physics of colour perception
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Science of Colour Perception
Siddharth KasthuriranganInstitute of Chemical Technology
R. Ruia College, Matunga
1st
December, 2010.
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What is Colour?
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What is Colour?
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What is Colour?
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What is Colour?
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What is Colour?
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What is Colour?
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Importance of Colour
The most important of
our five sensory organs
Colours can affect our
thoughts, emotions andfeelings
Colour specification is
highly perception-based
Consumer-oriented
markets are being
increasingly driven by
colour Colour can be correlated
to the chemical purity of
a substance
Need to Understand Colour Better
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Colour as a Physical Quantity
Measurement of colour, as one would measure
any physical quantity
Repeatability and reproducibility of results
Colour vision or perception is an inherently
psychological and physiological phenomenon
Many challenges unique to the subject ofcolour science for which unique solutions have
to be found
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Observers Situation in Colour Science
OBJECT
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What is Colour?
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Is Colour Wavelength?
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Sir Isaac Newton
Ifat any time I speak of Lightand Rays as coloured or enduedwith Colours, I would beunderstood to speak not
philosophically and properly,
but grossly, and according tosuch Conceptions as vulgarPeople would be apt to frame.For the Rays to speak properlyare not coloured. In them there
is nothing else than a certainPower and Disposition to stir upa Sensation of this or thatColour.
Ifat any time I speak of Lightand Rays as coloured or enduedwith Colours, I would beunderstood to speak not
philosophically and properly,
but grossly, and according tosuch Conceptions as vulgarPeople would be apt to frame.For the Rays to speak properlyare not coloured. In them there
is nothing else than a certainPower and Disposition to stir upa Sensation of this or thatColour.
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Newtons Colour Wheel
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First Colour Photograph
J. C. Maxwell, 1861
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Combining Colours
R+B = Magenta
R+G = Yellow
B+G = Cyan
R+B+G = White
WB = Yellow
WG = Magenta
WR = Cyan
WRBG = Black
R+B = Magenta
R+G = Yellow
B+G = Cyan
R+B+G = White
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Quantifying Colour
Mass
Length
Time
Colour
?
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Combining Colours
[ ] [ ] [ ] [ ]P P R R B B G G
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Colours obtained by Additive Mixing
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Imaginary Primaries
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Tristimulus Values
[ ] [ ] [ ] [ ]P P X X Y Y Z Z
700
400
700
400
700
400
X x R E
Y y R E
Z z R E
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Three Dimensions of Colour
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CIE L*a*b*1
3
0
1 13 3
0 0
1 13 3
0 0
* 116 16
* 500
* 200
YL
Y
X YaX Y
Y Zb Y Z
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The Observers Triplet Revisited
OBJECT
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Light Sources
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Properties of Objects
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The Observer
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Colour Measurement
SOURCE OBSERVEROBJECT
L* = ###.##
a* = ###.##
b* = ###.##
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Colour Measurement
SOURCE OBSERVEROBJECT
L* = ###.##
a* = ###.##
b* = ###.##
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Metamerism
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Where do we stand?
Colour is perceived as a three-dimensionalphysicalquantity and can be measuredusing reflectances ofsurfaces under specified illumination and dependingon detector characteristics
The colour industry is thriving today because we havea good working knowledge of the science behindcolour appearance
There are open problems in colour contrast andcolour perception mechanisms which areinterdisciplinary in nature combining physics,
biology, chemistry, neuroscience and theoreticalcomputer science
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Colour Contrast
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Koffkas Ring
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Negative After-image
CYAN MAGENTA YELLOW
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Watch This
www.michaelbach.de/ot/col_lilacChaser/index.html
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Non-adjacent Surround
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Adelsons Checkerboard
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Colour and Human Psychology
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Colour Harmony
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Complementary Colour Scheme
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Analogous Colour Scheme
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Triadic color scheme A triadic color scheme uses colors that are evenly spaced around the color
wheel.
Triadic color schemes tend to be quite vibrant, even if you use pale or
unsaturated versions of your hues. To use a triadic harmony successfully, the colors should be carefully
balanced - let one color dominate and use the two others for accent.
Triadic Colour Scheme
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Split Complementary Scheme
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Who needs Colour Science?
Industry
Paints
Cosmetics
Textiles and Dyes Packaging
Interior Design
TVs and Displays
Oils and Foods
Pharmaceuticals
Academics
Unique specification ofcolour
Perceptual uniformity Physiology and
Psychology
Neural networks
Theoretical computerscience
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Cosmic Splendour
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Trichromacy Theory
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CIE L*a*b* in Actual Terms
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The Line of Purples