No mention that both sets of primaries come from the biology of the average human eye, and other animals might be better served by other colors? Ok, yeah, that's not really relevant to the point the article was actually getting to, but I think it's important to remember. There's nothing magical about those colors. They effectively stimulate color receptors in our eyes such that our brains interpret the input in ways that can be combined to cover a pretty large gamut of the full range our eyes can perceive.

But as for what the article actually does focus on, I absolutely agree. You can create some really striking art by restricting your gamut to the range you can cover with a particular set of pigments.

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Hobadee 4 days ago | parent | next [-]

In addition to this, there will always be 2 sets of "primary" colors for a given eye: Additive and Subtractive.

Additive primary colors are necessary when you have no light, and need to create color. Think a black screen, and you are creating colors with RGB pixels.

Subtractive primary colors are necessary when you have full-spectrum (white) light and need to filter down to a single color.

Other "primary" colors, such as the red, blue, yellow pigment primaries we learned in Kindergarten exist because pigments historical couldn't be created perfectly, and those "primaries" are the best way of getting the most colors, but still have a very limited (by comparison) gamut.

	▲	kurthr 4 days ago \| parent \| next [-]
		Yes, one challenge with defining Subtractive primaries is that they are dependent on the white point of the "white" light source (e.g. D65 vs D50). While this seems inconvenient, it's worth noting that the apparent color of greys for Additive primaries is also dependent on surrounding illumination. So primaries are useful for generating roughly orthogonal changes in perceived color, but they don't tell you how they will be perceived in absolute terms without knowing surrounding illumination. In the simplest case, asking if something is bright (even without color) is impossible without knowing the surroundings.
	▲	Diggsey 4 days ago \| parent \| prev [-]
		> There will always be 2 sets of "primary" colors for a given eye: Additive and Subtractive. If your eye only has two types of cone cells then your additive and subtractive primaries are the same ;)

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gizmo686 4 days ago | parent | prev [-]

I think that understanding how eyes and light work is very informative on this subject.

Why are there 3 primary colors (regardless of which 3 you pick)? That has nothing to do with the nature of light, and everything to do with the fact that humans see light using 3 distinct frequency response curves [0]. This means that humans perceive color as a 3 dimensional space; and the role of the primary colors is to pick a point in this space by selectively stimulating or masking the 3 response curves. In a world of pure linear algebra, almost any 3 colors would do, but physical reality limits how ideally we can mix them; and how much light they can emit/mask.

Further, the 3 response curves are overlapping, so there is no set of ideal colors that would let you actually control the 3 curves independently.

[0] At least for color perception in a typical human.

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adrian_b 4 days ago | parent | next [-]

Besides having 3 primary kinds of photoreceptors, there are additional complications caused by the initial processing of the color information in the visual system.

Besides the 3 primary color sensations from the red, green & blue receptors, there are a few dedicated detectors for some colors.

Yellow is detected when red is equal to green and both have a high enough brightness. White is detected when red, green & blue are equal and all have a high enough brightness. While black could be detected later, by the lack of information on the other channels, it seems that it also has a dedicated detector.

This gives 6 primary color sensations, where the colors are not perceived as a mixture of colors, like it is the case for orange, blue-green, violet, purple or gray. Presumably these 6 colors correspond to separate outputs of the initial color processing stage of the visual system.

I do not know whether this is true, but I believe that there also exists a dedicated detector for the color brown. While brown is just orange with low brightness, the "brown" sensation is very distinct and very unlike the differences perceived between e.g. dark red and light red, dark green and light green or dark blue and light blue, where the differences are perceived to be only in quantity, not in quality.

A dedicated detector for brown makes sense, because important things in the environment are brown, e.g. the ground is brown in most cases, because it is composed of a mixture of white oxides with red, yellow and black oxides of iron and manganese. Also wood is frequently brown and also many mammals are brown.

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sdeframond 4 days ago | parent | prev | next [-]

Related: some colors can only be perceived by selectively hitting the right cells with tiny lasers.

https://www.scientificamerican.com/article/researchers-disco...

	▲	8n4vidtmkvmk 4 days ago \| parent [-]
		Put this in a VR headset, and maybe they'll finally sell? Ultra HDR

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morninglight 4 days ago | parent | prev | next [-]

I am surprised that the Purkinje effect and the degree of illumination are not mentioned. For example, should the primary colors be shifted depending on illumination?

https://en.wikipedia.org/wiki/Purkinje_effect

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chowells 4 days ago | parent | prev [-]

The linear algebra argument for almost any three colors only works if you can have negative intensities. I don't know how to do that with stimulation of photoreceptors, so I don't think that applies here.