perceptual color space - אוניברסיטת חיפה
TRANSCRIPT
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Perceptual Color Space
Lecture 5
CIELAB Color Space
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Color Based Image Retrieval
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Color Based Image Retrieval
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Color Based Image Retrieval
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0.2
0.4
0.6
0.8
0
y
0.2 0.4 0.60
Non- Perceptual Color Space
Equal Euclidean distances are nor perceivedas equally distant perceptually.
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Luminance vs BrightnessY vs V : Luminance (intensity) vs Brightness (Lightness)
Lum
inan
ce
∆I1
∆I2I2
I1
I1 < I2, ∆I1 = ∆I2
Equal intensity steps:
Equal brightness steps:
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Weber’s Law
In general, ∆I needed for just noticable difference (JND) over background I was found to satisfy:
∆II
= constant
(I is intensity, ∆I is change in intensity)
Weber’s Law:
Perceived Brightness = log (I)
Intensity
Per
ceiv
ed B
right
ness
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Shepard (1962) – judgments of similarity of Munsellchips associated with monochromatic spectra.
Perceptual Color Distances
Figure From www.handprint.com/HP/WCL/color2.html
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Munsell lines of constant Hue and Chroma.
x
y
0 0.1 0.2 0.3 0.4 0.5 0.60
0.1
0.2
0.3
0.4
0.5
Value =1/
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MacAdam - JND (Just Noticable difference)
test non-match
0.2
0.4
0.6
0.8
0
y
0.2 0.4 0.60
+ -
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MacAdam Ellipses of JND (Just Noticable difference)
0.2
0.4
0.6
0.8
0
y
0.2 0.4 0.60 x
(Ellipses scaled by 10)
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The transformation from XYZ space to perceptual space is Non Linear:
Linear approximation defined by CIE (1960):CIE Uniform Chromaticity Scale (UCS) :
U = X 23
V = Y
W = -X + 3Y + Z2
0.66 0 00 1 0-0.5 1.5 0.5
XYZ
UVW
=
CIE- UVW Coordinates
u = 4x-2x + 12y + 3
v = 6y-2x + 12y + 3
CIE-uv Chromaticity Coordinates:
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Munsell lines of constant hue and chromaplotted in CIE-uv coordinates:
u
v
0 0.1 0.2 0.3 0.4 0.5 0.60
0.1
0.2
0.3
0.4
Value =1/
See also Online demo at:http://www.brucelindbloom.com/MunsellCalculator.html
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CIE- L*u*v* CoordinatesCIE- L*u*v* Coordinates = modified UCS system
u* = 13 L*(u’-u0’)
v* = 13 L*(1.5v’-v0’)
{L* = 116(Y/Y0)1/3 - 16 for Y/Y0903(Y/Y0) otherwise
u0 v0 Y0 = coordinates of reference white
(1976)
u‘ = uv‘ = 1.5 v
> 0.01
A color model for which, a unit change inluminance and chrominance are uniformly perceptible
u = 4x-2x + 12y + 3
v = 6y-2x + 12y + 3
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b* = 200 [ (X/X0) 1/3 - (Z/Z0)1/3]
CIE- L*a*b* Coordinates
a* = 500 [ (X/X0) 1/3 - (Y/Y0)1/3]
X0 Y0 Z0 = coordinates of reference white
L* = 116(Y/Y0)1/3 - 16 for Y/Y0903(Y/Y0) otherwise
> 0.01
L – Luminance
a – ranges from green to red
b – ranges from blue to yellow
{*
L – ranges from 0..100 with 50 average gray and 100 reference white.a,b – unbounded but usually between -120..+120
Colors are relative to a reference white point.
(1976)
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LAB Color Solid
Hab = arctan(b*/a*)
Cab = ((a*)2+(b*)2)1/2
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Munsell lines of constant hue and chromaplotted in CIE- L*u*v* Coordinates:
u*-150 -100 -50 0 50 100 150
-150
Value =5/
200
100
50
0
-50
-100
v*
MacAdam Ellipses of JND plotted in CIE- L*u*v* Coordinates:
u*-150 -100 -50 0 50 100 150 200
-150
100
50
0
-50
-100
v*
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http://www.brucelindbloom.com/index.html?ColorCalcHelp.html
Color Coordinate Calculator:
http://www.brucelindbloom.com/index.html?Equations.html
Color Space Conversions
Color Conversions
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Color Based Image Retrieval
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Measuring Color Differences
∆e 2 = ∆L*2 + ∆a* 2 + ∆b* 2
∆e2 = ∆L*2 + ∆u* 2 + ∆v* 2
∆e = 3 visually indistiguishable∆e = 5 acceptable error (most printers)∆e = 10 bad∆e = 15 unacceptable
error for ∆I1 : ∆e = 37.36error for ∆I2 : ∆e = 4.64
Lum
inan
ce
∆I1
∆I2I2
I1
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Measuring Color Differences
CIELAB – assumes uniform patches of at least 2degvisual angle on uniform background.
BUT – color appearance depends on spatial patterns.
?
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S-CIELAB
S-CIELAB adds a spatial pre-processing step to thestandard CIELAB Delta-E metric to account for thespatial-color sensitivity of the human eye.
S-CIELAB – a spatial extension to CIELAB.
Zhang & Wandell (1997).
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S-CIELAB- ExampleOriginal
Jpeg Compressed (factor = 75)
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S-CIELAB
Luminance
Red-Green
Blue-Yellow
CIELAB - ∆E
S-CIELAB - ∆E
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Perceptual Color SpacesCIELAB – assumes uniform patches of at least 2deg
visual angle on uniform background. S-CIELAB – takes spatial pattern into account.
BUT – color appearance depends on luminance adaptation, chromatic contrastand chromatic assimilation.
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Color Appearance
Adelson
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Adelson
Color Appearance
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Perceptual Color Spaces
Color appearance also depends on surround contrast –for example different media.
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CIECAM02
2002 Perceptual space – new CIE standard.
(R. Hunt, Y. Nayatani, M. Fairchild, N. Moroney )
Figure from http://www.handprint.com/HP/WCL/color7.html#CIECAM
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CIECAM02
Figure from http://en.wikipedia.org/wiki/CIECAM02
Background
Surround
Stimulus
Proximal Field
Stimulus - measured in CIE XYZ (2° standard). proximal field - extends out another 2°. background - extends out to 10°, in which relative
luminance (Yb) is measured. If background colorequals the proximal field, it is considered adjacentto the stimulus.
surround - considered to be the entire room.
adapting field = proximal field + background + surround.
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CIE – Standard Color SpacesCIE 1931 XYZ CIELUV CIELAB CIEUVW
RGB color SpacesRGB sRGBAdobe RGB Adobe Wide Gamut RGB
Luminance plus chrominanceYIQ, YUV, YDbDrYPbPr, YCbCrxvYCC
Hue and saturationHSV HSL
Subtractive / Multiplicative color spacesCMYK
Commercial color spacesMunsell color systemNatural Color System (NCS) Pantone Matching System (PMS)
Summary Color Spaces
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Color Perception - CaveatsColor Memory
migration towards extreme:bright colors are remembered as brighterdark colors are remembered as darker
migration towards standard:off-colors are remembered more saturated
migration towards characteristic hues:apples are remembered more “red”bananas more “yellow” than they aregrass more “green” than it is.
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Color Memory - Experiment
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Color Focals
Across cultures:Boundary between one color term and another is in pooragreement (same orange -> red in one culture but -> yellow (or "tan", or "warm", or "light") in another.
However, focal color or best exemplar for a color, is quite consistent.
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Color Naming
Color Names:western world - 11 basic color namessome primitive cultures: light, darkothers: light, dark, redLakuti tribe: same name for blue and green.
But: limitation of color names does not affect ability to match, discriminate or reproducecolor (Berlin & Kay ‘69, Bornstein ‘73,’75)
Color & feeling:yellow, red - “warm” colorsblue, brown, black - “cool” colors
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Berlin & Kay
Evolutionary Trajectories of Color Names
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Frequency of Color Names in English Text
black 0.024%white 0.023%red 0.015%dark 0.012%blue 0.0106%green 0.0105%light 0.0099%bright 0.0072%gray 0.0056%brown 0.0050%yellow 0.0048%pale 0.0041%pink 0.0034%dull 0.0021%orange 0.0017%silver 0.0014%purple 0.0013%gold 0.0013%
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Wattenberg's Version of the Color Name Cloud
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Look at the chart and say the not the word.
Left - Right ConflictYour right brain tries to say the color butYour left brain insists on reading the word.
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Color & Culture
Color symbolism:white - wedding in western world
mourning & death in Chinese culturered - youth, party, bold in western world
wedding in Chinese cultureSaturated colors – preferred in Japan
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Color & Health
Color & mood:yellow, red - “warm” colorsblue, brown, black - “cool” colors
http://geocities.com/iiii_velvet_underground_iiii/COLOURTHERAPY.html
http://www.holisticonline.com/Color/color_diseases_and_treatment_N.htm
Color Therapy:Nausea – Treat with BlueNervous Disorders - Treat with green.Kidney stones – Treat with Orange
Autistic children –found that blue-green scarves– relaxes/quiets red-black-yellow irritating!
Eating in blue makes you eat less as it relaxes and slows you down.
Eating in orange makes you eat faster and more .
The color coral (orange-pink) had been shown toreduce stress and violence.
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Happy - YellowPure - WhiteGood Luck - GreenGood-tasting - Red (tomato)Dignity - PurpleHigh Technology - SilverSexiness - Red (tomato)Mourning - BlackExpensive - GoldInexpensive - BrownPowerful - Red (tomato)Dependable - BlueHigh Quality - BlackNausea - GreenDeity - WhiteBad Luck - BlackFavorite Color - BlueLeast Favorite Color - Orange
Global Color Survey
Since 1997, over 30,000 people from all over the globe took the survey. Results:
For more information click here.http://www.colorcom.com/research.html
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"Enhancement of blue"Blue circles appear to be enhanced in saturation
when seen in the central vision.
Copyright A.Kitaoka 2003
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"Flowers"Red appears to be magenta or orange.
This is kind of von Bezold's chromatic assimilation.
Copyright A.Kitaoka 2003
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"Green and blue spirals“There appear to be spirals of light green or light blue. Actually, they are identical (r = 0, g = 255, b = 150). Basic illusion proposed by Monnier and Shevell (2003).
Copyright A.Kitaoka 2003
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Yuval Barkan + Hedva Spitzer 2009
AfterImage Fill In
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white slide for after Image