light and color educational - centasia · communication” has helped may engineers get started...
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Giving Shape to Ideas
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.
Call Us Many manufacturers and their supply chain have benefited from our
Color Education Series. Let us help you color your world. Visit our learning center for more information at
Centasia Co.,Ltd
Bangna Thani Tower-10th Floor, suite A1-A2
1/20 Soi Bangna-Trad 34, Bangna-Trad Hwy Km.3, Bangna, Bangkok
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.
Color Matching FunctionThe Human Eye
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.
Color Matching FunctionThe Human Eye
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
Color Matching FunctionThe Human Eye
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
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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
CIE Standard Illuminants
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.
CIE Standard Illuminants
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.
CIE Standard Illuminants
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
CIE Standard Illuminants
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.
CIE Standard Observer
10
CIE Standard Observer
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().
CIE Standard Observer
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
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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
White Calibration Plate
Standard accessory
Zero Calibration Plate
Optional accessory
12
Measurement MethodsTransmittance Requirement
Transmittance Specimen Holder
Optional accessory
Cell Type
Quartz Glass
Acrylic Plastic
Cell Size
20mm
10mm
2mm
Measurement MethodsTransmittance Requirement
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)
White Calibration Plate
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
Diffused illumination / 0° Viewing
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
45° illumination / 0° Viewing
TransparentSample
Sensor
TransparentSample
SensorLamp
Lamp
Instrument GeometryTransmittance Measurement
0/0 Geometry
0° illumination / 0° Viewing
d/0 Geometry
Diffused illumination / 0° Viewing
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.