primary colors are subjective?

For color photography the primaries are red, blue, and green. For brush painters they are red, blue, and yellow. Why are not primaries the same for both? - David Lyga

And, no, I do not like the new 'home page' format for apug.org.

As colour is determined by light, the primary colours are Red, Blue and Green which, in various combinations, produce all of the colours that we can see.

Most people when they learn about art in school are taught that the primary colours are Red, Blue and Yellow. This is completely incorrect. What should be taught is that the primary pigments are Red, Blue and Yellow. Each reflects a different parts of the visible light spectrum and, by combining them in various ways, you can create different pigments that reflect most of the visible light spectrum.

David
www.dsallen.de

Light is additive, pigment is subtractive.

Mix the primary colours of light together and you get white. Mix the primary colour pigments together and it's (close to) black.


Steve.

David Allen said:

As colour is determined by light, the primary colours are Red, Blue and Green which, in various combinations, produce all of the colours that we can see.

Most people when they learn about art in school are taught that the primary colours are Red, Blue and Yellow. This is completely incorrect. What should be taught is that the primary pigments are Red, Blue and Yellow. Each reflects a different parts of the visible light spectrum and, by combining them in various ways, you can create different pigments that reflect most of the visible light spectrum.

David
www.dsallen.de

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At the school I am at we have a class called color studies where this is discussed. We also talk about it in painting. So, it is not taught incorrectly or at least not in the art department I am at.

It all depends on whether you are talking about colors of pigment or colors of light or whether you are talking about additive colors or subtractive colors.

With all the "Ifs," "ands," "buts" and "ors" it seems like a big game of Fizzbin!

Here's an interesting (I hope) tidbit. I worked in the printing industry back in the 60s. the color presses had fountains for red, blue, yellow, and black inks. The idea being that those inks would come together when printing color separation and produce full color. But the cans of ink for this purpose were called process red, process blue and process yellow. When one actually looked at those inks, it was obvious that the process red was magenta, and the process blue was cyan. The process yellow was just a very pure bright yellow. I think the pressmen, who did a good job of making everything look good while supervising the the running of these giant presses, weren't schooled in color theory, so the industry just named those colors in a generic way.

Color theory for painters is unscientific, and really about what paints mix well with other paints. Color is much more relative in painting as well.

Actually the primary pigments should be called magenta, cyan and yellow, not red, blue & yellow!. This is a misnomer that afflicts every K-12 art class and even colleges; indeed it's a complete cultural misunderstanding!

Try making all the colors with red, blue & yellow.. it's not possible.

Our eyes have three types of cones; sensitive to red, green and blue. To "modulate" their responses in a subtractive manner we have to use the opposite colors; cyan, magenta, yellow. Red, blue & yellow will create a very limited gamut of colors.

Artonpaper has the right idea; people say RBY, but they actually mean CMY, and this same problem can be seen throughout the history of 3-color photography. The people who understood this idea well, F.E. Ives for instance, were adamant about using the proper terms. Magenta, peacock blue, yellow.

So to answer you question David, painter's primaries and the photographer's subtractive primaries are (or should be) the same.

If you mix red and green light you get yellow.

If you mix red and green paint, you get disappointed.

Paint is a reflective medium, so the subtractive primaries (magenta, cyan and yellow) work best when one is trying to plot out how to combine colours.

holmburgers said:

Artonpaper has the right idea; people say RBY, but they actually mean CMY,

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That's funny--for as long as I've worked in publishing and done any kind of graphic arts work, I've always referred to four-color process as CMYK, and every printer I've ever worked with has done so, too.

I have always heard the standard 4 color press process referred to as CMYK, for cyan, magenta, yellow, and key, key being black ink.

http://en.wikipedia.org/wiki/CMYK_color_model

Lee

(close to a tie with Moopheus )

Well K is just there to make things easier. It plays no part in color synthesis per se.

C'mon guys... you're getting nit-picky...

Yes, primary colors are subjective! You can invent your own color system where you have, for example, red, orange and yellow as primary colors. The problem is, you get only a small fraction of colors visible to human eyes by mixing these colors.

They still teach in school that the "primary colors" are red, yellow and blue. It's nothing special, they are just 200 years out of date, just like much of the information taught in school. Well, they still teach that different areas of tongue taste different basic tastes, and there are four basic tastes. All this is 100-year-old information or complete disinformation to begin with.

Red-Yellow-Blue is a somewhat useful color model and used in traditional painting to some extent. However, most painters will add many more pigments than just mix these three. It's because you cannot achieve that many colors with just red, yellow and blue.

Today, it's a complete waste of time to teach some arbitrary, obsolete color space that was never used that much, as some kind of "default case", but they still do that.

But, to start with, you need to grasp the concept of additive and subtractive color synthesis. Additive uses RGB and subtractive CMY to get practically all of the colors visible to human. Any other system fails in creating that many colors, simply because of how the eye works. And painters use very complicated systems with dozens of pigments, not Red-Yellow-Blue.

So be it, holmberger, you just got me the confirmation I wanted: "So to answer you question David, painter's primaries and the photographer's subtractive primaries are (or should be) the same"

There really is something wrong here and your responses do confirm this disparity in different ways. Perhaps the problem is in the academia attached to this pragmatic matter. We should start with our 'cones' (that is what we are born with, after all). Then build upon that. But WHY does mixing, say, as Matt King says, red and green PAINT offer an entirely different color than mixing red and green LIGHT?

I guess what I am getting at here is just why are CMY so much more appropriate to call 'primaries' than are red, blue and green? What is it about those more 'solid' colors (RBG) that seem to stand in the way of being able to blend, whether with reflective media (paint) or translucent light? Being rather ignorant of extended color theory I must, nevertheless, state that there is something unyielding and solid and 'separated' about this RBG as opposed to the more pliable and blendable CMY. Am I making ANY sense here or am I doing what I do best, ie 'going off on a tangent'? - David Lyga

Photo enlargers have always used CMY filters. The confusion is coming from the digital age (and analog video for that matter) which use RGB sensors in the cameras and RGB-based processing for video projection. I think most, if not all, of the first mass-marketed color computer printers used RGB inks. All digital displays, AFAIK, are RGB.

If you want to have an idea of how "additive color" works then all you need to do is a little Photoshop. Start with a black background and make pure red, blue and green circles about 1/4 of the available workspace on three new separate layers. Change the Layer Mode to Screen on each circle layer. Now arrange them so that they all overlap a small amount in the middle. That middle patch will be pure white (B+G+R=W) and B+G=C, G+R=Y, and R+B=M. You can pretend that each of the circles is thrown from a flashlight with a filter over the front and you've overlapped the light beams.

There's not a very accurate way to display "subtractive color" in Photoshop but the following will give you an idea...
Add another layer just above your background and fill it with white. Change the Layer Modes on all colors to Multiply then decrease all three circle layers to 50% transparency. Now you can see how subtractive color works... more-or-less. The center patch is the darkest dark gray but if there was a Layer Mode to more accurately display subtractive color then it should be black. R+G=Brown, R+B=Purple, G+B=Teal.

You can do the same experiments with CMY.

ETA: The CMY overlaps will be RGB. Oh, and you'll have to change the opacity of the CMY "additive" circles to 50% and the CMY "subtractive" circle to 100%... just the reverse of the RBG settings.

Sometimes to illustrate (and to mentally picture the colors you will get) the subtractive colors are described by what they reflect and what they absorb (subtract).

-Cyan reflects two out of the three, Blue and Green, subtracts Red
-Yellow reflects Green and Red, subtracts Blue
-Magenta reflects Blue and Red, subtracts Green.

The pigments blend successfully because each on its own only takes away a third of the spectrum, so you have more flexibility.

Light is additive. Pigment is subtractive. Let's get out the Algebra for a minute. R=Red, G=Green, B=Blue, W=White, C=Cyan, M=Magenta, Y=Yellow.

In light (additive):
Given: R+G+B=W.
Given: R+G=Y
Given: G+B=C
Given: R+B=M

Using Algebra I, We can think of C, M, and Y as:
C=W-R
M=W-G
Y=W-B

You can think of Cyan as being "Minus Red", Magenta as being "Minus Green", and Yellow as being "Minus Blue." Mixing Yellow and Cyan together we know gets you green from experience. Algebraically, W-B-R=G, W-B-G=R, W-G-R=B.

Does this help, or did this engineer over-complicate things?

Old-N-Feeble said:

Photo enlargers have always used CMY filters.

Click to expand...

Not true. Although most color enlarger heads use subtractive filters Minolta/Beseler made the 45A additive color head. Phillips also made the PCS-150 and PCS-130 additive color enlargers. All were great color heads. The Phillips used potentiometers controlling the intensity of three lamps, each of which was completely filtered by sharp cutting red, blue, or green dichroic filters.

The use of additive primary color filters allowed one to print on only the cyan, magenta, or yellow layers of the color paper for printing negatives with the Phillips heads, something I've done myself. And because the filters were centered on the spectral sensitivity for the paper layers, only 35 watts max were needed per channel for efficient, short exposures.

Lee

Brush painters are taught that the primary palette colours are red, blue and yellow to mix subtractively into derivative colours. Many thousands of colours can be mixed from painting than in the RGB spectrum. No film on earth would come close to the delicate hues of e.g. the old Masters or Renaissance works, which look better the old they get.

I can recall that RGB is a carry-on from the cathode-ray tubes that emitted just three colours to form a picture. It's stuck with us for LCD screens and film — the latter in various intensities.

In traditional pre-press, CMYK are spot colours; I don't recall them ever been referred to as primaries in pre-press, but I guess the old school might have lazily termed it that.

Bill Burk said:

-Yellow reflects Green and Red, subtracts Blue

Click to expand...

I have seen yellow filters described as minus blue.


Steve.

Well first, take a look at a spectrum (like a rainbow) of the light to grasp that white light includes a multitude of colors.

David Lyga said:

But WHY does mixing, say, as Matt King says, red and green PAINT offer an entirely different color than mixing red and green LIGHT?

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Because the paints filter light; that is, they remove light. Although it's mixing, it's quite close to putting translucent layers (think of wratten filters) on top of each other. White light from the sun or artificial lamp shines through the red paint layer. The red paint layer lets red light go through, destroying every other color. Then, the resulting red light goes through the green paint. Because green paint would let only green light pass, and there is no green light left to pass, the result is black - all light has been destroyed, partly in red pigments, partly in green pigments. In practice, the paints are far from "perfect" red and "perfect" green, thus you don't get black but some kind of ugly brown; not all light is absorbed by these paints.

So, pure red paint could be called "remove everything from blue to yellow" paint.

By mixing more paints, you remove more colors.

This is simply because no pigment can create light. They don't shine in the dark. The only way they can work is by removing "unwanted" parts of spectrum.

If you mix more paints, you remove more colors. Pure, vivid red and green paints BOTH remove yellow, so you make double-sure you won't have yellow when you mix them.

So, paints that remove large sections of spectrum are not used that often: pure red, green or blue let only a small fraction of light pass, removing almost all other colors. So you don't need to mix them with anything else to remove anything more.

Instead, paints with broader spectral passband, for example, yellow are used. Yellow paint (usually) removes only blue, and lets everything from green through green-yellow, yellow, orange to red pass through. This creates you an opportunity to FURTHER remove colors by mixing in another paint.

As for your original question, it's only a terminology play. "Primary colors" are just some arbitrary colors that can be selected. Then, in that same system of your choice, the "secondary" colors are colors created by mixing any two of your "primary" colors.

There are two widely used systems: additive where you create light, and subtractive where you remove light. In the additive system, primary colors are RGB. In the subtractive system, primary colors are CMY.

They teach that painters use red, yellow and blue. This itself is a big lie. Well, they look a little bit like red, yellow and blue, but the red and blue are FAR from vivid red and blue. Especially the blue is much more like cyan. The "traditional" painting colors thus are somewhat close to CMY but not quite, so they just cannot produce pure colors. If they were really red, yellow and blue, you couldn't mix them practically at all.

Two of my enlargers work with sharp-cutting narrow-band RGB filters. There is nothing subjective
about this whatsoever. These are true primaries. However, for convenience, the actual control
panel is YMC, which makes it easier to relate to starting points on paper batches, densitometer readings, and similarity to conventional subtractive enlargers. All this is related to the basic physiology and physics of color. Back when they taught YRB as finger paint primaries, it was to kids eating Elmer's glue.

As you can see, there are a multitude of ways to look at this problem, and not every way will click for every person.

Since you said 'let's get back to cones', that's what I'll do. Our eyes have rods and cones; cones are for color, rods are b&w and used in low light.

For whatever reason, our eyes are capable of seeing a region of the electromagnetic spectrum from about 400-700nm; blue-violet to deep red. This is probably a very useful range if you live on this planet and live like we do, whereas some animals (gulls for instance) can see into the UV. So in this respect, the color theory problem is a uniquely human concern. Our color prints might not look like reproductions of reality to an alien with a different range of sensitivity. Likewise, an example of two-color photography might look like a perfect reproduction of reality to someone who is color blind (missing 1 channel of sensitivity).

But back to Earth... evolution has seen fit to give us this range, and it doesn't do so by making our eye continuously sensitive to every wavelength between 400-700nm, it achieves it in a way that's quite similar to color photography, with 3 sensitive elements that each have a sensitivity curve. Through varying proportions of these 3 sensitivities, we get the sensation of all colors. This is the Young-Helmholtz theory of color vision, and these "curves" were an intense area of interest to color photography researchers around the turn of the century. See A Handbook of Photography in Colours by Tallent, Bolas, Senior.

3 cones and 3 sensitivities, with peaks at 420–440nm (B), 534–545nm (G), and 564–580nm (R). Curious that they resemble our color separation filters, and also the senstivities of the 3 layers in a color film...

RGB are the primaries, CMY are the secondaries (or if you must, subtractive primaries).

Additive systems assume the use of 3 separate lights to modulate RGB. Subtractive systems only have 1 light to work with, and thus can only subtract from white light.

As Steve pointed out, CMY colors will "minus" one color as light passes through them. Whereas RGB colors will minus two. So any two colors from RGB will minus everything, making black. Whereas mixing two "minus-one" colors will make an intermediate color. An RGB set can never make a color print on paper (or transparency) because of the preceding fact, and no system has ever used this.

If we want to make red on a print, we need to overlap yellow & magenta, which will subtract blue and green, leaving red.

The difference between additive and subtractive can be summed up like this: are we trying to create black or create white? With additive systems, black is the default, and we add lights to create white. Subtractive processes default to white and we have to subtract from this to get black.

I hope this is clear and I haven't just further muddied the water...

What's really amazing is how close the human Red and Green cones are in spectral response.

It's a little late now, but I believe we could have gotten away with making the three primaries Blue, Green and Greenish-Yellow.

Yes it is very surprising that the so-called "red" cone has its sensitivity peak at yellow*, not red. I suppose that because the human vision is more complex than that, and because there is crosstalk between different color channels (different cone types), the purest colors can be achieved with primaries differing somewhat from what the peaks would be if there was only one type of cones present at a time. Yellow light, while it indeed peaks the red cone, also causes a significant signal in green cones at the same time. This simultaneous signal causes the yellow vision.

Remember, we are not seeking for maximally bright vision with minimum energy (or maximum efficiency); we just want a maximum number of different colors representable with minimum number of color components possible. If we were to design an energy-saving computer screen, we might want to select those cone peak wavelengths. We would get red output much higher with much less power, but we wouldn't be able to produce pure red, it would be orange.

In fact, this is clearly noticeable in the response level in practice; at a constant power, 660 nm light, while being very pure red, is quite inefficient (dark to human eye) compared to 600-620 orangish-red light which is bright. This was the key difference when "super bright" red LEDs and laser diodes were invented; it was not a power up.

Bill Burk said:

It's a little late now, but I believe we could have gotten away with making the three primaries Blue, Green and Greenish-Yellow.

Click to expand...

If you want to represent all visible colors with just three primaries, you have to choose them very closely right and there is no option. This has been proven numerous times experimentally and anyone can repeat that very easily. In fact, the current primaries widely used are not optimum. There were problems finding suitable green phosphor for CRT tubes, and the green which was selected is way too yellow. This is why you cannot see certain vivid bluish-green hues on a typical CRT TV or computer screen, but can see those in a cinema projection on a film.



*) And note, when I say yellow here, it means a single wavelength between red and green, a different thing that yellow in subtractive CMY where it is a wide-banded yellow, including red, yellow and green wavelengths.

Thanks SIWA for helping me to understand how colors are formed in Helsinki. Fooling, really, thank you for the good description and the dethroning of the 'major' difference between 'primary' and 'secondary'. It really devloves into semantics. And, the lack of purity was also worthy to bring into the equation: how versed in the scientific valuation of hues is the average high school art teacher?

But I do wish there was a 'standard' that both artists and projectionists could finally agree upon. Most, here, are saying that, essentially, there really is no difference between the two, only subjective evaluation.

And, holmberger, you confirm that there is a more solid aspect to the RGB as it removes not one but two colors. Thank you.

Seriously, I am not up to your collective sensitometric level but I did round out my limited knowledge here. - David Lyga