Light and Color Educational - Centasia · Communication” has helped may engineers get started...

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Light and Color Educational

Seminars and Workshops Light and color terminologies are difficult to understand and are not

main stream education curriculum. At Konica Minolta, our education

seminars and workshops are foundation to a successful color control

and management program. Our Color Education Series, “How to

Measure Color?”, “Color Control and Management” and “Precise Color

Communication” has helped may engineers get started with their color

challenges. Why Consider Color Education? • There is no unified description of color. • In-house color specifications are vague and misunderstood. • Our quality control specialists are not visually graded for color

inspection.

• The parts arriving at our plant has a wide color variance. • My supplier does not understand color specifications. • The color measurement data does not seem to agree with what

we see.

• Color control is a complicated process. • How do we measure metallic coating? • We need to setup a color control workflow.

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Tel: (662)361-3730

http://www.centasiathai.com/ or

Write to us at [email protected]

1

Understanding

Your Guide to Instrumentation

COLOR

Color PerceptionBasic Elements

A Light Source

An Object

An Observer

Factors Affecting PerceptionLight Source Differences

Daylight Tungsten Fluorescent

Factors Affecting PerceptionObserver Differences

2

Less Vivid

More Vivid

Factors Affecting PerceptionSize Differences

Lighter? Darker?

Factors Affecting PerceptionBackground Differences

Before Sanding (Glossy) After Sanding (Dull)

Sandpaper

Factors Affecting PerceptionSurface Condition Differences

Daylight

Sample

Observer

Factors Affecting PerceptionDirectional Differences

3

Sample 1 Sample 2

Factors Affecting PerceptionColor Memory

Observer

Which sample is a darker red?

= BLUE

Color Matching FunctionThe Human Eye

Retina

Color Vision Light is not a color in itself.

It is the radiant energy from light that stimulates the retina in the eye.

This produces a sense of sight where the concept of color is formed and the brain reacts to it.

Among the colors of the spectrum, red, green and blueare described as the primary colors.

Our eyes can perceived color because the eye has three types of cones which are sensitive to these 3 primary colors.


Retina - Rods and Cones.

Cones - Respond to colors. There are three different types of cones.

S – 420 to 440 nmM – 530 to 540 nmL – 560 to 580 nm

Rods - For vision in very dim light but do not impart color vision.

Note : The colors that we see are the result of different x, y and z proportions (stimuli) in the light received from an object.


4

Photopic Vision- Where the Cones are active and normal color vision is possible when the luminance level is above 3 cd/m2.

Scotopic Vision- Where the Rods are active and no color vision is possible when the luminance level is below 0.05 cd/m2.

Mesopic Vision- Vision at luminance level in between the scotopic and photopic. The ability to distinguish color decreases as the lighting level decreases.

Rods

Cones


Spectral Sensitivity Curves corresponding to the human eye

X has a high sensitivity in the red wavelength region Y has a high sensitivity in the green wavelength region Z has a high sensitivity in the blue wavelength region

Color Matching FunctionSensitivity Curves

The CIE XYZ values are not the S,M,L responses of the human eye but rather a set of tristimulus values called XYZ which are roughly red, green and blue

Note that XYZ are not physically observed red, green and blue colors. Rather they may be thought of as derived parameters from the red, green and blue colors.

The CIE XYZ color space was derived from a series of experiments done in the late 1920s by W. David Wright and John Guild. Their experimental results were combined into the specification of the CIE RGB color space, from which the CIE XYZ color space was derived

Color Matching FunctionSensitivity Curves

The CIE tri-stimulus values X, Y and Z of a color are obtained by multiplying together

- the Spectral Power Distribution of a CIE standard illuminant- the Spectral Reflectance (or the transmittance) of the object and - the Color Matching Functions x(λ), y(λ) and z(λ) .

The products are summed up for all the wavelengths in the visible spectrum to give the tri-stimulus values.

x x=

XYZSpectral Power

Distributionof illuminant

Color Matching Functions

Spectral Reflectanceof specimen

Color Data

5

CIE X Tristimulus

CIE Z Tristimulus

X = 41.9

Y = 37.7

Z = 8.6

CIE Z Tristimulus

CIE Illuminant D65

X

Reflectance

=

CIE x Observer

CIE z Observer

X

X

X

CIE y Observer

CIE z Observer

=

=

=

CIE x Observer-

-

-

Color Data

X = 41.9 Z = 8.6Y = 37.7

CIE Y TristimulusCIE Y Tristimulus

CIE X TristimulusL*a*b* Color Space (CIELAB)

Lightness L*L* = 116 ( Y ) ⅓ - 16

Yn

Chromaticity a* and b* a* = 500 [ ( X ) ⅓ - ( Y ) ⅓ ]

Xn Yn

b* = 200 [ ( Y ) ⅓ - ( Z ) ⅓ ]Yn Zn

X, Y, Z : Tristimulus values XYZ for 2 deg standard observer

Xn, Yn, Zn : Tristimulus values XYZ for 2 deg standard observer of a perfect reflecting diffuser.

Color Data

Color Data

300 450 550 650 1000

VISIBLE SPECTRUM INFRAREDULTRAVIOLET

0

50

100

150

360 500 600 780

Wavelength - Nanometers [nm]

RelativeEnergy

Daylight

Visible SpectrumLight

6

The light given off by a light source (illuminant) as well as light reflected by an object (reflectance) can be measured with instruments in terms of its spectral characteristics (spectrophotometery).

406080100

%

700400 500 600nm

700Wavelength (nm)

Reflectance (%)

Spectral Characteristics (% / nm)

Spectral Data

400nm 700nm

400nm 700nm

400nm 700nm

Re

flec

tan

ceR

efl

ecta

nce

Re

flec

tan

ce

Wavelength

Wavelength

Wavelength

0

0

0

100

100

100

White

Black

Grey

Spectral Data

Spectral DataSpectrophotometric Curve for Yellow

Wavelength – [Nanometers]

% R

ela

tive

Re

flec

tan

ce

400 500 600 700

0

25

50

75

100

COMMISSION INTERNATIONALE DE L’ECLAIRAGEINTERNATIONAL COMMISSION ON ILLUMINATIONINTERNATIONAL BELEUCHTUNGSKOMISSION

As its name implies, the International Commission on Illumination - abbreviated as CIE from its French titleCommission Internationale de l’Eclairage - is an organization devoted to international cooperation andexchange of information among its member countries on all matters relating to the science and art oflighting. The CIE is an autonomous organization. It is not appointed by any other organization political orotherwise but has grown out of the interests of individuals working in illumination. Since its inception, theCIE has been accepted as representing the best authority on the subject and as such is recognized by theISO as an international standardization body.

Central Bureau : Kegelgasse 27 A-1030 Wien AustriaPhone : (43 1) 714 31 87/0 Fax : (43 1) 713 08 38/18

Email : [email protected]

CIE

7

The International Commission on Illumination (CIE) is the international authority on light, illumination, color and color spaces.

Established in 1913 is today based in Vienna, Austria.

Seven divisions

1 - Vision & Color

2 - Measurement of Light and radiation

3 - Interior Environment and Lighting Design

4 - Lighting & Signaling for Transport

5 - Exterior Lighting & Other Applications

6 - Photobiology & Photochemistry

7 - Image Technology

CIE

First we need to:

• Standardize the Light Source (Illuminant)

• Standardize the Observer

• Standardize the Measurement Method

• Standardize the Color System

How To Quantify Color

D65 6504 K CIE Standard Illuminant D65 representing average daylight including ultraviolet radiation

D50 5003 K CIE Standard Illuminant D50 representing daylight including ultraviolet radiation

C 6774 K CIE Standard Illuminant D65 representing average daylight including ultraviolet radiation

A 2856 K CIE Standard Illuminant A representing an incandescent lamp

F2 4230 K CIE Fluorescent Illuminant F2 representing a cool white fluorescent lamp

F6 4150 K CIE Fluorescent Illuminant F6 representing a cool white fluorescent lamp

Name Color Temp Description

CIE Standard Illuminants

F7 6500 K CIE Fluorescent Illuminant F7 representing a daylight fluorescent lamp

F8 5000 K CIE Fluorescent Illuminant F8 representing a daylight white fluorescent lamp

F10 5000 K CIE Fluorescent Illuminant F10 representing a three band daylight white fluorescent lamp

F11 4000 K CIE Fluorescent Illuminant F11 (DIN TL-84) representing a three band white fluorescent lamp

F12 3000 K CIE Fluorescent Illuminant F12 representing a three band warm white fluorescent lamp (Ultralume 3000)

CIE Standard IlluminantsName Color Temp Description

8

Spectral Power Distribution Graph is a plot of the relative power of the light source against the wavelength. This can be measured using a Spectroradiometer CS-2000.

Co-related Color Temperature of a light source is the temperature of the blackbody when heated to a certain temperature to give the color of the light source.

White Lamp Green Lamp Red Lamp

2856 K 4230 K 6504 KBlack Body

Tungsten Fluorescent DaylightHeat Source


Blackbody is an idealized physical body that absorbs all incident electromagnetic. Because of this perfect absorption at all wavelengths, it is also the best emitter of thermal radiation.

All matter emits electromagnetic radiation when it has a temperature above absolute zero. The radiation represents a conversion of a body's thermal energy into electromagnetic energy, and is therefore called thermal radiation.

An object that absorbs all radiation falling on it, at all wavelengths, is called a black body.


As the temperature increases past a few hundred degrees Celsius, black bodies start to emit visible wavelengths, appearing red, orange, yellow, white, and blue with increasing temperature.

The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source.

Color temperature is conventionally stated in the unit of absolute temperature, the kelvin, having the unit symbol K.


The spectral power distribution or relative power at each wavelength fortypical daylight (Judd 1964, CIE1971)

The spectral power distribution of blackbodies with color temperatureof 2854K (Source A) and 6500K (Pivovonski 1961). (The curves areadjusted to a relative power of 100 at 560 nm.

Typical Daylight

Tungsten Filament Lamp

Daylight D65

Tungsten A


9

The spectral power distribution of a typical linesource, a mercury arc lamp (IES 1981).

The spectral power distribution of a cool whitefluorescent lamp (IES 1981).

Mercury Arc Lamp

Cool White Fluorescent Lamp

CIE Standard Illuminants CIE Standard Illuminants

Standard Illuminant A( 2856 K )

Standard Illuminant C( 6774 K )

Standard Illuminant D65( 6504 K )

2 Degree Standard Observer

The average human chromatic response views through a 2° angle, due to the belief that the color-sensitive cones resided within a 2° arc of the fovea.

The fovea is responsible for sharp central vision (foveal vision), which is necessary in humans for:

• Reading

• Watching TV or movies

• Driving

• Any activity where visual detail is of primary importance.

CIE Standard Observer

10 Degree Standard Observer

A more modern alternative is the CIE 1964 10 ° Standard Observer, which is derived from the work of Stiles and Burch and Speranskaya.

For the 10° experiments, the observers were instructed to ignore the central 2° spot. The 1964 Supplementary Standard Observer is recommended for more than about a 4° field of view.


10


At normal viewing distance of 50cm, the circle on the top represents the 2° field onwhich the CIE 1931 standard observer is based.

The figure on the bottom is the 10° field on which the 1964 CIE supplementarystandard observer is based.

The color matching functions x, y, z of the 1931 CIE standard observer and x10, y10, z10 of the 1964 CIE supplementary standard observer are compared here (data from CIE 1974). These sets of tristimulus values of the spectrum color, defining the 1931 CIE standard observer and the 1964 CIE supplementary standard observer, respectively, in terms of the same X, Y and Z primaries are a little different. Most significantly, y10 is not the same as y or V().


x()y()

z()

RED

GREEN

BLUE

X = 21.21

Y = 13.37

Z = 9.32

BLUE

MICRO-COMPUTER

MICRO-COMPUTER

BRAIN

Visual Method:

Colorimetric Method:

Spectrophotometric Method:

X

Y

Z+

EYE

X = 21.21

Y = 13.37

Z = 9.32

Measurement Methods

CO

NES

TH

REE

SEN

SOR

SSP

ECTR

AL

SEN

SOR

S

RED

GREEN

BLUE

X

Y

Z+

Reflectance Measurement

Color measurement of a sample based on the light reflection from the surface of the sample.

Light source and sensor are on the same side.

Transmittance Measurement

Color measurement of a sample based on the light transmitted through the sample.

Light source and sensor are on the opposite side.

Trans-Reflectance Measurement

Color measurement of a sample based on the light transmitted through the sample.

Light source and sensor are on the opposite side.

Measurement MethodsInstrumentation

11

X

Y

Z+

Opaque Solid Samples

Plastic

Metal

Fabric

Paper

Opaque Granular Samples

Resin

Powder

Granules

Opaque Paste Samples

Cream

Sauce

Measurement MethodsReflectance Application

Portable or Benchtop

Chroma Meter

Spectrophotometer

Different Target Mask Size

Small : 3 or 4 mm

Medium : 8 mm

Large : 25.4 or 30 mm

White Calibration Plate

Standard accessory with instrument

Petri Dish & Cells

Measurement MethodsReflectance Requirement

+

Transparent Solid Samples

Plastic Film / Plate

Glass

Transparent Semi-Solid Samples

Jelly

Gel

Transparent Liquid Samples

Chemicals

Beverages

Measurement MethodsTransmittance Application

Measurement MethodsTransmittance Requirement

Benchtop Spectrophotometer

With transmittance chamber

CM-5, CM-3600A, CM-3700A

Large Target Mask

30mm

25.4mm


Standard accessory

Zero Calibration Plate

Optional accessory

12


Transmittance Specimen Holder

Optional accessory

Cell Type

Quartz Glass

Acrylic Plastic

Cell Size

20mm

10mm

2mm


10mm Cell Transmittance Holder

Optional accessory

Cell Type

Quartz Glass

Cell Size

10 x 10mm

10 x 20mm

10 x 50mm

X

Y

Z+

Measurement MethodsTrans-Reflectance Application

Translucent Samples

Hazy Plastic

Hazy Glass

Measurement MethodsTrans-Reflectance Requirement

Portable or Benchtop

Chroma Meter

Spectrophotometer

Various Target Mask

3mm or 4mm (Small)

8mm (Medium)

25.4mm or 30mm (Large)


Standard accessory

White Tile Backing

13

B

Spectral reflectance of metameric objects are different Tristimulus values are the same under one light but different under another Problem is due to the use of different pigments and materials Color Instruments will display metamerism index (MI) to indicate the extent of the changes

A AB B

Fluorescent Lamp (F2) Tungsten Lamp (A)

Metamerism

Whiteness Index (ASTM E 313), Whiteness Index (CIE)

Yellowness Index (ASTM E 313), Yellowness Index (ASTM D 1925)

Blue Reflectance (ASTM E 313)

Dominant Wavelength, Excitation Purity

CMC

FMC2

ANALab

Chromatic Strength

Tappi Brightness

Opacity

Apparent Strength

∆E at Equal Apparent Strength

Metamerism Index

ISO Crock and Gray Scale

Color Notations

Color Measuring InstrumentHow to Make Selection

Color Meter or Spectrophotometer

Reflectance or Transmittance

Benchtops or Portables

Geometry: d/8, d/0, 45/0, 0/45

Measuring Area: 3mm, 8mm, 30mm

Specular Component: SCI or SCE

Standard Illuminant: D65, A, F2, etc…

Standard Observer: 2° or 10°

Instrument GeometryReflectance Measurement

D/8 Geometry

Diffused illumination / 8° Viewing

D/0 Geometry


8°

Sample

Xeon Lamp

Sensor

Xeon Lamp

Sensor

Sample

0°

Integrating Sphere

Integrating Sphere

14

Instrument GeometryReflectance Measurement

Sensor SensorXeon Lamp

Sample

Sensor

XeonLamp

Xeon Lamp45° 45°

Sample

45° 45°

0/45 Geometry

0° illumination / 45° Viewing

45/0 Geometry


TransparentSample

Sensor

TransparentSample

SensorLamp

Lamp

Instrument GeometryTransmittance Measurement

0/0 Geometry


d/0 Geometry


Specular Light - Light reflected directly opposite the incident lightDiffuse Light - Light that are scattered in many directions Total Reflectance - Specular Reflectance + Diffuse Reflectance

IncidentLight

DiffuseLight

SpecularLight

Sample

Specular Component

Xeon Lamp

Sensor

Specular component escapes through the light trap. Sensor captures only the diffuse component. Correlates to the way an observer sees the color of a sample. This is known as SCE condition.

Light TrapOpened

Sample

Integrating Sphere

Specular ComponentExcluded (SCE)

15

Xeon Lamp

Light TrapClosed

Sample

Sensor

Integrating Sphere

Specular ComponentIncluded (SCI)

Specular component is trapped within the integrating sphere. Sensor captures both the diffuse and specular component. Measures the total color appearance independent of the surface conditions. This is known SCI condition.

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