GEK1532 History of Colour

8/6/2019 GEK1532 History of Colour

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GEK1532

History of color theory and color mixing

The history of color is the history of science and the interactions between different

disciplines which include philosophy, physics, physiology, psychology, chemistry andbiology but as well the arts like painting and poetry.

Thorsten Wohland

Dep. Of Chemistry

S8-3-6

Tel.: 6516 1248

E-mail: [email protected]


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Whatiscolor?

Revision:

Is it a property of objects?

Is it a property of light?

Is it a property of our brain?

Is it a property determined by our cultural background?

Is it a property determined by our language?


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Revision: Lets ask what is

necessary to perceive color Light as the medium that transfers information to us

(light source)

An object which interacts with the light and changes itscharacteristics (wavelength, intensity) and is thus

perceived Eyes that act as a sensor for light (intensity and some

wavelength discrimination)

The brain that interprets the signal detected by the

eyes and leads to the perception of the color andobject

It turns out that every single aspect here has an influence on the color seen

and color is not simply characterized by and one of them.


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How do we perceive objects?

560 BC: Pythagoreans believe that the eye sends rays to objects to obtain

information.

480 BC: Empedocles thinks that objects emit images that interact with

emanations form the eye.

450 to 300 BC: Socrates, Democritus (atomists), Plato, Aristotle, Euclid all havesome theory that postulate rays from the eye and/or rays from the object that

causes us to see color and shape.

80 BC: Lucretius postulates that sunlight acts in the air to create the

impressions we get of objects..

Up to 1200 AD: Roger Bacon still believes that it is the eye that emits rays to

scan objects.


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How do we perceive objects?

Scanning an object to obtain an

image. That is actually a concept

used in many modern

microscopes.

Pro: How can a mountain

send out images in all

directions that then can

enter the small eye?

Contra: Why are vision

rays not active in the

dark?

Vision Rays?


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How many colors are needed to

mix all possible colors?

However, remember the afterimages you saw last lecture: they suggest

that there are at least two pairs of complementary colors: yellow-blue and

red-green.

Nassau, Fig. 1.1

Aristotles color circle

6 colors?


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6 colors?An interesting article to Goethe and Newton can be found at:http://www.aip.org/pt/vol-55/iss-7/p43.html

Johann Wolfgang Goethe: He contributed to color theory (often in enmity

towards Newton) and created a symmetric color circle with 6 colors (not 7 like

Newtons) which were pair-wise complementary colors.


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3 colors?

James Clerk Maxwell

1831-1879

We are capable of feeling three different color

sensations. Light of different kinds excites these

sensations in different proportions, and it is by the

different combinations of these three primary sensations

that all the varieties of visible color are produced.

First color pictures by photographing a subject with

filters of the three primary colors.

-> Maxwells color triangle


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Blue

Green

Red

CyanYellow

Magenta

White


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4 colors?

Ewald Hering

1834-1918

We have three channels for distinguishing

colors in our brain:

2 chromatic:RED - GREEN

YELLOW BLUE

1 achromatic:

BLACK WHITE


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Saturation, hue, brightness

Hue

Saturation Brightness

Hue


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Saturation, hue, brightnessBrightness

Saturation

Hue: Blue

(HSB:241)

Sa

tura

tion

Br

igh

tne

ss


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Saturation, hue, brightness


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Newtons experiment

All these colors are said to have the

same hue but different saturation

(sometimes called chroma orpurity).

Colors obtained by passing white light

through a prism are the so-called

spectral hues or colors in the pure

spectrum.

More colors can be produced by mixingthese colors with white (ex.: red+white

-> pink).

http://physics.hallym.ac.kr

1643-1727: Newton used a prism todecompose sunlight in its parts. He founded

a color theory and made the first color circle

to order colors.


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How are colors produced in our

environment?

1) Light sources of different color can be used to illuminate objects, i.e. one uses

only a selected part of the visible spectrum for illumination.

2) A part of the spectrum is removed

Assuming Sun light as the light source. The sunlight interacts with the object and:

400 nm 500 nm 600 nm 700 nm

3) The sunlight is separated in its components (prism, rainbow)

Start with no light, i.e. darkness

4) A part of the spectrum is added (emission, e.g. fluorescence)


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Spectrum What you seeAdditive mixing


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Spectrum What you seeSubtractive mixing

Light source is needed


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Spectrum What you seeSubtractive mixing

An object that reflects all light is WHITE

An object that absorbs blue light isYELLOW

An object that absorbs blue and green light is ORANGE

An object that absorbs all light is BLACK


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Question for you:

Is there a possibility to test whether

two colors are really the same or

are metamers?


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So what is the minimum amount of

colors we need to mix all colors?

3


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Additive color mixing by three

primary colors

Additive color mixing is based on the emission of light.


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Example: Television


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Partitive mixing

Close up: Far away:

In contrast to simple mixing, where colors really overlap, in partitive mixing

colors do not overlap. However since they are close together our eyes are

not able to resolve them and the colors add up.


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Subtractive color mixing with three

primary colors

Subtractive color mixing is based on the absorption of light (illumination or

light source dependent).

For an article on primary colors see:htt ://www. ain.net/PIA GATF/PDF/GATF/info005. df


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Lets try an experiment


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Questions to ponder

Why do you see the colors only at the

edges?

How does the colors depend on the edge

type?

Can you explain why that is so?

For further details see: http://www.colorcube.com/articles/prism/prism.htm

GEK1532 History of Colour

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