colorimetry and its application - bob chung
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Colorimetry and Its Application 1
Colorimetry and Its Application R. Chung, Professor
Colorimetry has become more and more useful in graphic arts imaging for color specification, process control, and quality assurance.!
(Rev._2015)!
Copyright 2015 RIT – May not be reproduced without permission
Topics Covered
Light, object, and color vision
Tristimulus integration – 1931 CIEXYZ color space – 1976 CIELAB color space
Color matching and color difference
Colorimetry application
2
Colorimetry and Its Application 2
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Light and Color
Light exists as a form of energy.
Color is a visual sensation.
Visual sensation requires – Light – Object – Observer
Brain
3
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Human Color Vision
Color perception is complex. – Even if we standardize the lighting condition, the color of the
same object may be perceived differently by two people. - Perception is influenced by age, sex, cultural experiences
CIE colorimetry standardizes how we measure color. – Color measurement may be able to predict color perception.
4
Colorimetry and Its Application 3
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Color Vision Tests
Ishihara�s test for color blindness
Farnsworth-Munsell 100 Hue test
5
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Color Vision Deficiency
Anomalous trichromats
Statistics – 7% of male population have color vision defects – Less than 0.5% of female population have color vision defects
normal deutan" tritan"
6
Colorimetry and Its Application 4
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Standard Observer
In 1931, CIE defined a set of mathematical functions which describe the sensitivity of the eye. – Based on two independent color matching experiments by
Wright and Guild - To quantify how spectrum colors are matched rather than to specify
a color sensation
7
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Color Matching Experiment
Three imaginary primaries (R, G, B) were used in the color matching experiments.
8
Colorimetry and Its Application 5
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1931 2o Standard Observer
The amount of tristimulus values required to match the equal-energy spectrum
600400 500 700
trist
imul
us v
alue
s
0
0.5
1.0
1.5
2.0
2.5
x-
z-
y-
wavelength (λ)
Mathematics is used to transform color matching functions (x-bar, y-bar, z-bar) without negative portion.!
9
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Rods & Cones Distribution
Color vision is centered around 2-degree fovea where cones are heavily concentrated.
Source: Leo Hurvich!Professor of Psychology!
Univ. of Pennsylvania !
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Colorimetry and Its Application 6
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Supplementary Observer
A CIE 10o standard observer was established in 1964. – Larger visual field was used for color matching.
- Suitable for paint, textile, and plastics applications
Arm length
Thumb up4 degrees
2"
28"
11
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Spectral Power Distribution
SPD is measured by a spectroradiometer. – Color temperature describes the hue of the light source.
- Lamps with D50 color temperature can be different in spectral energy distribution.
– A potential problem of metamerism
– CRI describes its color rendering capability. - How complete spectral energies are across the visible spectrum
12
Colorimetry and Its Application 7
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CIE Standard Illuminants
Illuminant A – Tungsten – 2800oK
Illuminant D50 – Daylight – 5000oK
0
50
100
150
200
250
390
410
430
450
470
490
510
530
550
570
590
610
630
650
670
690
Wavelenght (nm)
P
700
Illuminant A
0
20
40
60
80
100
120
390
410
430
450
470
490
510
530
550
570
590
610
630
650
670
690
Wavelenght (nm)
P
Illuminant D50
700
Source:!Hunt, R.W.G, Measuring Colour (2nd edition, 1991)!
13
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CIE Standard Illuminants
SPD of F2 at 5 nm intervals (blue) shows spikes on top of the continuous emission. – SPD of F2 at 10 nm intervals (red line) does not have sufficient
resolution to show the spikes.
14
Colorimetry and Its Application 8
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Object Color
Measured by a spectrophotometer – A spectrophotometer measures the reflectance of a sample at
many points across the visible spectrum.
15
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Spectrophotometer
Instrument design parameters – Geometry
- 0 / 45 – Measuring diffuse reflectance
- Integrating sphere – Specular component included or excluded
– Monochrometer - Grating - Interference filters
– Measurement spot size
16
Colorimetry and Its Application 9
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Tristimulus Integration
ISO 13655 (2009) – R(λ) is the reflectance factor at λ.
– WX(λ) is the weighting factor at λ for tristimulus value X.
– WY(λ) is the weighting factor at λ for tristimulus value Y.
– WZ(λ) is the weighting factor at λ for tristimulus value Z.
17
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XYZ-based TVI (ISO/TS 10128)
Magenta and black
Yellow
Cyan
€
TVI =100 Yp −YtYp −Ys
#
$ %
&
' ( − InputTV
€
TVI =100 Zp − ZtZp − Zs
#
$ %
&
' ( − InputTV
€
TVI =100 Xp − 0.55Zp( ) − Xt − 0.55Zt( )Xp − 0.55Zp( ) − Xs − 0.55Zs( )
#
$ % %
&
' ( ( − InputTV
Subscripts p: paper t: tint s: solid
18
Colorimetry and Its Application 10
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Measuring Tristimulus Values
Spectro-colorimeter – Computationally derived with spectral data
- ANSI CGATS.5 - 1993 - Suitable for critical color communication
Filter-colorimeter – Derived by means of optical integration with the light-filter-
detector combination - Spectral data are not used
19
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Color Space Models
CIE Chromaticity coordinates, Yxy – Y is the lightness of the color – x represents fractional redness – y represents fractional greenness
- z or (1-x-y) is the fractional blueness
• x = XX + Y + Z
• y = YX + Y + Z
x
y
20
Colorimetry and Its Application 11
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Chromaticity Diagram
Spectrum colors form a horse shoe shaped locus. – Dominant wavelength – Purity
x
y
Y
Ill. D65C1
Dominatewavelength
700 nm
525 nm
400 nm
575 nm
o500 nm
21
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CIE Color Naming
Different wavelength region represents color names of different hues.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8x
y
CIE spectrum locus
700600
575
550
525
500
475
450400
Green
Yellow
Yellowishgreen
Greenishyellow
PinkWhite
OrangeReddishorange
Red
Blue
Bluishgreen
Greenishblue
Purple
Purplishred
Reddishpurple
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Colorimetry and Its Application 12
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Color Gamut Comparison
A printer�s CMYK color gamut is different from a monitor�s RGB color gamut.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8x
y G
C
B
M
R
Y
CIE spectrum locus
700600
575
550
525
500
475
450400
Monitor
Printer
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Uniform Color Space
MacAdam ellipses – Equal visual difference should be plotted with equal distance.
- Chromaticity diagram - did not do well.
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Colorimetry and Its Application 13
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1976 CIELAB Color Space
Opponent color theory – L* is lightness – a* is redness or greenness
- Redness (if a* is positive) - Greenness (if a* is negative)
– b* is yellowness or blueness - Yellowness (if b* is positive) - Blueness (if b* is negative)
-a* +a*+b*
-b*
Black
WhiteYellow
Blue
RedGreen
L*
25
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XYZ-to-Lab Formulas
ISO 13655
L* = 116[f(Y/Yn) – 16!!a* = 500[f(X/Xn) – f(Y/Yn)]!!b* = 200[f(Y/Yn) – f(Z/Zn)]!!X, Y, Z are the tristimulus values!Xn, Yn, Zn are the white point !
26
Colorimetry and Its Application 14
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Process Inks
Real inks have incomplete reflection and absorption. – CIELAB is used to specify the ink color.
- Sample preparation - Measurement conditions
600400 500 700
20
40
60
80
100
% R
efle
ctan
ce
cyan
yellow
magenta
wavelength (λ)
Ink CIELAB (D50/2)Patch L* a* b*Cyan 60.5 -44 -41.1Magenta 55.7 63.2 0.3Yellow 88.7 3.2 96.3Black 10 0.4 3.8
27
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CIE LCh Color Space
The vector equivalent of the CIELAB color space – Metric chroma
– Hue angle
+a*-a*
+b*
-b*
C*oh
•
C* = a*2 + b*2
h = tan-1 b*a*
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Colorimetry and Its Application 15
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Hue Angle Calculations
Given a* (cell D17) and b* (cell E17) – Hue angle in radian (cell H17)
- =IF(ATAN2(D17, E17)>=0,ATAN2(D17,E17), - 2*PI()+ATAN2(D17,E17))
– Hue angle in degrees=DEGREES(H17)
29
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Munsell Color Space
Based on visual judgment – Hue – Value – Chroma
Notation: 5R 5/10
Value ChromaHue
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Colorimetry and Its Application 16
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Device Dependent Color
Computer graphics color space – RGB
Designers color space – Swatchbook
Printer color space – CMYK
31
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Device Independent Color
Act as a reference color (profile connection) space in color management systems
Trumatch
Focoltone
CIEReference
Color Space
RGB1
RGB2Pantone
SWOP
CMYK
HSL
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Colorimetry and Its Application 17
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Color Matching
Invariant (or spectral) match – When two colors have the same spectrophoto-metric curves
(SPC), they will have the same tristimulus values. - Their match is invariant
- If (SPC)1 = (SPC)2, then (XYZ)1 = (XYZ)2
33
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Color Matching
Metameric (conditional) match – When two colors have different spectrophoto-metric curves, but
have the same tristimulus values - The color match is conditional. - The two objects are metamers.
- (XYZ)1 = (XYZ)2, but (SPC)1 ≠ (SPC)2
34
Colorimetry and Its Application 18
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Color Difference
For any two colors, – C 1: L 1*, a 1*, b 1* – C 2: L 2*, a 2*, b 2* – ∆E is the total color difference
ΔE = L1* - L2
* 2 + a1
* - a2* 2
+ b1* - b2
* 2
a*
L*
b*C2
C1
•
•∆E
∆E is the abbreviation for �Empfindung� in German, i.e., sensation.
35
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Color Difference
∆L*, ∆a* and ∆b* expressed as human visual sensation – Between a sample and a reference – (sample-reference)
When ∆L* is '+' Lighter ∆L* is '-' Darker ∆a* is '+' Redder or less green ∆a* is '-' Less red or greener ∆b* is '+' Yellower or less bluer ∆b* is '-' Less yellow or bluer
The Sample is
36
Colorimetry and Its Application 19
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Color Difference as a Number
Spot colors and trademark colors need to be matched closely. – Small color difference is allowed
∆E Perception Interpretation< 1 No difference Excellent match1~2 Just noticeable Good match4~6 Noticeable Fair match> 9 Strong difference Poor match
37
∆E Magnitude, Perceptibility, and Acceptability
Printing tolerances -- process inks
0
2
4
6
8
10
∆ E
Strong difference
Noticeable
Just noticeableNo difference
12
14
16
Instrument error
Ink verification
Printing tolerances -- single ink
Color imagereproduction analysis -- original vs. repro
18
As interpreted as a simple field
Perceptibility!Acceptability!
38
Colorimetry and Its Application 20
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Color Tolerance as a Volume
Three color tolerancing models – ∆L*, ∆a*, and ∆b* form a rectangular box. – ∆L*, ∆C*, and ∆hab* form a wedge. – CMC takes on an ellipsoidal-shaped volume.
39
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CMC Tolerancing
The eye is better at detecting hue differences in the orange than in the green.
The eye is more sensitive to low chroma difference than high chroma difference.
The eye has greater acceptance for shifts in the lightness (l) than in the chromaticity (c) dimension.
40
Colorimetry and Its Application 21
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Summary
Color is a visual sensation. – Light, object, and human vision are involved.
Tristimulus integration is the basis for color measurement. – CIELAB color space is the language for color specifications.
Color matching is possible between metamers. – Color difference is useful for determining acceptability.
41
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Colorimetry Application
Material specifications – How inks are specified and compared
Process characterization – How color gamut, color variations, and RGB-to-CMYK
conversion are specified
Color matching and image reproduction – ∆E matters to color matching. – ∆E does not matter to pleasing pictorial color image
reproduction.
42
Colorimetry and Its Application 22
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Material Specifications
Colorimetric properties of halftone tints – Cyan screen tints
Colorimetric differences – Rubine ink & rhodamine ink
Colorimetric specifications – Standardized printing inks for offset lithography
- ISO 2846
43
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Colorimetric Properties
Cyan halftone tints – Four levels of dot area coverage
- 25%, 50%, 75%, & solid
0
10
20
30
40
50
60
70
400 450 500 550 600 650 700
Wavelength
C25C50C75C100
% R
efle
ctan
ce
max. absorption!— Their SPCs are non-crossing!— The wavelength of the max. ! absorption is at 630 nm!
• The SPC of the solid patch is situated in the bottom.!
44
Colorimetry and Its Application 23
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Colorimetric Properties
Cyan halftone tints
— Tints have similar hue angle! in the a* b* diagram as the" solid, but differ in metric! chroma (C*)!− When solid IFT increases," hue shift may result – the" mass tone effect.!
b*!
-50!-40!-30!-20!-10!
0!10!20!30!40!50!
-50! -40! -30! -20! -10! 0! 10! 20! 30! 40! 50!
a*!•!
•!•!•!
50%!
100%!
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Colorimetric Differences
Two magenta inks – Rubine is a reddish magenta ink.
- Cost cheaper – Rhodamine a bluish magenta ink.
- More expensive
0
10
20
30
40
50
60
70
80
90
100
400 450 500 550 600 650 700
Wavelength (nm)
RubineRhodamine
% R
efle
ctan
ce
46
Colorimetry and Its Application 24
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Colorimetric Differences
Rubine & rhodamine – Spectral reflectance in the blue region of SPC – Hue angle of the a* b* diagram
0
10
20
30
40
50
60
70
80
90
100
400 450 500 550 600 650 700
Wavelength (nm)
RubineRhodamine
% R
efle
ctan
ce
b*
-80
-60
-40
-20
0
20
40
60
80
-80 -60 -40 -20 0 20 40 60 80
a*•
•Rubine
Rhodamine
(Yellowish)!
(Bluish)!
47
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Colorimetric Specifications
ISO 2846—Standardized printing inks for offset lithography – C, M, Y, K – A single set of color coordinates could adequately represent
standard inks around the world. - Endorsed by ink associations from Europe, America, and Japan
48
Colorimetry and Its Application 25
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ISO 2846-1 (2006)
Sample preparation – Should be made on the reference substrate
- APCO II/II – The nominal ink film thickness for web heat-set ink is 1 mm.
- 0.7-1.3 mm for cyan, magenta, and yellow - 0.9-1.3 mm for black
49
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ISO 2846-1 (2006)
Specification for color and transparency of printing inks – Sheet-fed and heat-set web offset
Colorimetric conditions – D50 illuminant / 2o observer
50
Colorimetry and Its Application 26
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ISO 2846-1 (2006)
Example of conformance – Ink 1
Example of non-conformance – Ink 2—Deviation of ink color – Ink 3 —correct in ink color, not in
pigment concentration
1.0 1.50.5
2
4
6
8
10
0
∆E
Ink film thickness (µm)
1
2
3
tolerancerange
51
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Process Characterization
Color gamut comparison – Monitor color gamut – Printer color gamut
Color variations – Spatial uniformity within the sheet – Temporal consistency from sheet-to-sheet – XYZ-based TVI assessment
52
Colorimetry and Its Application 27
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Monitor Color gamut
Ambient lighting influences monitor color gamut.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8x
y G
C
B
M
R
Y
W
CIE spectrum locus
Dark
Light Dim
700600
575
550
525
500
475
450400
53
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Monitor Color Gamut
Ambient lighting also influences lightness range of the monitor. – High ambient lighting
- Adds flare in the black point - Reduces lightness range
0 10 20 30 40 50 60 70 80 90 100Y
DarkDim
LightHard copy
(black) (white)
Hard copy has brighter white point!
54
Colorimetry and Its Application 28
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Printer Color Gamut
Chromaticity / a*b* diagram can be deceiving. – Expressed in two dimensions without lightness
y
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0x
G
Y
R
M
B
C
CIE Spectrum Locus
700600
575
550
525
500
475
450400
Increaseddensity
Decreaseddensity
CIELAB a*b* -100
-50
0
50
100
-100 -50 0 50 100
a*
b*
Increased density
decreased density
55
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Printer Color Gamut Slice
Chromaticity at constant lightness plane requires special test targets.
-100
-80
-60
-40
-20
0
20
40
60
80
100
-100 -80 -60 -40 -20 0 20 40 60 80 100a*
56
Colorimetry and Its Application 29
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Color Variation Rules
All imaging processes have color variations. – Some processes have more variations than other processes.
Sources of variability – Uniformity within the sheet – Sheet-to-sheet – Run-to-run
Assignable variations can be corrected for; random variations cannot.
57
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Uniformity within the Sheet
Spot color by flexo (30 measurements across) Sample - Average Sample - Average
Location # L * a * b * ∆L* ∆a* ∆b* ∆ E Location # L * a * b * ∆L* ∆a* ∆b* ∆ E1 31.5 11.7 7.9 0.2 -0.1 -0.2 0.3 1 52.4 61.8 39.0 0.2 -0.9 -1.1 1.42 31.7 11.8 8.0 0.3 0.0 -0.1 0.4 2 52.3 62.2 39.6 0.0 -0.5 -0.6 0.83 31.5 11.8 8.1 0.2 0.0 0.0 0.2 3 52.3 62.1 39.6 0.0 -0.6 -0.6 0.84 31.6 11.7 8.0 0.3 -0.2 0.0 0.3 4 52.2 62.6 40.2 0.0 -0.1 0.0 0.15 31.6 11.8 8.0 0.3 0.0 0.0 0.3 5 51.8 62.7 40.4 -0.5 0.0 0.2 0.56 31.6 11.9 8.0 0.2 0.0 0.0 0.3 6 52.1 63.1 40.7 -0.1 0.4 0.5 0.77 30.8 11.8 8.0 -0.5 -0.1 -0.1 0.6 7 52.1 63.2 40.6 -0.2 0.5 0.5 0.78 30.9 11.8 8.2 -0.4 0.0 0.1 0.4 8 52.5 62.9 40.1 0.2 0.2 -0.1 0.39 31.1 12.0 8.1 -0.2 0.1 0.0 0.2 9 52.8 63.1 40.4 0.5 0.5 0.2 0.7
10 31.2 12.1 8.1 -0.1 0.3 0.0 0.3 10 52.1 61.5 39.1 -0.2 -1.2 -1.1 1.611 31.7 12.3 8.2 0.4 0.5 0.2 0.6 11 52.2 63.0 40.6 0.0 0.3 0.4 0.512 31.5 11.9 8.0 0.2 0.0 0.0 0.2 12 52.8 64.0 41.1 0.5 1.4 1.0 1.713 31.4 11.8 8.0 0.1 -0.1 0.0 0.1 13 51.8 62.6 39.9 -0.4 -0.1 -0.2 0.514 31.6 11.9 8.1 0.3 0.0 0.0 0.3 14 52.2 62.6 40.0 -0.1 0.0 -0.2 0.215 31.0 11.6 8.0 -0.4 -0.2 0.0 0.4 15 52.1 62.5 39.7 -0.2 -0.1 -0.4 0.516 31.4 11.7 8.0 0.0 -0.1 -0.1 0.1 16 52.6 62.7 40.0 0.3 0.0 -0.1 0.317 31.1 11.7 8.0 -0.3 -0.1 0.0 0.3 17 52.3 62.9 40.2 0.1 0.2 0.1 0.218 31.3 11.9 8.0 -0.1 0.0 0.0 0.1 18 52.4 62.8 40.0 0.1 0.1 -0.1 0.219 31.3 11.9 8.1 0.0 0.1 0.1 0.1 19 52.3 62.2 39.7 0.0 -0.5 -0.5 0.720 31.4 12.2 8.3 0.1 0.3 0.3 0.4 20 51.8 61.9 39.8 -0.5 -0.8 -0.4 1.021 31.9 12.3 8.3 0.6 0.4 0.3 0.8 21 52.3 62.8 40.2 0.1 0.2 0.0 0.222 31.4 12.0 8.2 0.1 0.2 0.2 0.3 22 52.2 62.8 40.2 0.0 0.1 0.0 0.123 30.7 11.8 7.8 -0.6 0.0 -0.2 0.6 23 52.0 62.5 40.3 -0.2 -0.2 0.1 0.324 31.1 11.7 8.0 -0.2 -0.1 0.0 0.2 24 52.0 62.3 40.3 -0.2 -0.4 0.1 0.525 31.1 11.8 8.1 -0.3 0.0 0.0 0.3 25 52.2 62.6 40.2 -0.1 -0.1 0.0 0.126 31.1 11.8 8.0 -0.3 -0.1 0.0 0.3 26 52.5 63.5 40.9 0.2 0.8 0.8 1.127 30.8 11.6 7.9 -0.5 -0.3 -0.1 0.6 27 52.4 63.0 40.6 0.2 0.3 0.4 0.628 31.4 11.8 8.0 0.1 -0.1 0.0 0.1 28 52.6 63.0 40.5 0.3 0.4 0.3 0.629 31.3 11.7 8.0 -0.1 -0.2 -0.1 0.2 29 52.9 63.5 40.9 0.6 0.8 0.8 1.330 31.9 11.7 7.9 0.6 -0.2 -0.1 0.6 30 52.0 62.1 39.8 -0.2 -0.6 -0.3 0.7
A v e r a g e 31 .3 11 .8 8 . 0 ∆E Ave. 0 . 3 A v e r a g e 52 .3 62 .7 40 .1 ∆E Ave. 0 . 6∆E Max. 0.8 ∆E Max. 1.7∆E Min. 0.1 ∆E Min. 0.1∆E Range 0.7 ∆E Range 1.7
52_B rown 75_Red
58
Colorimetry and Its Application 30
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Consistency from Sheet-to-sheet
Spot color by flexo (30 consecutive sheets) Sample - Average Sample - Average
Sample # L * a * b * ∆L* ∆a* ∆b* ∆ E Sample # L * a * b * ∆L* ∆a* ∆b* ∆ E1 31.6 11.8 8.2 0.1 0.0 0.0 0.1 1 52.7 63.2 40.5 0.3 0.2 0.0 0.42 31.1 11.4 8.0 -0.3 -0.4 -0.3 0.6 2 52.4 63.5 40.9 -0.1 0.5 0.5 0.73 31.6 11.8 8.3 0.1 0.0 0.1 0.1 3 52.3 63.3 41.2 -0.1 0.3 0.7 0.84 31.8 11.8 8.3 0.3 0.0 0.1 0.3 4 52.1 62.6 40.5 -0.4 -0.3 0.0 0.55 31.5 11.7 8.2 0.1 -0.1 -0.1 0.1 5 52.4 63.2 40.7 0.0 0.2 0.3 0.46 31.0 11.5 8.1 -0.4 -0.3 -0.2 0.5 6 52.3 62.4 40.2 -0.1 -0.5 -0.3 0.67 31.5 12.0 8.3 0.0 0.2 0.1 0.2 7 52.5 62.9 40.4 0.1 -0.1 -0.1 0.18 31.4 11.8 8.2 -0.1 0.0 0.0 0.1 8 52.7 63.5 40.7 0.3 0.5 0.2 0.69 31.2 11.5 8.1 -0.2 -0.3 -0.2 0.4 9 52.5 62.7 40.3 0.1 -0.2 -0.2 0.3
10 31.0 11.9 8.3 -0.5 0.1 0.1 0.5 10 52.6 63.0 40.5 0.2 0.0 0.0 0.211 32.0 12.1 8.5 0.5 0.3 0.2 0.6 11 52.4 63.4 41.0 0.0 0.5 0.5 0.712 31.5 12.1 8.4 0.1 0.3 0.1 0.3 12 52.4 62.6 40.1 -0.1 -0.4 -0.4 0.613 31.8 11.7 8.2 0.4 -0.1 0.0 0.4 13 52.0 62.4 40.0 -0.4 -0.5 -0.5 0.814 31.5 11.7 8.2 0.0 -0.1 -0.1 0.1 14 52.9 63.2 40.7 0.4 0.3 0.2 0.515 31.6 11.7 8.2 0.1 -0.1 -0.1 0.2 15 52.6 62.7 40.0 0.1 -0.3 -0.5 0.616 31.4 11.8 8.2 -0.1 0.0 0.0 0.1 16 52.8 63.4 40.5 0.4 0.4 0.1 0.617 31.3 11.9 8.4 -0.2 0.1 0.1 0.3 17 52.4 62.5 40.1 -0.1 -0.5 -0.4 0.618 31.4 11.8 8.2 -0.1 0.0 0.0 0.1 18 52.3 62.3 39.9 -0.1 -0.7 -0.6 0.919 31.7 12.1 8.3 0.2 0.2 0.1 0.3 19 52.4 62.7 40.1 0.0 -0.2 -0.4 0.520 31.4 11.9 8.3 0.0 0.1 0.1 0.1 20 52.4 62.6 40.4 0.0 -0.4 -0.1 0.421 31.4 11.8 8.3 -0.1 0.0 0.0 0.1 21 52.4 63.1 40.7 -0.1 0.1 0.2 0.322 31.9 12.1 8.4 0.4 0.2 0.1 0.5 22 52.3 62.7 40.2 -0.2 -0.2 -0.2 0.423 31.6 11.9 8.3 0.1 0.1 0.0 0.2 23 52.5 63.7 41.1 0.0 0.8 0.6 1.024 31.5 11.6 8.1 0.0 -0.2 -0.1 0.2 24 52.0 62.5 40.3 -0.4 -0.5 -0.2 0.625 31.3 11.7 8.1 -0.2 -0.1 -0.1 0.2 25 52.8 63.2 40.6 0.4 0.2 0.1 0.526 31.4 11.8 8.2 0.0 0.0 0.0 0.0 26 52.7 62.9 40.1 0.2 0.0 -0.4 0.527 31.6 11.8 8.1 0.1 0.0 -0.1 0.2 27 52.5 63.6 41.1 0.0 0.6 0.6 0.928 31.5 12.0 8.4 0.1 0.2 0.1 0.2 28 52.6 63.3 40.9 0.1 0.3 0.4 0.529 31.2 11.6 8.2 -0.3 -0.2 -0.1 0.4 29 52.4 62.6 40.2 0.0 -0.3 -0.3 0.430 31.3 11.9 8.4 -0.1 0.1 0.1 0.2 30 52.1 62.8 40.4 -0.3 -0.2 -0.1 0.4
A v e r a g e 31 .5 11 .8 8 . 2 ∆E Ave. 0 . 3 A v e r a g e 52 .4 62 .9 40 .5 ∆E Ave. 0 . 5(Production ∆E Max. 0.6 (Production ∆E Max. 1.0
center) ∆E Min. 0.0 center) ∆E Min. 0.1∆E Range 0.6 ∆E Range 0.9
52_B rown 75_Red
59
Copyright 2015 RIT – May not be reproduced without permission
XYZ-based TVI (ISO/TS 10128)
Magenta and black
Yellow
Cyan
€
TVI =100 Yp −YtYp −Ys
#
$ %
&
' ( − InputTV
€
TVI =100 Zp − ZtZp − Zs
#
$ %
&
' ( − InputTV
€
TVI =100 Xp − 0.55Zp( ) − Xt − 0.55Zt( )Xp − 0.55Zp( ) − Xs − 0.55Zs( )
#
$ % %
&
' ( ( − InputTV
Subscripts p: paper t: tint s: solid
60
Colorimetry and Its Application 31
Copyright 2015 RIT – May not be reproduced without permission
Color Matching
Spot color printing vs. CMYK printing – Avoid out-of-gamut color – Small ∆E matters
Pantone swatchbook is printed by dry offset using special formulated inks. Pantone-to-digital printing uses a RIP-based look-up table.
61
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Pictorial Color Image
Pleasingness of the reproduction matters. – Minimum ∆E is not important
- Particularly when ∆E is due to gamut clipping
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Colorimetry and Its Application 32
Copyright 2015 RIT – May not be reproduced without permission
Color Image Reproduction
Color Research & Appl. (Pearson, 1986) – Large ∆Es exist between the original and a very acceptable
photographic print - Tone reproduction and gamut compression are key factors for
pleasing reproduction
All patches Std. Observer Geometry color temp.statistics in Macbeth from 1931 to 0/45 to difference
colorchecker 1964 sphere by 400oKAverage 15.9 1.4 3.2 3.1Std. dev. 6.8 1.6 3.3 2.3Min. 4.4 0 0.2 0.5Max. 31.7 4.7 12.3 8.4Range 27.3 4.7 12.1 7.9
63
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Summary Densitometer Spectro-colorimeter
Unit density XYZ, Yxy, CIELABDifference none ∆E(Single number)
Spectral match to peak absorp- match the 1931 CIEresponse tion of process inks standard observerGeometry 0/45 0/45, integrating Color anomalous color-normalperception trichromat observerDark shade good okaydiscrimin.Light shade poor gooddiscrimin.Standardization ANSI status T CIEApplications process control for color specification
CMYK printing only process controlquality assurance
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Colorimetry and Its Application 33
Copyright 2015 RIT – May not be reproduced without permission
Summary
Colorimetry has multiple uses in graphic arts imaging practices. – Ink specifications and standardization – Process characterization and standardization – Spot color matching
Colorimetry cannot judge pleasingness of pictorial color images. – Only the human color perception can
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