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G. Sawitzki: Colour August 20, 2012 1
Colour
Gunther [email protected]
www.statlab.uni-heidelberg.de
May 10, 2012revised August 20, 2012
G. Sawitzki: Colour August 20, 2012 2
FundamentalsPhysicsPhysiologyMetamers
RGB WorldColor Matching Data
Reproducible Colour
Coordinates
Background
G. Sawitzki: Colour August 20, 2012 3
Basics
G. Sawitzki: Colour August 20, 2012 4
Colours
G. Sawitzki: Colour August 20, 2012 5
Colours do not exist.
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Colour is produced by visual perception.
G. Sawitzki: Colour August 20, 2012 7
The physicists view. Prisma. Electromagnetic Spectrum.
G. Sawitzki: Colour August 20, 2012 8
Physiology. Receptors with frequency-dependent characteristics.
G. Sawitzki: Colour August 20, 2012 9
Metamers.Different spectral distributions may yield equivalent colour
impression.
G. Sawitzki: Colour August 20, 2012 10
The RGB world.
G. Sawitzki: Colour August 20, 2012 11
G. Sawitzki: Colour August 20, 2012 12
Color Matching Data
Short description
Colour matching functions of20 individual observers.
The observers are trying tomatch a reference light ofgiven frequency by mixingred r , green g and blue blight with adjustable intensity.Data Source:
Gunter Wyszecki & W.S. Stiles (1982) Color Science, 2nd ed. NY: Wiley , pp 817-822after Stiles and Burch 1959.
G. Sawitzki: Colour August 20, 2012 13
Color Matching Data
Short description
Colour matching functions of20 individual observers.
The observers are trying tomatch a reference light ofgiven frequency by mixingred r , green g and blue blight with adjustable intensity.
n = 20 cases=observersp = 1 regressors ()
with 34 stepsq = 3 response variables r , g , b
dim observation space: 3or
dim observation space: 3 34
G. Sawitzki: Colour August 20, 2012 14
Color Matching Data
Green light intensity by
Green intensity for observerMCB(14) at =620nm:5.881E-1.
This gives an extreme outlier.
Presumably the correct valuewas 5.881E-2, giving thelower plot in this display.
G. Sawitzki: Colour August 20, 2012 15
Color Matching Data
Intensity componentsr , g , b components in the toprows, together with asmoothed fit.
middle row: residuals.
The outlier has been removedin this plot.
The colour code in this plot isnot calibrated and should beused for rough orientationonly.
G. Sawitzki: Colour August 20, 2012 16
Color Matching Data
Intensity components: model
Color matching functions inRGB space for 20 individualobservers.
G. Sawitzki: Colour August 20, 2012 17
Color Matching Data
Intensity components: modelColor matching functions inRGB space for 20 individualobservers.
Model function:One dimensional datastructure in 3-space.
G. Sawitzki: Colour August 20, 2012 18
Color Matching Data
Dont forget the residuals !
G. Sawitzki: Colour August 20, 2012 19
Color Matching Data
Intensity components: residuals
Color matching functions inRGB space for 20 individualobservers.
Residuals in 3-space.
Background Information
G. Sawitzki: Colour August 20, 2012 20
Color Matching Data
Intensity components: residualsColor matching functions inRGB space for 20 individualobservers.
Residuals in 3-space:
2 dimensional planar structure(rotational symmetry?)
1 dimensional rod, orthogonalto planar structure.
Background Information
G. Sawitzki: Colour August 20, 2012 21
Color Matching Data
What did we use ?
I colour encoding of regressor values
I linking
I projection
I rotation
G. Sawitzki: Colour August 20, 2012 22
Color Matching Data
What did we use ?
I colour encoding of regressor values
I linking
I projection
I rotation
G. Sawitzki: Colour August 20, 2012 23
Color Matching Data
What did we use ?
I colour encoding of regressor values
I linking
I projection
I rotation
G. Sawitzki: Colour August 20, 2012 24
Color Matching Data
What did we use ?
I colour encoding of regressor values
I linking
I projection
I rotation
back to intro
G. Sawitzki: Colour August 20, 2012 25
Color Matching Data Background Information
Spectrum
For a first approach, colourperception is generated bylight.
Light may be considered anelectromagnetic wave withintensities in the visible rangeof the electromagneticspectrum.
G. Sawitzki: Colour August 20, 2012 26
Color Matching DataBackground Information
Primary Perception
The primary perception ofcoulour in the eye is by conecells.
Cone cells come in threekinds, sensitive to differentparts of the spectrum.
Fromhttp:
//www.d.umn.edu/~mharvey/th1501color.html
http://www.d.umn.edu/~mharvey/th1501color.htmlhttp://www.d.umn.edu/~mharvey/th1501color.html
G. Sawitzki: Colour August 20, 2012 27
Color Matching DataBackground Information
Secondary Perception (Theory)
Colour perception reduces theinformation from the cones tothree information channels,the tristimulus value.
The next step separatesinformation aboutluminescence from colordifferences.
From D. Travis: Effective Color Display
G. Sawitzki: Colour August 20, 2012 28
Color Matching DataBackground Information
MetamersDifferent spectral distributions may give the same perceivedcoulours. By mixing only few colours, you can generate theimpression to cover a spectrum. Colours thus matchedperceptually are called metamers.You can experiment with metamers with software downloadable
I from Brown universityhttp://www.cs.brown.edu/exploratories/freeSoftware/repository/edu/
brown/cs/exploratories/applets/spectrum/metamers_guide.html
I fromhttp://www.colourware.co.uk/www.colourware.co.uk/cpfaq/q1-1.htm
http://www.cs.brown.edu/exploratories/freeSoftware/repository/edu/brown/cs/exploratories/applets/spectrum/metamers_guide.htmlhttp://www.cs.brown.edu/exploratories/freeSoftware/repository/edu/brown/cs/exploratories/applets/spectrum/metamers_guide.htmlhttp://www.colourware.co.uk/www.colourware.co.uk/cpfaq/q1-1.htm
G. Sawitzki: Colour August 20, 2012 29
Color Matching DataBackground Information
See also:I Colour Theory
http://www.luminous-landscape.com/tutorials/colour_theory.shtml
I Colour Physics http://www.colourware.co.uk/cpfaq.htm
I wikipedia: color vision http://en.wikipedia.org/wiki/Color_vision
back to intro
http://www.luminous-landscape.com/tutorials/colour_theory.shtmlhttp://www.colourware.co.uk/cpfaq.htmhttp://en.wikipedia.org/wiki/Color_vision
G. Sawitzki: Colour August 20, 2012 30
Spectrum in RGB space
G. Sawitzki: Colour August 20, 2012 31
Linear interpolation in RGB spaceSingle colour gradientsTwo colour interpolationParabola
G. Sawitzki: Colour August 20, 2012 32
Alternate coordinate system: Total intensity.
Z = R + G + B
r = R/Z g = g/Z
Use polar coordinates in r , g space.
G. Sawitzki: Colour August 20, 2012 33
G. Sawitzki: Colour August 20, 2012 34
G. Sawitzki: Colour August 20, 2012 35
G. Sawitzki: Colour August 20, 2012 36
G. Sawitzki: Colour August 20, 2012 37
G. Sawitzki: Colour August 20, 2012 38
Printing colours are complementary to screen colours.
G. Sawitzki: Colour August 20, 2012 39
Colour matching using profiles
G. Sawitzki: Colour August 20, 2012 40
The RGB world.
G. Sawitzki: Colour August 20, 2012 41
The RGB world.
G. Sawitzki: Colour August 20, 2012 42
But . . . there is a world outside the cube.
G. Sawitzki: Colour August 20, 2012 43
Colour circle: Itten (1961)
G. Sawitzki: Colour August 20, 2012 44
Goethes and Newtons colour circle.
G. Sawitzki: Colour August 20, 2012 45
HSV colour coordinates
G. Sawitzki: Colour August 20, 2012 46
Lab colour coordinates
G. Sawitzki: Colour August 20, 2012 47
sRGB in Lab coordinates.
G. Sawitzki: Colour August 20, 2012 48
G. Sawitzki: Colour August 20, 2012 49
G. Sawitzki: Colour August 20, 2012 50
G. Sawitzki: Colour August 20, 2012 51
G. Sawitzki: Colour August 20, 2012 52
bump
G. Sawitzki: Colour August 20, 2012 53
G. Sawitzki: Colour August 20, 2012 54
G. Sawitzki: Colour August 20, 2012 55
G. Sawitzki: Colour August 20, 2012 56
References I
http://www.cslkamloops.org/IMG/rainbow_smoke.png
http://1.bp.blogspot.com/-kqZvjxE7CDU/T1DkM2IIukI/AAAAAAAABD0/i_QljqtvOD0/s1600/rainbow.jpg
http://www.physik.uni-bayreuth.de/physikstudium/images/prisma.jpg
http://www.webexhibits.org/colorart/i/cone-spectral-sensitivitie.jpg
http://en.wikipedia.org/wiki/File:RGB_illumination.jpg
http://www.cslkamloops.org/IMG/rainbow_smoke.pnghttp://1.bp.blogspot.com/-kqZvjxE7CDU/T1DkM2IIukI/AAAAAAAABD0/i_QljqtvOD0/s1600/rainbow.jpghttp://www.physik.u