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 It's nothing special, they are just 200 years out of date, just like much of the information taught in school.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
Last edited by David Lyga; 04-12-2012 at 04:16 PM. Click to view previous post history.
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.
Last edited by Old-N-Feeble; 04-12-2012 at 04:51 PM. Click to view previous post history.
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.
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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):
Using Algebra I, We can think of C, M, and Y as:
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?
Shoot more film.
There are eight ways to put a slide into a projector tray. Seven of them are wrong.
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.
Originally Posted by Old-N-Feeble
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.
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.
I have seen yellow filters described as minus blue.
Originally Posted by Bill Burk
"People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.
Well first, take a look at a spectrum (like a rainbow) of the light to grasp that white light includes a multitude of colors.
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.
Originally Posted by David Lyga
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.
Last edited by hrst; 04-13-2012 at 07:28 AM. Click to view previous post history.