Color Theory
Introduction
Appearance is more than Color
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Color is one Aspect of Appearance
others are:
texture
gloss
reflex (flop)
opacity
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haze
45
60
Color is a Perception
Perception is affected by
Surrounding colors
What we have seen before
Food and drugs
Age
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Simultaneous Contrast
Is each circle the same color?
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Simultaneous Contrast
Is each circle the same color?
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Simultaneous Contrast
Do these designs contain
the same colors?
Are these circles
the same color?
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Successive Contrast
Stare at the white dot on the flag
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Color Communication
Humans
Variable
Poor Color Memory
General
See
Think
Instruments
Repeatable
Digital Storage
Precise
Measure
Calculate
datacolor
international
LAV
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Visual Color Evaluation - A Light Booth
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international
Primary Source
Secondary Sources
High Illumination
450
Matte, mid-tone
gray interior
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Color-Measuring Instruments
Colorimeters
Densitometers
Spectrophotometers
Goniospectrophotometers
LAV
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The actual Spectro Family
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Three Dimensions of Color
hue
chroma
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lightness
A Numerical Color Space
The CIE System
Light Sources
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Objects
Observers
Color depends on the Light Source
The same object has different colors under different lights
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Light is Energy
Our eyes detect only a small portion of the
electromagnetic spectrum
cosmic rays
uv
heat
x-rays
microwave
visible light
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tv & radio
C.I.E. Standard Illuminants
power
250
D?
200
150
D55
D65
D75
100
50
0
400 nm
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700 nm
560 nm
How Materials modify Light
diffuse
specular
reflection
regular
specular
reflection
scattering
internal
reflection
transmission
absorption
refraction
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Light - Object Interaction
An apple absorbs violet and green light
while reflecting orange and red light.
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A Spectrophotometer
LIGHT SOURCE
MONOCHROMATOR
DETECTOR
LENS
ANALOG to DIGITAL
CONVERTER
SAMPLE
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An Integrating Sphere d/8
to monochromator
specular
port
8
D65 filter
specular
illumination
light source
coating inside
sample
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Spectral Curves
This graph shows the percentage of light
reflected by the apple at each wavelength.
100%
%R
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400n
m
700nm
Six Concentrations of Blue
The shape of this spectral curve is characteristic
of a particular colorant
100
75
2
5
10
20
40
60
50
25
0
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400 nm
700 nm
A Fluorescent Yellow
Some colorants absorb ultra-violet energy and
re-emit that energy in the visible spectrum
150
125
100
75
50
25
0
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400 nm
700 nm
The Standard Observer Experiment
the experiment setup:
red, green and blue lamps with
adjustable outputs
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target color lamp
The Standard Observer Experiment
Subjects matched the target color
by adjusting red, green and blue lamps
r = ??
g = ??
b = ??
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r g b Color-Matching Functions
Experimenters found amounts of red, green and blue
lamps needed to match each color of the spectrum
0 .3 5
0 .3
0 .2 5
0 .2
0 .1 5
0 .1
0 .0 5
0
-0 .0 5
- 0 . 1Copyright 2004 Datacolor.
All rights reserved.
- - -
A Transformation: rgb to xyz
To avoid the inconveniences of calculating with
negative amounts, the rgb values were transformed
1 .8
1 .6
1 .4
1 .2
1
0 .8
0 .6
0 .4
0 .2
0
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A Second Recommendation
In 1964 CIE recommended a second
observer based on larger target areas
10
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1964
1931
The CIE Standard Observers
1964 10
1931 2
z
2
1 .5
y
1
0 .5
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A Colorimetric Description
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Color
=
Perception
Colorimetric
=
Description
CIE Tristimulus Values
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Flare
a color shift caused by a change in light source
D65
X = 31.3
Y = 20.1
Z = 6.1
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X = 47.1
Y = 27.2
Z = 2.0
Illuminant Metamerism
Metameric pairs of objects match under one condition. . .
X = 15.4
Y = 20.2
Z = 20.4
X = 15.4
Y = 20.2
Z = 20.4
35
35
30
30
25
25
20
20
15
15
10
10
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D65
Illuminant Metamerism
Metameric pairs of objects match under one condition. . .
and not under another.
X = 15.4
Y = 20.2
Z = 20.4
X = 17.2
Y = 18.5
Z = 7.00
35
35
30
30
25
25
20
20
15
15
10
10
A
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Metamerism
Four reflectance curves which yield equal tristimulus
values for D65 and the 2observer
100
X = 28.5
Y = 30.0
Z = 32.6
80
60
40
20
0
D65
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Non-Linear Transformations of xyY
Space
HunterLab (Hunter) 1942
ANLAB (Adams-Nickerson) 1950
FMCII (Friele-MacAdam's-Chickering)
CIE L*a*b* 1978
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CIELAB Color Space
+L*
+b*
C*
-a*
+a*
+h
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-b*
-L *
Munsell hues in CIE space
+b*
YR
h (hue angle)
R
+a*
-a*
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-b*
CIE Metric Chroma C*
equal C*
circles
+b*
-a*
+a*
-b*
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increasing
saturation
(chroma)
CIELAB Color Difference
da*, db*
da*
+b*
= aB - aS
dE* = (dL2 + da2 + db2)1/2
bB
batch
as
-a*
aB
db*
= bB - bS
bS
standard
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-b*
+a*
CIE LCh Color Differences
C* H*
b*
dE* = (dL2 + dC2 + dH2)1/2
CSTD dH
CBAT
dC* = C*BAT - C*STD
a*
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Tolerances: Historical Analysis
b*
Standard
Acceptable
Unacceptable
Tolerance
Limit
a*
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