Chairman: Jeff Alspach, Axalta, Mt. Clemens, MI
Car manufacturers: Audi, Ford, GM(need others)
Coatings Suppliers: AkzoNobel, Axalta, BASF, PPG
Instrument Manufacturers: BYK-Gardner, X-Rite, GTI
Includes members from ASTM, CIE, DIN
4AXALTA COATING SYSTEMS PROPRIETARY
Project Background
The BYK-mac multi-angle spectrophotometer is applied in measuring the color and flake appearance differences of automotive paints.
Overall purpose: Determine tolerance threshold for sparkle difference
Determine tolerance threshold for graininess difference
Determine inter-company differences: Do observers from a variety of companies agree with initial observations taken at Axalta?
Through industry participation, educate and raise awareness of spatial texture.
Process: Estimate sparkle and graininess difference tolerances for several colors by visual assessment, analyzing with “Binary Logistic Regression”.
6AXALTA COATING SYSTEMS PROPRIETARY
Basic Equations and Terms
Used DE94 color differences with the gonioapparent SL Lightness correction:
SL = 0.034L*; If L* ≤ 29.4., SL = 1.0
Sparkle difference dS and graininess difference dG as provided by the BYK-mac.
Definitions (ASTM E284):
Sparkle, n- The aspect of the appearance of a material that seems to emit or reveal tiny bright points of light that are strikingly brighter than their immediate surround and are made more apparent when a minimum of one of the contributors (observer, specimen, light source) is moved.
DISCUSSION—Sparkle is perceived under intense directional illumination only.
Graininess, n- for gonioapparent coatings, the perceived contrast of the light/dark irregular pattern exhibited when viewed under diffuse illumination, scale typically >100 micrometers.
DISCUSSION—Also referred to as diffuse coarseness.
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Experimental Procedures
• The panels are observed in the BYKO-Spectra Effect lightbooth.
• The viewing window on the lightbooth is shortened from 20 in. width to 5 in. width (helps focus on the center of the panels)
8AXALTA COATING SYSTEMS PROPRIETARY
Experimental Procedures
• At least 30 observers were asked to make visual assessments of sparkle or graininess difference acceptability. All of the observers had experience in judging automotive color and appearance acceptability. (Note: 30 observers were from Axalta, additional observers from several companies, hosted by Thierry).
• Panel pairs were randomly presented.
• Panels supporting board set at 45 degree, allowing viewing perpendicular to the panels with the sparkle light at 15, 45 or 75 degrees. The light intensity is adjusted to 7 (1 to 10 scale).
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Experimental Procedures
Following is an example of the process used in selecting sample pairs for sparkle visual assessments:
Used pairs of panels with known dE94 and dS measured by BYK-mac at the appropriate angle
dE94 < 1
Remaining panels
dS < 1.3 (assumes 1.3 close to 100% rejection)
Remaining panels
Choose pairs evenly spaced for:
0.30< ds <1.30, dE94 < 0.85
Remaining pairs used
(Added dS pairs close to expected high and low rejection)
10AXALTA COATING SYSTEMS PROPRIETARY
Experimental Procedures
Observers were asked:
“Ignoring any color differences, would you accept this sparkle (or graininess) difference between two adjacent car parts on your car?”
Accept, “YES”
Reject, “NO”
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Observer Data Smoothing
This process compensates for subjective variation in each observer’s assessment
Berns et al, Visual Determination of Suprathreshold Color-Difference Tolerances Using Probit Analysis. Color Res Appl 1991; 16:297-316
dSOriginal
ResponseTransform Sum of 3
IntegerDivide by
2
SmoothedResponse
Add “0” 0
1.48 Yes 0 0 0 Yes
1.57 Yes 0 1 0 Yes
1.60 No 1 1 0 Yes
1.75 Yes 0 2 1 No
1.84 No 1 2 1 No
Add “1” 1
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Binary Logistic Regression - Basics
Threshold Value at 50% Acceptance
T50=177
Goodness of Fit TestsTest DF Chi-Square P-ValueDeviance 233 206.34 0.895Pearson 233 285.85 0.010Hosmer-Lemeshow 3 12.04 0.007
Odds Ratios for Continuous PredictorsUnit of Change Odds Ratio
Sg 0.1 1.58
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Typical Visual Assessment Results
Std ID Bch ID dE94 15 OK Rej Rej Freq 15 ds
4 5 0.17 43 4 0.09 0.31
2 11 0.25 42 5 0.11 0.41
9 10 0.26 36 11 0.23 0.53
3 4 0.18 36 11 0.23 0.99
2 3 0.22 30 17 0.36 1.10
8 10 0.54 18 29 0.62 1.15
3 11 0.46 18 29 0.62 1.23
6 10 0.83 12 35 0.74 1.47
5 9 0.74 11 36 0.77 1.65
T50=1.15
A 50% frequency of rejection is the recommended tolerance
Test DF Chi-Square P-Value
Deviance 421 465.95 0.064Pearson 421 427.13 0.408Hosmer-Lemeshow 7 13.08 0.070
Unit of Change Odds RatioSg 0.1 1.31
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Binary Logistic Regression Analysis
T50=1.43
Test DF Chi-Square P-Value
Deviance 293 312.75 0.204
Pearson 293 290.92 0.523
Hosmer-Lemeshow 6 8.44 0.208
Unit of Change Odds Ratio
Sg 0.1 1.32
15AXALTA COATING SYSTEMS PROPRIETARY
Summary of Sparkle Results
Color CenterAppearance Parameter
T50 L* C*
Black dS15 (Axalta) 1.76 18.61 2.87
dS15 (Thierry) 1.78 18.61 2.87
dS15 (Combined) 1.77 18.61 2.87
dS45 (Combined) 1.43 5.04 0.60
dS75 (Axalta) 0.65 2.71 0.51
dS75 (Thierry) 0.54 2.71 0.51
dS75 (Combined) 0.60 2.71 0.51
Bright Yellow dS15 (Axalta) 1.18 77.79 59.75
dS15 (Thierry) 1.12 77.79 59.75
dS15 (Combined) 1.15 77.79 59.75
Cyber Gray dS45 (Axalta) 0.71 18.21 1.73
dS75 (Axalta) 1.03 7.48 1.56
Blue #9 dS15 (Axalta) 1.73 51.23 55.26
020
0460
.50
0.1
0
57
50
25
00
5.1
dlohserhT
*L
*C
D Scatterplot of Thr3 shold vs L* vs C*e
T50
3D Scatterplot of T50 vs L* vs C*
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Graininess Study
Graininess: Visual texture observed under cloudy day with diffused illumination
High Graininess Low Graininess
Images Courtesy of BYK-Gardner, GmbH
17AXALTA COATING SYSTEMS PROPRIETARY
Graininess Study
BYKO-Spectra Effect lightbooth: Color evaluation source at 45.
Light diffusion was enhanced with frosted plastic over light source
T50 = 0.54T50 = 1.31
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Summary of Studies To Date
NO = Color difference between available panels too large to accurately judge ds or dG
? = May be possible, no observations to-date
* Bright Yellow has too much scattering pigment to observe graininess or sparkle at other angles
ColorCenter
ds15 ds45 ds75 dGNumber of Observers
Black 30+17
Cyber Gray NO NO 31+17
Brt Yellow* NO NO NO 30+17
Blue #9 ? ? ? 28
Blue #14 ? ? ? 30
CompanyNumber of Observers
Axalta 30+3
Byk 3
Konica Minolta 1
Toyal 1
GM 2
BASF 1
Celanese 1
Keystone Aniline 1
Abedmego Environmental 2
Bosch 1
Independent Consultant 1
Total 47
Participants
19AXALTA COATING SYSTEMS PROPRIETARY
Findings
Acceptability tolerance for sparkle differences were determined for 4 colors at 15, 45, 75 degree viewing.
Observations by different groups of observers (different companies, OEMs, suppliers, etc.) were all within the predicted confidence intervals.
Some colors did not exhibit sparkle at all angles, e.g., light scatter within Bright Yellow suppresses sparkle at viewing angles greater than 15 degrees.
Some sparkle was visible when assessing graininess with the current BYK viewer, resulting in observer confusion. An additional diffuser for suppressing the sparkle worked well for graininess difference observations in this study.
Sparkle and graininess differences are difficult to assess when obvious color differences are also observed. We limited color differences between panel pairs to DE94 less than 1.0. It is very difficult to create panel sets meeting these constraints.
20AXALTA COATING SYSTEMS PROPRIETARY
Findings (Cont.)
Due to the fact visual color harmony audits are done under a variety of lighting conditions, the differences observed in our study (under controlled conditions in a light booth) might be masked or magnified in an audit.
Achieving a good correlation of visual and instrumental differences for color and spatial appearance differences can help deliver reasonable tolerances.
Over controlling instrumental assessment and under controlling visual assessments or vice versa will hinder implementation of instrumental control.
Sparkle and graininess acceptability varied by color and angle of view/measurement. Therefore tolerances need to be set accordingly.
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Future Work
• Additional visual assessments for additional sparkle angles and other metallic colors to estimate the sparkle and graininess difference tolerances.
• Explore generalized tolerances, e.g., possible relationship to color, lightness, hue, chroma, contrast, absorption vs. scattering pigmentation, etc.
• Observers often found it difficult to ignore color difference when judging sparkle or graininess differences, suggesting that assessments of color/sparkle/graininess differences are not independent of these individual components. Need industry agreement to standardize assessment when these differences are observed in combination.
22AXALTA COATING SYSTEMS PROPRIETARY
Overall Progress and needs on Specification of GonioapparentColor & Appearance
Spatial Appearance Definitions in ASTM E284 (Standard Terminology of Appearance)
? ASTM standard on visual assessment of spatial appearance
? ASTM standard on measurement of spatial appearance
? Revision of SAE J1545 (Standard for instrumental color difference measurement for exterior finishes, textiles, and colored trim) and J361 (Visual evaluation of interior and exterior automotive trim) to address sparkle and graininess
Note: Standards organizations are reluctant to standardize around instruments supplied by only one manufacturer. Can spatial appearance assessment be addressed in a generic fashion?
23AXALTA COATING SYSTEMS PROPRIETARY
Acknowledgements
BYK-Gardner for their support and providing the BYKO-Spectra Effect lightbooth for the visual assessments
Members of the DCC Committee
DCC for their sponsorship
Our colleagues in Axalta Coating Systems for their inputs and participation in visual assessments
Thierry Corporation for hosting observers in collecting additional data.
Participants from automotive companies and suppliers in on-going experiments
26AXALTA COATING SYSTEMS PROPRIETARY
Uniform Color Scales CIELAB or CIE76
222 *** baLE DDDD222 *** HCLE DDDD
2*2** baC
*)/*(tan 1 abh
222 **** CLEH DDDD
h = hue angleDH = metric hue difference
This system is more consistent withhow we perceive color
27AXALTA COATING SYSTEMS PROPRIETARY
CIE94 and CMC Equations
General Form of the Color Difference Equation
DE DL*
KL
SL
2
DC
ab*
KC
SC
2
DH
ab*
KH
SH
2
0.5
CIE94 Equation CR&A, 18, 137-139(1993)
For solid colors: SL = 1.0
For metallics: (not in CIE94
recommendation)
SL = 0.034L*; If L* <= 29.4, SL = 1.0
SC = 1 + 0.045C*ab
where C*ab is that of the standard
SH = 1 + 0.015C*ab
The parametric factors KL:KC:KH = 1:1:1
are generally satisfactory in CIE94
CMC typically uses 2:1:1
The CMC Equations
For L>16, SL
0.040975L*
10.01765L*
For L<=16, SL = 0.511
SC
0.0638Cab
*
10.0131Cab*
0.638
SH = (FT + 1 –F) SC
where
F (Cab* )4
(Cab*
)41900
0.5
T = 0.36 + abs[0.4 cos(35 + hab)] unless h is between 164˚ and 345˚ then
T = 0.56 + abs[0.2 cos(168 + hab)]
D
D
D
D
DD
HH
ab
CC
abT
HH
ab
CC
ab
LL SK
H
SK
CR
SK
H
SK
C
SK
LE
*****222
2
2
50*20
50*015.01
L
LSL
-60
-40
-20
0
20
40
60
80
100
120
-60 -40 -20 0 20 40 60 80 100 120
a*
b*
CIEDE2000
28AXALTA COATING SYSTEMS PROPRIETARY
Lightness Weighting Factor SL
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0 20 40 60 80 100 120
L*
SL
CIE 2000
CMC(1:1)
CMC(2:1)
E12.12
29AXALTA COATING SYSTEMS PROPRIETARY
AUDI 2000
ddE combined
dE AUDI 2000 CIE dE 2000
Suggested Next Step
Where fi are defined separately for L, C, H for solid or gonioapparent colors
Lex, K. & Kiggle-Bockler, Combined Color difference Method fo Multi-Angle ApplicationBYK-Gardner User Meeting, 2016
31AXALTA COATING SYSTEMS PROPRIETARY
DCC Course: Matching & Control of Metallic and Pearl Colors
Presentations by experts from different coatings companies and instrument manufacturers
Hand-on exercises reinforcing concepts, and use of spectrophotometers
Visual Match Evaluation and Colorimetry (Allan Rodrigues)
- Components of seeing color that lead to colorimetric equations
- Consistent color match terminology
- Multi-angle viewing of gonioapparent materials
- Visual exercises to reinforce understanding these concepts.
Effect Pigments for Automotive Topcoats (Claudia Royal, Axalta Coating Systems)
- Characteristics of effect pigments leading to their use
- Types of effect pigments: aluminum, mica, synthetics, multi-layer, glass, non-flake (micronized TiO2, Graphite)
- Guidelines for durable and reproducible color formulation
- Visual examples of these flakes in finishes
32AXALTA COATING SYSTEMS PROPRIETARY
DCC Course (contd.)
Impact of the Application Process on Color in Metallic/Pearl Coatings (Chris Fowler, BASF)
- Appearance properties we are looking for (gloss, DOI, no mottle, sag, craters, etc)
- Factors affecting appearance (surface roughness, coatings formulation, rheology, application)
- Application sequences (spray, flash, bake, etc), booth environment, equipment types
- Spray processes (conventional, HVLP, rotational, variables, limitations of each process)
Colorimetry Advances and Measurement of Gonioapparent Colors (Allan Rodrigues)
- Improvements on CIELAB
- Multiple angle viewing and colorimetry
- Flake characterization (sparkle, graininess) and measurement
- Setting tolerances
General Discussion (Student inputs, standards committees, DCC activities)
33AXALTA COATING SYSTEMS PROPRIETARY
Other Color Courses
Eastern Michigan University Short Course (Kendall Scott)
Instrument manufacturers provide courses
Universities provide degrees in color science as well as short 1-week courses (e.g., RIT)
Inputs on courses or 1-day workshops DCC should provide
- Paint vs. plastics color
- Exclusively on rheology and application
- Textiles – leather, thread, carpet, fabric
- How to match Bumper/Body/Parts.
- Application based class, WBBC vs. SBBC
- Matching European colors to North American colors
- Your inputs???
35AXALTA COATING SYSTEMS PROPRIETARY
CIE DE2000
DE00 DL'
kLSL
2
DC'
kCSC
2
DH'
kHSH
2
RT
DC'
kCSC
DH'
kHSH
12
G 0.5 1C ab
* 7
C ab* 7
257
L’ = L* a” = a*(1+G) b’ = b*
SL 10.015 L '50
2
20 L '50 2
SC 10.045C '
TCSH '015.01 T 1 0.17cos h '30 0.24 cos 2h ' 0.32cos 3h '6 0.20cos 4h '63
RT sin 2D RCD 30exp h '275 25
2
RC 2C '7
C '725
7
38AXALTA COATING SYSTEMS PROPRIETARY
Combined Color and Appearance Equations
CIECAM02 was developed for color imaging systems.Some use it as a color difference formula• It is the color appearance model by CIE TC8-01 (Color Appearance Modelling for
Color Management Systems)
• The model consists of:- A chromatic adaptation transform, CIECAT02 and- Equations for technically defined dimensions of color appearance: brightness (luminance), lightness, colorfulness, chroma, saturation, and hue.
• CIECAM02 inputs are the tristimulus values of the stimulus, the tristimulus values of an adapting white point, adapting background, and surround luminance information, and whether or not observers are discounting the illuminant.
Reference: Fairchild MD, Color Appearance Models: CIECAM02 and Beyond, IS&T/SID 12th Color Imaging Conference, Tutorial T1A, 11/9/04.