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Subtractive Systems

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Subtractive Systems (CMY and CMYB)


Actually, the painters don’t work with immaterial lights, but with material pigments. Why having talked about lights for such a long time? Because from NOW on, the subtractive systems will be much easier to understand when you already know the additive one. (The former theoreticians didn’t know this additive system. That’s one of the reasons why they couldn’t imagine a correct color theory.)

The three basic colored pigments aren’t Red, Yellow and Blue any more — I already said it above. The subtractive primary colors are Magenta, Yellow and Cyan, PRECISELY the same as the additive secondaries. That’s the CMY system (CMY for Cyan, Magenta, Yellow).

IN THEORY, mixing Magenta and Yellow gives Red, Yellow and Cyan gives Green, Cyan and Magenta gives Blue. Mixing the three primaries together should give black. Thus, the additive secondaries are the subtractive primaries and conversely the additive primaries are the subtractive secondaries.

Here are some images which briefly resume the similarities and the differences between the theory and the practice in both additive and subtractive systems.

They demonstrate that, if the additive system is a perfect one, where the theory and the practice are identical, it is absolutely not the case with the subtractive systems. Hence the difficulty of establishing a correct color theory for those who did not know the additive system in the past centuries.

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1. The theory

Figure #1: The theory 1 — Primaries

Figure #1 illustrates the foundations of the theory. The first drawing shows the RGB system with its 3 additive primaries, Red, Green and Blue. The addition of the three primaries, obtained by projecting their colored lights together on the same white screen, gives a white light.

The second drawing concerns the CMY system with its 3 subtractive primaries, Cyan, Magenta and Yellow. In theory, when subtracting these 3 colors (e.g. by mixing together 3 colored printer’s inks) you should obtain black — but in a few moments we will see that, unfortunately, it is not so in the practice.

Fig. #1
theoretical primaries

For better seeing all the images of this page, simply click on them

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Figure #2: The theory 2 — Secondaries and tertiaries

The first drawing shows that the RGB primaries are the CMY secondaries and vice-versa. The second one shows that, in both RGB and CMY systems, when you mix together two adjacent colors, i.e. every time a primary with a secondary one, you obtain a tertiary color. For example, Blue (primary in the RGB system, secondary in the CMY system) mixed with Magenta (secondary in the RGB system, primary in the CMY system) produces Violet, tertiary color in both systems. The same for Red and Yellow giving Orange, etc.

Fig. #2
theoretical secondaries and tertiaries

OK. That’s the theory. But now, let’s see what happens in the practice.

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2. The practice

Actually, in the CMY system, the theory and the practice differ more or less considerably, because the chemistry has not been able yet to produce primary pigments perfect from this viewpoint, particularly for the printing industry — but it’s the same thing with any colors for artists. Actually, printing inks exist in different sets of primaries. Often:

  1. Yellow is good or a little too dark;
  2. Magenta is not bright enough;
  3. Cyan is too dark too.

The first consequence is that you cannot get a pure bright blue: it is either too dark, either too mauve, or both. The other two secondary colors are a little too dark too, but this is not very important.

The second consequence is that you cannot get black too. Mixing the three primaries gives a dirty brown. That’s why the printing technicians have added a fourth color: black. That’s the CMYB system (CMYB for Cyan, Magenta, Yellow, Black).

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Figure #3: The practice 1 — RGB system

Figure #3 shows us that — with the RGB system — the practice gives the same results that were predicted by the theory. The 3 additive primaries can give us 3 secondaries and white, and the six primaries and secondaries mixed all together give us white too.

Fig. #3
RGB system in the practice

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Figure #4: The practice 2 — CMY system

The first drawing shows two things.

  1. The 3 primaries are not as bright as expected by the theory. The dyestuffs of the printer’s inks as much as the pigments of oil colors are not perfect for color synthesis. Actually, modern chemistry hasn’t yet been able to produce quite appropriate dyestuffs or pigments for the subtractive CMY system. The result is that the 3 subtractive primaries are duller and less beautiful than their corresponding secondaries in the additive RGB system.
  2. The consequence is that when you mix together these 3 subtractive primaries, you don’t have black — as predicted by the theory — but only brown.
Fig. #4
CMY system in the practice

The second drawing shows the CMY secondaries. You’ll immediatly note that these secondaries are not as good either as the corresponding primaries of the RGB system. Particularly Blue, which is at the same time too dark and too violet.

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Figure #5: The practice 3 — CMYB system

The figure #5 concerns the CMYB printing system, i.e. the system that adds black to the three subtractive primaries.

Fig. #5
CMYB system in the practice

On the first drawing you see its three primaries and its three secondaries, identical to those of the CMY system. The second drawing shows the complete CMYB system, with its primary, secondary and tertiary colors. You will observe too that the real tertiaries, like the other colors of this system, are less bright and more dull than the theoretical ones.

But now you can get good blacks and grays.

To sum up, the subtractive system is unable to reproduce most bright colors.

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What about the painter?

Definitely, trying to execute a painting with only three colored pigments (subtractive primaries) can be a very interesting exercise for an oil painter, but in the practice he enjoys the use of several bright colors. He is thus able to reproduce a whole range of colors, much more than the printing industry.

For example, the artist has at his disposal some blues that are really blue — Cobalt Blue and French Ultramarine — and very bright roses and violets, not to mention brilliant yellows, oranges and reds and nearly spectral cold greens like Viridian and Phthalo Green. However, there exist no perfect Magenta nor Cyan among the really permanent and lightfast pigments.

In fact, the painter doesn’t really need to possess perfect subtractive primary pigments, because he can easily make nearly any blue, green or violet with the existing pigments. Mixing Quinacridone Magenta and French Ultramarine will give very interesting violets, but never a bright one like Cobalt Violet Light. But it’s no problem for him: he can easily use the pure Cobalt one. And so on. However, it remains impossible to paint every color of the nature with oils, what we will examine in the next page.

(Back to Pigments No. 3, Painting with Primary Colors)

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