How to make cyan color

Composition of colors

Publication: 4.8.2008
Origin: Sonnentaler, Berlin

If you take a close look at a television or computer screen (ideally with the help of a very good magnifying glass), you will find that its image consists of a large number of individual points and that these points themselves consist of three different colored points Dots (or lines) in the colors red, green and blue are composed. If you look at a point in the picture that is white, all the smallest dots of color there are equally bright. So white is obtained from a mixture of red, green and blue (all of the same strength).

Fig. 1: Luminous dots on a computer screen
(Source: Luís Flávio Loureiro dos Santos, Wikimedia Commons, CC BY 3.0)

But anyone who has ever mixed colors, e.g. B. when inks, will protest immediately: If you mix red, green and blue when inks, you will not get white, but a dark brownish color!

How can one explain these contradicting observations? You have to take into account that the television or computer screen is a primary light source, i.e. an object that generates light itself (you can also see the television in the dark), while the ink colors are secondary light sources: they only cast part of the incident light back again. For the mix of "Light colors" and "Body colors" (Item colors) different rules apply.

If you think about it more closely, this is not at all surprising. Seems like B. red and green light on our eyes, then both the sensory cells of the retina (cones) that are sensitive to red and green light are excited and send a signal to our brain. The brain interprets this as yellow light. The brightness is of course greater than if you had just looked at the red or green light individually.

If, on the other hand, you consider a mixture of the two ink colors red and green, only the light that is not absorbed by one of the pigments in the mixture is reflected back, i.e. only the light that reflects both the red and the green color becomes. Of course, this is less light than would have been reflected by each of the individual colors: The overall impression is therefore a "darker" color.

Because of this, the mixture of the colors of the light coming from primary light sources is called "additive color synthesis" while color synthesis by secondary light sources is referred to as "subtractive color synthesis" is referred to. In the first case, light of different colors ("light colors") is combined, in the second case different colors (corresponding to the pigments in the ink) are filtered out of white light ("body colors").

Additive color synthesis

In additive color synthesis, red, green and blue are assumed to be the "primary colors". These each cover about a third of the spectrum of visible light and correspond to the color ranges to which the different types of cones (color-sensitive light receptors) of the human eye are sensitive.

Additive color synthesis can be explored experimentally by directing three lamps, each emitting light of one of these colors, onto a white surface and varying the intensities of the individual lamps.

Fig. 2: Color overlay in additive color synthesis

When red, green and blue light of the same intensity is superimposed, white is obtained, as already described. An evenly reduced intensity of all three colors results in different shades of gray and the complete absence of light black.

The superposition of red and green alone produces yellow, that of red and blue produces magenta, and that of green and blue produces cyan. Other colors are obtained by superimposing two or three basic colors, although these do not all have the same intensity. So z. B. Orange, if you add red and green, whereby the green light has only about half the intensity of the red light.

Subtractive color synthesis

The easiest way to explore subtractive color mixing is to mix India ink or oil. But you can also hold filters of different colors in front of a white lamp, one behind the other, which then do not let part of the components of the white light through, so to speak "subtract" them from white.

Even with subtractive color mixing, it is sufficient to use three basic colors. The colors magenta, cyan and yellow are used here. If you have ever replaced the color cartridges in a color inkjet printer, these colors should look familiar to you (however, these printers usually also contain a black cartridge, but this is not absolutely necessary and serves in particular to save costs).

Fig. 3: Color overlay in subtractive color synthesis

So if you mix z. B. Ink of the colors magenta, cyan and yellow, you get black ink. A mixture of magenta and yellow results in red ink, magenta and cyan in blue ink, and a mixture of cyan and yellow only reflects green light. Other colors are obtained by adding different amounts of the three basic colors.

If black could only be achieved with additive color synthesis by switching off all the lights, with subtractive color synthesis you can only get white if you don't "filter out" any light at all. H. does not apply paint to the white sheet of paper. If you paint on colored paper (or accidentally paint over a spot that should remain white), then you cannot achieve white with the three basic colors; instead, you have to use a special material that reflects all incident light back - that's why you are allowed to the opaque white is not missing in the ink box.

Last update: October 18, 2017

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