Physics of Colour Perception

8/10/2019 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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1stDecember, 2010 R Ruia College

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?


7/541stDecember, 2010 R Ruia College

What is Colour?



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



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



Observers Situation in Colour Science

OBJECT



What is Colour?



Is Colour Wavelength?



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.



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

Physics of Colour Perception

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