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Why aren't there printers red-green-blue ink cartridges?

I would like some well-documented articles on this because I haven't found anything comprehensive. The best I've found are this and this on Quora, and this article, which say either the color is too thick for the paper to handle, or too rich to produce lighter halftones.

Most others just unhelpfully delve into the distinction of "additive color model" as light-based and "subtractive color model" as pigment-based, which would make sense only if you were talking about "colored lights" and "colored pigments" as two completely separate topics. Last time I checked, yellow was in the visible spectrum, and there were definitely red pigments (I mean, if you ever dabble in art, you'd know there's at least red pastel and you can definitely use it on a white canvas).

So to be as clear as day: I'm not asking for the distinction between the RGB additive color model and the CMYK subtractive color model. I'm asking for the practicality of using a set of red-green-blue cartridges as if there were an RGB subtractive model.

After asking around a little more on other sites, I'm guessing we don't use red-green-blue inks because a practical red ink would have to be able to reflect yellow light and magenta light, otherwise you couldn't mix it with any other ink and it would be rendered wasteful because it could only print red. It's just that there's no such thing as magenta light, therefore there's no practical, usable red ink.

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    How would you expect light to be reproduced on paper? (RGB is a light spectrum color model).
    – Scott
    Commented Apr 27, 2018 at 2:44
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    RGB is light it's not "red pigment". It's a light which shows in the frequency of the red spectrum. To be more specific it reflects light at the frequency of red. There is no "pigment". Pigments are for ink, paint, et al. - physical things.
    – Scott
    Commented Apr 27, 2018 at 2:46
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    And many, many, many, many decades ago it was discovered that using Cyan, Magenta, Yellow, and Black to reproduce things in the RGB light spectrum was the closest possible way with the widest color gamut. You need to research CMYK. RGB is only light, whether you can tell it or not.
    – Scott
    Commented Apr 27, 2018 at 2:53
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    I'm voting to close this question as off-topic because the premise under which it is asked is so deeply flawed that it can not be answered in a way that will be of any practical use to anyone, including the person asking it.
    – Westside
    Commented Apr 27, 2018 at 11:50
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    Please do not close it down - it has prompted some good people to write answers (so they also thought it worth their time) and it has produced some good answers with fundamental training. I learn through "straight textbook approach" but others might benefit from "weird question" plus "good answer" format of learning. Thinking out of all those boxes, why not? Commented May 24, 2018 at 12:42

12 Answers 12

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Actually, there already exist printing systems which let you choose your colors. In screen or offset printing you can use any existing color to print something.

Now lets say we'd choose red, green and blue as printing colors. We'd still have a subtractive color system (If there's more ink on the paper, there will be less light reflected. So the color gets darker.).

Here's a possible result you could print with these colors:

An image printed with red, green and blue ink.

Remember: we're still in a substractive color system. We can only recreate colors which are mixed together with the base colors. They can be lighter if you'd halftone them. But you can't reproduce yellow for example.

Mixed together red, green and blue in a substractive color system.


So to answer your question:

There aren't any red-green-blue ink cartridges because the images you could print with them would be very limited.

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To understand why printers do not use red, green, and blue ink to reproduce color from the light spectrum, you need to research CMYK printing.

I'll avoid all the additive/subtractive explanation.

Around 1900 a printing company first incorporated cyan, magenta, yellow, and black inks into a printing press to reproduce color. Through that company's research they discovered that using these 4 specific colors millions of other colors could be reproduced via mixing, overprinting, etc.

To put it plaining, using red, green, and blue inks or pigments severely limits the actual range of colors which can be reproduced in a subtractive system such as printing. While the additive light spectrum offers millions of color for RGB, the same is not true when the three colors are used in a subtractive system.

You need to research CMYK and why it's in use as opposed to trying to find out why RGB isn't used for subtractive systems.

There is zero correlation between the RGB of the light spectrum and red-green-blue pigments.

As the old adage states -- "You can't prove a negative" --- That appears, to me, to be what you are attempting to do, or at least asking others to do.

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  • Gosh, finally you've got it. Yes what I want to ask is a hypothetical RGB subtractive model for printing (but I obviously failed to express clearly), not that it collerates to the RGB additive model or anything, because it simply does not. Commented Apr 27, 2018 at 3:39
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    Read the last sentence of the answer.....
    – Scott
    Commented Apr 27, 2018 at 3:40
  • Not that I was attempting to prove a negative or anything, but I just wonder why there aren't an RGB subtractive model, or even a CYM additive model (lol, maybe not). Commented Apr 27, 2018 at 3:44
  • Because light can't be reproduced on paper and ink can be reproduced in light. There are valid reason why printing uses CMYK and Light uses RGB -- the spectrums possible.
    – Scott
    Commented Apr 27, 2018 at 3:49
  • Dude, you got that severely limits part, I give you that with one upvote, even though I'd prefer much more detail. Maybe don't dive deep into this "light can't be reproduced on paper" thing. I'm not asking for such thing as "printing light on paper" or even remotely "representing the full range of light color on paper". Commented Apr 27, 2018 at 3:53
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Introduction

To understand this we need to look at the entire system. The system consists of at least 3 parts: the observers brain, light transfer to the eye and the technical system from where it came.

Central to part to how light works is in the eye transfer. If we cut corners a bit, so that we can have a discussion at a reasonable length, one can say that the human eye senses R, G and B colors.

Closer look at a perfect technical system

Due to the way the eye works you need to reach it with a signal of a very specific Red, Green and Blue color. Nothing else matters for the brain. This is relatively straight forward if you send light directly, like in a monitor or a led lamp.

But print does not do this, what it essentially does is it removes color from a white color source with filters. So you are now not controlling the colors that reach the brain directly, your controlling them indirectly.

Clarification due to confusion: Printers currently in use are unable to mix color! What they do instead is they overlay 3 semitransparent layers on top of each other. This makes the process cheap and easy. So the colors chosen can not block each other.

So what you technically want is 3 filters that allow you to individually control each channel of the primaries. These channels are mathematical inverses of RGB so the first filters needed are:

  • Absence of red
  • Absence of green
  • Absence of blue

If you now search these you get that these colors are in fact Cyan, Magenta and Yellow. This is in fact best we can do, but thats me saying so not motivating this thing in anyway.

So to clear this out lets observe whet happens when you have a red color and eventually mix it with say blue. Your paper/light is white which is all 3 components together. So you remove Green and Blue. Note how this color removes 2 channels. Now Blue also removes 2 colors, Red and Green. So if you assume these colors can be overlaid perfectly mixing red and blue becomes.

  • For red:
    • Absence of Blue
    • Absence of Green
  • For blue:
    • Absence of Red
    • Absence of Green

Which results in absence of all color which we in layman's terms call black. Obviously this wouldn't really happen exactly if the pigments weren't perfect, but things would get muddy really fast and you would find it impossible to find bright intermediate colors.

You see the color model is tied to the exact, best 3 color, technical system we have. And probably can ever hope to have.

Closer look at a a real technical system

Remember when i said that there are 3 parts in the system, I've neglected one of them. Up until now we have assumed that the mathematics make sense. But it does not quite work that way due to physics of light.

It turns out that the magenta color does not exist, except in our brain. A spectrum does not have a magenta component. See the spectrum does not wrap back up to red form the blue-violet end it just keeps going we just don't see it.

So this means that Magenta is always a mix of 2 things. But before this I said that each perfect color must have the property that is only deletes one range. Well magenta can come close but can never really manage this. This is why CMY color has so big troubles in the blue-green color ranges (also slightly in oranges). Yellow and Cyan does not really have this limitation.

Finding good pigments also a bit hard so the CMY color space always a bit muted and a bit limited due to technical factors. But its pretty good.

But couldn't we choose another 3 colors? Well, if colors worked like any other vector entity like position and velocity for example that would be easy. But alas the human eye is a fixed target it wont help. We can not find any better 3 colors than CMY.

Nothing prevents use form having more colors though so you could certainly fix most of the limitations by having 5 (adding the troublesome green and orange for example) colors plus black, or even better more. But without having negative color at our disposal, we can not do better with 3 colors on a print.

On that note

Its not entirely out of the question that print might not come up with some other method than pigments. Because if it would be possible to create with print methods interference patterns, then it would be possible to make the surface send out red even if its entirely passive so it MIGHT be possible to make it work just like a monitor even if it is a reflection.

Hologram tech can certainly do so to certain extent. So its not really technically totally out of the question just out of the question with current tech.

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  • @Vun-HughVaw Yeah but human eyes are not spectrometers. We see yellow when you send a signal to Red and green sensor (you can thus send yellow or red and green or any combo thereof all same to us). Color as precieved by the brain is not a spectral quality.
    – joojaa
    Commented Apr 30, 2018 at 4:37
  • @Vun-HughVaw By the way things that have different spectra but look the same are called metamers.
    – joojaa
    Commented Apr 30, 2018 at 4:45
  • Now that I looked at your answer again with fresh eyes, all you were basically said is "because that's how the human eye work, we have some kind of fixed targets on CYM." You mentioned how magenta works, but still did not why cyan and yellow work as well, because "targets" I guess. Commented Apr 29, 2023 at 17:23
  • @Vun-HughVaw Ok, no actualy or fixed targets are closer to RGB. You can see how the targets called cones react to wavelength here. Notice that magenta wavelength does not exist. Its just simply how a distribution with red and blue color parts get percieved by our brain.
    – joojaa
    Commented Apr 29, 2023 at 17:32
  • OK, why do YELLOW AND CYAN work then? At this point I'm painfully aware that magenta wavelengths do not exist (I even double-checked if I happened to miss the link specifically about this in my answer, and I did not). In fact it's just not the color called "magenta", but a whole range of mixtures formed by combinations of wavelengths at the two ends of the spectrum. I got it. Tell me how you think YELLOW AND CYAN work as regards ALL THREE colors of the CYM model. Commented Apr 29, 2023 at 17:37
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CMY are the inverse of RGB. A film negative of an R filtered image is basically the C plate.

They are inverted specifically for the reason mentioned in the other answers: paper reflectivity vs. additive color mixing.

It is obvious that one can use three plates inked for RGB, but the fact is, it isn't done because it is simply not commercially viable, mostly because mixing such halftones will wind up with "mud colors." CMYK is used because it can reliably reproduce a very large subset of the required color gamut without adding extra plates and costing more money.

For non-CMYK printing systems, check out serigraphs and silkscreens.

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The 'light spectrum' from a prism is RGB. It needs a light source. That is why it is used to create monitors, TVs, phones, etc. CMYK is from the printing industry and is about 'reflective spectrum' of inks that reflect off a surface (or through if printed behind a transparency). It mimics RBG to the human eye.

Look up; RGB color model. and CMYK color model on Wikipedia.

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    What am I missing? I went to art school, and switched to Graphic Design. Your question is, "Why aren't there printers red-green-blue ink cartridges?" There may come a day when a material can be 'printed' in RGB. That is not the case, yet. Perhaps when you will be one of the first to approach it. All new discoveries started with a "how come? question. Commented Apr 27, 2018 at 3:18
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    @Norman, you aren't missing anything
    – Scott
    Commented Apr 27, 2018 at 3:19
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    @NormanEdward Yes, you are. I'm not looking for the distinction between the color models themselves, which is what you've given. I'm looking for the reason why there aren't printers that use red-green-blue ink cartridges for printing. This is not a question about the physics of light as colored light vs light as colored light absorbed or reflected by pigment. It's about the practicality of using different sets of inks (red-green-blue vs cyan-magenta-yellow-black) Commented Apr 27, 2018 at 3:28
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    Your question is perfectly logical to you. But, you dismiss light RGB's source as occurring FROM light. Inks are reflective. If you attempt to print RGB, you will find a lack of depth and shadowing in the image the K (Key color/black) provides. RGB inks would have that same problem. As a LIGHT source, RGB creates it's own shadows. Commented Apr 27, 2018 at 3:35
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    @Vun-HughVaw perhaps it's you that is missing something.
    – Scott
    Commented Apr 27, 2018 at 3:35
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No theoretical reasons make RGB printer impossible. It's only impractical.

How?

Have black paper. Print on it fully opaque red, green and blue ink dots, preferably rectangular ones to get more cover and brighter image with less light. Be sure that the inks do not overlap. That's difficult, but this is already said to be impractical.

Leave inkless just that portion of the paper which amount you want to reduce the brightness from the maximum. Watch the image in so bright white light that the areas of paper reflect as much R, G and B as you need to see it well. That's as much as RGB monitors glow. Impractical? Yes, as I already said.

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  • Yeah you wouldn't get enough brightness when you need to mix things. So your paper would have to glow, which isnt out of the question with some fancy future tech.
    – joojaa
    Commented Apr 29, 2023 at 18:17
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Red, Green, and Blue ink cannot generate a full spectrum of colors through an additive process. However, there are special print processes that do use R,G,B except they are much more expensive both for paper and the equipment.

The oldest and most well known is Durst Lambda C-Type Prints which is used for making Chromogenic Prints

Images are produced by exposing light sensitive material with RGB laser light which is then developed through the relevant chemical process.

There are also companies developing new processes to update this such as Lumejet coining theirs the L-Type Print.

An inkless process, the LumeJet S200 prints on 305 mm wide rolls of photographic paper, cut in lengths from 200mm to 1000mm. Using RGB colourspace, the LumeJet S200 is ICC profiled and achieves amazing colour fidelity, including hard-to-print Pantone® spot colours like reflex blue, neons, metallics and pastels, not to mention amazing blacks.

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  1. The colors red, green and blue are considered primary colors because they are the ones that the eye detects (long-wavelength sensitive, middle-wavelength sensitive, and short-wavelength sensitive). So, RGB is not a matter of taste only, but it has a direct link to how we perceive color.

  2. Using red, green and blue as pigments:
    2a) A red pigment will reflect red, while it filters green and blue. So, it bounces back 1 primary light color and blocks 2.
    2b) So, let's add another layer of color pigment on top of it, say, green. The green pigment will bounce off green light, while filtering out red and blue.
    2c) But the green light was already filtered in point 2a. That's why all the light is filtered out (theoretically).

  3. Using cyan, magenta and yellow as pigments:
    3a) A cyan pigment will bounce blue and green light, while filtering out red light. So, it bounces back 2 primary colors and filters 1.
    3b) Let's add another layer of color pigment on top of it, say magenta. The magenta pigment will bounce back the colors blue and red, while filtering out the green.
    3c) So, red light was filtered out at point 3a, and green light was filtered out at point 3b. But blue light is still bouncing. So, you have 2 layers of pigments, but 1 color is still showing.

  4. As you can see, part 2 is more limiting than part 3.

  5. So, to sum up, Red, Green and Blue, block more light than Cyan, Magenta and Yellow (and that's why they look lighter in their most pure state). And you need them to block less light to be able to reproduce more colors.

  6. This is all in theory, pigments aren't perfect, neither are our eyes, so it's much more complex than that.

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I don't believe I am answering this after all the comments.

Because Red, green and Blue are secondary colors. And for a printer to be able to print a richer range of colors you want to use the purest primary pigments you can find.


Actually, there were systems that used Green and Orange in the past, but they were used to expand the range of the basic CMYK print, but these days the pigments are so good that the hexachrome system was closed.


For actual examples on how a print using RGB inks would look, here I made some simulations: https://photo.stackexchange.com/questions/128616/why-is-cmyk-more-efficient-beneficial-than-rgb-for-performing-printing-operation/128621#128621

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The reason is to do with lightness.

Light is radiation and if we look at the classic spectrum of visible light, from left to right, we see the colours changing from red to yellow to green to blue to purple as the wavelength of the radiation reduces. Yellow is between red and green so if we mix red and green paint, or ink, we get yellow. Ditto yellow and blue giving green. The problem is that some colours are lighter than others, irrespective of where they lie along the spectrum. Yellow for example is a light colour: much lighter than say red or green which lie to either side of it in the spectrum. This means that when you mix red and green paint, or ink, although you'll end up with yellow, it'll be a darkish yellow: like mud. You need to add a bit of white paint if you want a lighter yellow. The truth is that wavelength ignores the fact that we all consider dark yellow as being a different colour than light or medium yellow.

Since there are an infinite number of different colours between one end of the spectrum and the other, things were been made easier for early paint manufactures in that they produced a reduced set of colours. At the easiest level they simply divided the spectrum into three sections (reddish colours, greenish ones and bluish ones - referred to traditionally as the "three primary colours"). An artist or decorator could buy these three colours and mix them to produce every colour in the spectrum - provided of course that they also buy a tin or white paint to add lightness and therefore produce every 'shade' of colour too. In reality, paint manufacturers produce not just three but a whole range of colours for the convenience of their customers i.e. relieving them of having to mix paint.

In the computer printer world, rather than have to produce white ink (which isn't needed anyway because all colour print-outs are on white paper) ink manufacturers decided to split the spectrum into a different set of three sections so that one colour is quite light, another quite dark and the third of medium lightness i.e. yellow, magenta and cyan. You'll see them in the spectrum equally spaced out. This choice of three colours simply minimises the amount of ink-mixing required of the printer, on average.

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    This answer is factually incorrect. The traditional primary colours used in painting are red, yellow and blue. You can't make a light shade of yellow using red, green and white paint - that would only make a light brown, not yellow.
    – Billy Kerr
    Commented May 9, 2020 at 9:19
  • It is important to understand that light spectrum and colors humans see are not the same thing. Printing technology can not alter spectrum in ant way
    – joojaa
    Commented May 9, 2020 at 14:02
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I still think it's about lightness. After all, in order to produce light colours you need to spray ink thinly across the white paper. Unfortunately the mechanical limitations of inkjet spraying would cause graininess if we were to use inks of red, blue and green rather than the lighter shades of yellow, cyan and magenta. In the end, it's still simply a matter of coloured light beams merging on their way to hitting the backs of our eyes.

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    No amount of red, green, and/or blue ink will result in yellow. It will only produce very light red, green, or blue. Which is exactly how you'd print "pink": red ink sprayed thinly on white paper. It will not turn into any other basic color (green, blue: cyan, yellow, orange, purple, or anything else).
    – Jongware
    Commented Jun 8, 2020 at 17:14
  • Look at theyve's answer: you can't obtain yellow from RGB inks. The only way to obtain yellow from inks is to print with yellow ink.
    – Luciano
    Commented Jun 11, 2020 at 15:19
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This question was asked ages ago. I'm a much wiser person now, so I'm gonna throw my two cents' hat in the ring.

First of all, let's address the the additive vs subtractive (or light vs pigment) debate that many answerers had expertly explained in various highly unassuming, specific and instructive ways. Hopefully, once and for all.

The whole deal with mixing paints or inks is that they contain pigments, which absorb light. The simple reason that a red ink appears red is because that red ink absorbs mostly all colored light waves, except the red ones (and yes, "white" light isn't white, it's ALL the colors). When you shine white light on a red ink, it absorbs all the "hidden" waves that are green, blue, purple, etc., and reflects only the red ones, and all that reflected red reaches your eye, and you see the ink as red. That's just how pigments work.

As for light, you just mix different red, green, blue wavelengths together. Neither absorption nor reflection need be involved. Mixing light is "additive mixing". Mixing pigments is "subtractive-additive" (subtractive mixing because of absorption, "subtracting" from white light, and additive mixing happens during reflection)

A major implication of this fact is that, if you mix two or more inks together, you might end up with no reflected light at all. Think about it, if a red ink only reflects red light, and a yellow ink only reflects yellow light, what happens when they're mixed together? Black, of course. The red ink will absorb all the yellow reflected by the yellow ink, and the yellow ink will absorb all the red reflected by the red ink. So there's nothing reflected at all, and what you get is black, the absence of light.

But to this point, you might correctly respond, "OK, smarty pants, if that's how it works, then how come I still got orange by mixing red ink and yellow ink?" Fair point, because what I mentioned above is, ideally, how it should work. But the real world is very messy. That means the idea of a red ink that only reflects red light is nothing but a preposterous fantasy. So is the idea of a yellow ink that only reflects yellow light.

In reality, you rarely ever get anything approaching black. The best you can get is a dark brownish color by mixing red ink and green ink, or a dark purplish color by mixing red ink and blue ink. But still, why does red plus yellow equal orange, and oftentimes, a rather bright orange at that? The answer lies in the overlap between the reflectance range of red inks and yellow inks. Let's take a look at a simplified reflectance graph of various pigments used to make inks, paints, dyes, etc. Reflectance, or the amount of specific colored light reflected by a pigment, was measured relatively to a sample white pigment weighted as 100%.

enter image description here (Graph made with the program Graph, with data from chsopensource.org)

Clearly it's never black and white that one pigment only reflects one type of light. There's huge overlap between cadmium red and cadmium yellow. Turns out, despite their appearances, both these pigments reflect quite a lot of wavelengths in the red-orange area as well, which explains why you get orange by mixing red and yellow PIGMENTS.

So, if pigments actually have ranges of colors to reflect, for a pigment to be a good mixer, the key is bandwidth. The broader a pigment's bandwidth is, the more different colors it can reflect, the better it can mix with other pigments as losslessly as possible.

For this reason, red, green and blue pigments are the worst choices imaginable. See, not all colors on the visible spectrum are created equal. The three so-called primaries, take up huge chunks of it. Check out this Wikipedia article for more detail, but the gist is that red, green and blue are highly broadband colors, taking up bands of upwards of 65 nm.

Here's where I have some bad news, I can't explain exactly why. But it does seem there's somewhat of a limit to how broad a pigment's bandwidth can be. If you could just imagine that a given physical pigment can only reflect so many different wavelengths, then if a color occupies too many wavelengths, there won't be enough room for other colors, for that pigment to reflect. A red ink and a green ink would make a horrible brownish mix, not because red is the "complementary" of green or some nonsense like that, but because there's simply no red and green pigments in existence with bandwidth large enough to overlap. If there were, you would probably end up with a yellowish mix, the same way you mix a red and a green light together. Likewise, a mixture of red and blue pigments would be horrendous, not only because it's basically impossible for them to overlap in any acceptable way, but because blue pigments are inherently dark (which is inherent to the color blue itself, it's just a dark color). Looking back at the above graph, you can clearly see ultramarine blue's pitiful reflectance.

Meanwhile, compared to red, green and blue, the bandwidths of cyan, magenta and yellow are much more favorable for how narrow they are (downwards of 25 nm). So there's more room for other colors, so to speak. Magenta, or any purplish colors for that matter, occur in excellent mixing pigments because their bandwidth is literally 0 nm. Any magenta or purplish pigment has reflectance coverage of colors in both the short end (violet-blue) and the long end (red-orange) on the visible spectrum. Cyan pigments cover both green and blue, and yellow pigments cover both red and green. This is why, among the three so-called "artist's primaries," yellow carries the entire team, while red and blue have to rely on their respectively "cool red" (basically magenta) and "warm blue" (basically cyan) neighbors on the spectrum.

Despite their shortcomings, red and blue inks are still found in high-end photo printers, for their importance. A red mixed from yellow and magenta is always inferior to a genuine-article red. On the other hand, it does seem challenging to produce a satisfying magenta ink since their typical variety often result in an overly purplish red.

So long answer short, printers only mix three inks to cover as many colors as possible. To do so, they necessarily need pigments that have broad coverage of different colors, namely yellows, cyans, and especially magentas. Red, green and blue pigments are physically incapable of providing such coverage.

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  • No! This is not how it works, Percieved color is not directly linked to wavelength. while a wavelength has a color it does not follow that all colors are wavelengths. Simply more about how the human sensor works. Simply you dont beed a orange wavelength for a human to see orange all you really need is to M and L color cones to react to it. So at the end human eyes arent spectrometers.
    – joojaa
    Commented Apr 29, 2023 at 16:36
  • and yes I agree just saying additive and subtractive color model does not tell anything.
    – joojaa
    Commented Apr 29, 2023 at 16:39
  • @joojaa It's easy to scream "This is not how it works," and I'm done with this kind of expert advice. I was done with it, filled with nothing but frustration and rage induced by the borderline useless answers, 5 years ago when I asked this question, and I'm certainly done with it now. I gave my sources and how I interpreted it. There's actually a paper specifically mentioning "broadband" and "narrowbrand," but it was too offhand and had little explanatory power, so I didn't include it here. Commented Apr 29, 2023 at 17:09
  • @joojaa If you want to prove you're right, feel free to include some sources in a coherent answer instead of whatever you're doing here. Commented Apr 29, 2023 at 17:11
  • i can add relevant links. and your not entirely wrong, your just missing one piece of the puzzle. Because of the way the way the site works its not possible to do this unless we open a new question or move over to chat.
    – joojaa
    Commented Apr 29, 2023 at 17:20

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