color seminar
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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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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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Light Source
Visible Spectrum
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Thank you!
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LIGHT AND COLOR
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Light and Color
• Color Perception• 3 parts that can influence our
perception of color:
1. Light source
2. Object being viewed
3. Observer (person)
Observer Situation
Light Source Observer
Object
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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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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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LIGHT SOURCE
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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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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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• Color Temperature
Light Source
Candle Flame
Deluxe Mercury
Noon Sun
Blue Northwest Sky
Blue Sky with Thin White Clouds
Incandescent
North Sky
Blue Sky
7500K high CRI fluorescents
Short-arc Xenon
5000K high CRI fluorescents
CW & CWX
WW & WWX
HPS
Overcast North Sky
20000K
10000K
7000K
6000K
5000K
4000K
3000K
2000K
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Light Source
• CIE – Standard Illuminants
Illuminant
ABC
D50D65D75F2
F11/TL84F12/U30
Description
IncandescentNoon Daylight
Average DaylightNoon Sky Daylight
Average North Sky DaylightNorth Sky Daylight
Cool White FluorescentNarrow Band FluorescentNarrow Band Fluorescent
Color Temperature
2856K4874K6770K5003K6504K7504K4230K4000K3000K
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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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Visual Color Management
• Common Light Sources
Daylight
Horizon Daylight
Incandescent
Fluorescent
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Visual Color Management
• Metamerism
• Samples appear to match under daylight viewing conditions but do not match under other lighting conditions.
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Instrumental Color Management
• Reflectance Curves of a Metameric Pair
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Visual Color Management
• Visual Color Evaluation LimitationsThe 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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Visual Color Management
• Viewing Geometry
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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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Visual Color Management
• What’s Wrong With This Picture?
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Light Source
• Color Models• Additive Principals (Light)
blue green
red
• Color Models• Subtractive Principals (Dyes and Pigments)
Magenta
Yellow
Cyan
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Object
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Object
• Object – Primary Types of Light Distribution
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• Red Object
Object
Red Object
Spectral Reflectance Curve
=
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Object
• Object – Spectral Reflectance Curves
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Object
Glossmeter Design and Use• ASTM D523
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OBSERVER
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Light Source
• CIE Standard Observer Experiment
red sample
• Field of View
• 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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Color Measurement
22oo
1010oo
50cm
1.7cm1.7cm
8.8cm8.8cm
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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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• LIGHT AND COLOR MANAGEMENT
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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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Light Measurement
• 3-Filter Colorimeter
x(l )sensor
y(l )sensor
z(l )sensor
Three sensors corresponding to three types of cones in human eye
X
Y
Z
= 21.21
= 13.37 = 9.32
Microprocessor Receptor section
Light source under test
Numerical ValuesThe tristimulus values X, Y, Z are calculated by the microprocessor and can be converted to other colour space
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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-3500d
CM-3700d
CM-2600d
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Color Measurement
• Integrating Sphere Geometry D8 Geometry
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Color Measurement
• Specular Included vs Specular Excluded Geometry
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Color Measurement
• SCI vs SCE Uses
SCI: • Includes all angles of illumination • Measurement independent of sample surface (gloss or texture) • Measurement of true color • Sample must touch the sphere • Widely used for color matching
SCE: • Good correlation with visual assessment • Characterizes effects of sample surface • Non-contact possible, for on-line applications • Values similar to 0/45, depending on gloss level
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Color Measurement
• 0/45 and 45/0 Geometries
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Color Measurement
• Specialty Instruments – Multi AngleGoniospectrophotometers
Face CM-512m3
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Color Measurement
• Developing a new color space based on what we have learned1931 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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Color Measurement
• Opponent Color Theory
blue-yellow code
black-white code
red or green code
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Color Measurement
• CIE L*a*b*
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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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Color Measurement
• CIE L*a*b* Color Difference
• 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
LighterRedderLess Yellow
Trial Standard
- =
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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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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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Color Measurement
• Creating a Color Tolerance in CIEL*a*b*
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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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Color Measurement
• CIE LCh
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Color Measurement
• CMC Provides for Elliptical Tolerances
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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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• VISUAL AND INSTRUMENTAL COLOR MANAGEMENT
CM-3600dCR-10
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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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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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Instrumental Color Management
• Physical Standards• Represents the target color (Ideally, in the same medium on the same
substrate)
Advantages• Allows for visual comparison• Decreases dependency on absolute agreement between color measuring systems
Disadvantages• May change over time (deterioration, handling)• May be difficult to produce or obtain several pieces that match
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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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Instrumental Color Management
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