Color Science 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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• Common Light Sources

Daylight

Horizon Daylight

Incandescent

Fluorescent

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• 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 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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• Viewing Geometry

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• 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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• 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 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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• 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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• 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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Questions?

Technology

Color Science Seminar