Colour - StatLab · PDF fileG. Sawitzki: Colour August 20, 2012 1 Colour ... Colour circle: Itten (1961) G. Sawitzki: Colour August 20, 2012 44 Goethe’s and Newton’s colour circle

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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

    [email protected]

  • 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

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    Colours do not exist.

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    Colour is produced by visual perception.

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    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.

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  • 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.

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    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

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  • 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

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  • 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