An overview of the science of color concepts

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3. Contents
• 1. Introductions
• 2. Light and Color Science (Light
• Source, Object and Observer)
• 3. Light and Color Measurement
• 4. Visual and Instrumental Color
• Management
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4. Light and Color
• What is Color?
ASTM E284
• color, n—(1) of an object, aspect of object appearance distinct from
form, shape, size, position, or gloss that depends upon the spectral
composition of the incident light, the spectral reflectance or
transmittance of the object, and the spectral response of the observer,
as well as the illuminating and viewing geometry.
• (2) perceived, attribute of visual perception that can be described by color
names such as white, gray, black, yellow, brown, vivid red, deep reddish
purple, or by combinations of such names.
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5. Light Source
Visible Spectrum
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6. Thank you!
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7. LIGHT AND COLOR
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8. Light and Color
• Color Perception
• 3 parts that can influence our
perception of color: Light Source Observer
1. Light source
2. Object
being
viewed
3. Observer
(person)
Object
Observer Situation
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9. Light Source
• Light
• Light is a form of energy also
known as visible light. Light is a
small portion of the
electromagnetic spectrum which
covers an extremely broad
range, from electrical and radio
waves to microwaves and
gamma rays.
• Visible light represents a very
small portion of the
electromagnetic spectrum. The
relative insensitivity of the
human eye limits the visible
portion of the spectrum to a very
narrow band of wavelengths
between approximately 380nm
to 760nm.
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10. Light Source
• Electromagnetic Spectrum
• Velocity of Light = (Wavelength) x (frequency in meters) x (cycles per second or Hertz)
» (3 x 108 m/sec)
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11. LIGHT SOURCE
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12. Light Source
• Light Energy
• White light is dispersed into its component colors by refraction.
• The angle of deviation varies with wavelength.
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13. Light Source
• Chromaticity and Color Temperature
• Color temperature is the absolute temperature T (K) which a blackbody or
perfect radiator would emit light of a certain color. The color of the emitted
light changes from red to yellow to white as the temperature increases.
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14. Light Source
• Color Temperature
20000K Blue Northwest Sky
Blue Sky with Thin White Clouds
Blue Sky
10000K
7500K high CRI 7000K North Sky
fluorescents
6000K Overcast North Sky
Short-arc Xenon
5000K
5000K high CRI
fluorescents Noon Sun
4000K
CW & CWX
3000K Deluxe Mercury
WW & WWX
Incandescent
2000K
HPS
Candle Flame
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15. Light Source
• CIE – Standard Illuminants
Illuminant Description Color Temperature
A Incandescent 2856K
B Noon Daylight 4874K
C Average Daylight 6770K
D50 Noon Sky Daylight 5003K
D65 Average North Sky Daylight 6504K
D75 North Sky Daylight 7504K
F2 Cool White Fluorescent 4230K
F11/TL84 Narrow Band Fluorescent 4000K
F12/U30 Narrow Band Fluorescent 3000K
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16. Visual Color Management
• Light Source Selection
• Use established industry procedures or standards that specify specific light
sources and viewing practices.
• Choose light sources that fit your specific application.
• Specify color temperature, SPD, CRI, CIE Assessment and lamp technology.
• Everyone must agree to use the same light sources and procedures.
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17. Visual Color Management
• Common Light Sources
Daylight Incandescent
Horizon Daylight Fluorescent
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18. Visual Color Management
• Metamerism
• Samples appear to match under daylight viewing conditions but do not match
under other lighting conditions.
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19. Instrumental Color Management
• Reflectance Curves of a Metameric Pair
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20. Visual Color Management
• Visual Color Evaluation Limitations
The reason for the use of instruments
• Visual color evaluation is subjective.
• Observers have differing color vision and color opinions.
• Color differences are difficult to quantify and communicate.
• Many variables need to be controlled including light intensity, angle of view,
surround color, light source quality etc.
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21. Visual Color Management
• Viewing Geometry
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22. Visual Color Management
• Proper Visual Color Evaluation Requires;
• Selection of the correct light source(s).
• Viewing booth must be kept clear of extra samples.
• Samples should be placed inside the light booth.
• Orient Standard and Sample in same direction, side by side, touching.
• Depending upon gloss of the samples, determine a standard viewing
geometry.
• Limit the amount of ambient light flooding the viewing booth.
• If assessor is wearing brightly colored clothing, a neutral lab coat should be
worn during assessment.
• If assessor wears glasses with tinted lenses, they should be removed for the
assessment.
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23. Visual Color Management
• What’s Wrong With This Picture?
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24. Light Source
• Color Models
• Additive Principals (Light)
blue green
red
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25. Object
• Color Models
• Subtractive Principals (Dyes and Pigments)
Magenta
Yellow
Cyan
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26. Object
• Object – Primary Types of Light Distribution
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27. Object
• Red Object
=
Red Object
Spectral Reflectance Curve
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28. Object
• Object – Spectral Reflectance Curves
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29. Object
Glossmeter Design and Use
• ASTM D523
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30. OBSERVER
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31. Light Source
• CIE Standard Observer Experiment
red sample
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32. Color Measurement
• Field of View
2o
1.7cm
50cm
10o
8.8cm
• At normal viewing distance of 50 cm (20 in.), the circle on the top represents
the 2° field on which the CIE 1931 standard observer is based. The figure at
the bottom is the 10° field on which the 1964 CIE supplementary standard
observer is based.
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33. Observer
• Facts About Color Vision
• 1 in every 12 males or 8% is color defective as a function of their
single x chromosome.
• 1 in every 250 females is color defective.
• The most common color deficiency is a partial green defective.
• Being color blind is rare, only 1 in 33,000, you would be missing all
three receptors known as Acromatopsia and the individual is called an
“Achromat”.
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34. • LIGHT AND COLOR MANAGEMENT
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35. Color Measurement
• Instrumentation
Colorimeter: Spectrophotometer:
Filter Based (3 or 4) Fixed Grating & Array
Fixed Illuminant (C/D65) Multiple Illuminant
Fixed Observer (2° or 10°) Choice of Observer
Tungsten Halogen Light Source Pulsed Xenon Light Source
No Metamerism Testing Metamerism Detection
Colorimetric Data (XYZ, L*a*b*) Spectral & Color Data
Quality Control Q.C., R&D, Formulation, etc.
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36. Light Measurement
• 3-Filter Colorimeter
Receptor section
Microprocessor
Numerical Values
x(l )sensor X = 21.21 The tristimulus values
X, Y, Z are calculated
y(l )sensor Y = 13.37 by the microprocessor
z(l )sensor Z = 9.32 and can be converted
to other colour space
Three sensors
corresponding to
Light source
under test three types of cones
in human eye
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37. Color Measurement
• Spectrophotometers
• Analyzes spectral distribution of reflected or transmitted light wavelength by
wavelength, across the visible spectrum.
• Measures the ratio of reflection or transmission by a specimen relative to a
reference standard.
CM-3700d
CM-3500d CM-2600d
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38. Color Measurement
• Integrating Sphere Geometry D8 Geometry
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39. Color Measurement
• Specular Included vs Specular Excluded Geometry
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40. Color Measurement
• SCI vs SCE Uses
SCI: SCE:
• Includes all angles of illumination • Good correlation with visual
• Measurement independent of sample assessment
surface (gloss or texture) • Characterizes effects of sample
• Measurement of true color surface
• Sample must touch the sphere • Non-contact possible, for on-line
• Widely used for color matching applications
• Values similar to 0/45, depending on
gloss level
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41. Color Measurement
• 0/45 and 45/0 Geometries
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42. Color Measurement
• Specialty Instruments – Multi Angle
Goniospectrophotometers
Face CM-512m3
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43. Color Measurement
• Developing a new color space based on what we have learned
1931 CIE Chromaticity Diagram 1976 CIE UCS Diagram
=
X = X/(X+Y+Z) u’ = 4X/(X+15Y+3Z)
y = Y/(X+Y+Z) V’ = 9Y/(X+15Y+3Z)
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44. Color Measurement
• Opponent Color Theory
black-white code
blue-yellow code
red or green code
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45. Color Measurement
• CIE L*a*b*
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46. Color Measurement
• CIE L*a*b* Values for a Red Object
• 10° Observer, Illuminant D65
L*=39.90
a*=48.04
b*=17.18
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47. Color Measurement
• CIE L*a*b* Color Difference
Trial Standard
Lighter
- = Redder
Less Yellow
• L* = 40.40 L* = 39.90 DL* = 0.50
• a* = 49.49 a* = 48.04 Da* = 1.45
• b* = 13.83 b* = 17.18 Db* = -3.35
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48. Color Measurement
• CIEL*a*b* DE*Total Color Difference
Calculation:
ΔE* = [ΔL*2 + Δa*2 + Δb*2]1/2
From previous example:
ΔE* = [(0.50)2 + (1.45)2 + (-3.35)2]1/2
ΔE* = 3.68
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49. Color Measurement
• Color Difference
• Color difference is the numerical comparison of trials to the standard.
• It indicates the difference in absolute color coordinates between a trial and a
standard.
• Differences are called Deltas (L*, a* b*).
• Deltas for L*, a* or b* may be positive or negative.
• Delta E must always be positive.
• Delta E only indicates the magnitude of a total color difference but does not
indicate how to correct it.
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50. Color Measurement
• Creating a Color Tolerance in CIEL*a*b*
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51. Color Measurement
• Creating a Color Tolerance in CIEL*a*b*
• Tolerances typically should be established for each component, DL* , Da*
and Db*.
• DE* can be used for tolerances, provided the user evaluates individual
attributes.
• These tolerances do not have to be symmetrical.
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52. Color Measurement
• CIE LCh
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53. Color Measurement
• CMC Provides for Elliptical Tolerances
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54. Color Measurement
• Creating a Color Tolerance in CMC
• CMC is based on visual acceptability.
• Key to success is the acceptability ellipsoids vary in shape and size
depending upon the color of the standard.
• CMC enables the same tolerance value (DECMC) to be used for all colors.
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55. • VISUAL AND INSTRUMENTAL COLOR MANAGEMENT
CR-10 CM-3600d
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56. Visual Color Management
• Visual Assessments
• Establish a numeric and visual tolerance that everyone can achieve
• Remember your eyes see color non-uniformly.
• Avoid global color tolerances
• Acceptable not perceptible
• Avoid submitting a “Perfect” Sample
• Avoid “Concession Color”
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57. Visual Color Management
• Color Communication
• Develop guidelines internally for consistent communication of color
assessments and directions.
• No % should be used in descriptions.
Example:
Hue descriptions - Red, Green,Yellow or Blue
Chroma descriptions - Bright or Dull
Value descriptions - Light or Dark
Adjectives - Very, Moderately or Slightly
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58. Instrumental Color Management
• Physical Standards
• Represents the target color (Ideally, in the same medium on the same
substrate)
Advantages Disadvantages
• Allows for visual comparison • May change over time
• Decreases dependency on (deterioration, handling)
absolute agreement between color • May be difficult to produce or obtain
measuring systems several pieces that match
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59. Visual and Instrumental Color
Management
• Phases of a Color Quality Program
• Design & Color Specifications
• Color Matching & Formulation
• Visual & Instrumental (Hardware/Software) Analysis
• Quality Control of the Color Manufacturing Process
• Applications Procedures & Methods
• Training & Education
• Understanding the Customers Preferences
Education and Training must be an integral part of each step within the program.
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60. Instrumental Color Management
Questions?
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