Great to see you are back with the Not so Stupid Question series. This makes a lot of sense; especially about light-emitting science and the benefit of using additive vs. Cheers Iris! I've often had a discussion um, argument with the wife about what are the primary colours- she comes at it from an art point of view and thinks RYB, whereas I come at it from a photography viewpoint and think of it as RGB.
Your eyes have detectors in for RGB which is why monitors and those multi-colour LED's all emit the same three colours. Paint works by only reflecting the relevant colour and absorbing all others which is why if you mix two colours, you're absorbing even more colour than one, and it' subtractive. Yellow light can be made up of red and green light- so your monitor showing yellow will have loads of red and green dots illuminated. Yellow paint is absorbing all colours apart from the light that the red and green sensitive parts of your eyes pick up though, and when you then stir in blue paint which absorbs red, and everything else apart from blue you're left with just the green sensor in your eye detecting light.
So, what gives? The reason for the confusing contradiction is that there are two different color theories — for "material colors" like the ones used by painters and for colored light. These two theories are known as additive and subtractive color systems. Stephen Westland, Professor of Colour Science at the University of Leeds in England breaks things down into simple terms before getting into the confusing complexities , in an email.
This leads to two types of colour mixing, additive and subtractive. Those are roughly sensitive to red, green and blue light. The additive primaries do this very directly by controlling the amounts of red, green and blue light that we see and therefore almost directly map to the visual responses.
The subtractive primaries also modulate red, green and blue light, but a little less directly. Let's get into those distinctions — but fair warning: everything you know about primary colors is about to change before your eyes. Let's talk about the additive system first. When he was 23 years old, Isaac Newton made a revolutionary discovery: By using prisms and mirrors, he could combine the red, green and blue RGB regions of a reflected rainbow to create white light. Newton deemed those three colors the "primary" colors since they were the basic ingredients needed to create clear, white light.
The shared intersection of two flashlight circles is brighter than either of the circles, and the third flashlight circle intersection will be brighter still. With each mix, we add lightness, therefore we call this kind of mixture additive light. The red and blue mix is lighter too, a beautiful magenta. And the red and green also make a lighter color — and a surprise to nearly everyone who sees it — yellow!
So red, green and blue are additive primaries because they can make all other colors, even yellow. When mixed together, red, green and blue lights make white light. Your computer screen and TV work this way. And if you've been onstage, you might have looked up behind the curtain to see the red, green and blue lights that serve as theatre's additive primary colors.
Most sources will tell you red, green and blue are the additive primaries, as Newton originally proposed, but Westland says it's a lot more complicated than that. Enter subtractive color. Take a piece of white paper; this paper reflects all of the wavelengths in the visible spectrum to a very high degree. Now add a yellow ink on top of the paper. The yellow ink absorbs the blue wavelengths, leaving the others — which are seen as yellow — to be reflected.
So rather than being additive, in this case we start with white all the wavelengths being reflected and then start to subtract light at certain wavelengths as we add the primaries. So the distinction in color systems really comes down to the chemical makeup of the objects involved and how they reflect light. For a subtractive color system, a certain reflected color is obtained by absorbing the opposite color. Therefore, the primary colors of the most effective subtractive system are the opposites of red, green, and blue, which happen to be cyan, magenta, and yellow CMY.
This is why most printed images contain a grid of little cyan, magenta, and yellow dots of ink. Cyan is the opposite of red and is halfway between green and blue. Magenta is the opposite of green and is halfway between blue and red, and yellow is the opposite of blue and is halfway between red and green. In summary, the most effective color systems are red-green-blue for additive color systems and cyan-magenta-yellow for subtractive color systems.
So where did the red-yellow-blue color system come from that they teach in elementary school? Typically, students first encounter color concepts when painting in an art class in grade school.
Paint is a subtractive color system, and therefore the most effective primary colors for painting are cyan, magenta, and yellow. Note that high-quality paintings typically do not use just three primary colors since more vivid scenes can be achieved using dozens of primary colors. But when teaching art, it's easier to start more simply; with just three primary colors.
Now, to a little grade-schooler, the words "cyan" and "magenta" don't mean much. Furthermore, to an undiscerning youngster's eye, cyan looks awfully close to blue and magenta looks awfully close to red.
Therefore, cyan-magneta-yellow becomes corrupted to blue-red-yellow. Elementary art teachers either ignorantly perpetuate this less effective color model because that's how they were taught as children , or intentionally perpetuate it because it's just too hard to teach six-year-old's the difference between cyan and blue. We discuss the opportunities offered by this model, potential obstacles, and related countermeasures, as well as future perspectives for its utilization.
The paper shows also examples of using the model for the evaluation of real methods.
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