Shining Color Space – Part 5: Color Theory

A short intermission: I want to omit the quirks of human color perception in order to give you a cartoon version of human color perception. We have three types of color sensitive cells ("rods") in the human eye: one for red, one for green and one for blue. This would roughly map to an three axis RGB color space (plus quirks). However there are better suited color spaces for understanding human color perception. An example is the L*a*b* color space, which is close to human perception of color. The three RGB axis have been transformed to the three L*a*b* axis: we have a light luminance axis or white-black axis ("L*"), a red-green axis ("a*") and a blue-yellow axis ("b*"). (See Natural Color System for a shorter example.)

In such a perceptive color space we can consider six distinct color points that could be constructed as defining "corners" of that perceptual color space. "Pure" white, pure red and pure blue, plus the "anti"-color points black, green and yellow. (BTW, white and black are sometimes not considered "colors", but are essential in defining color spaces.) All else colors are "mixtures" between those endpoints and exist on a continuum in a 3D space between those points – the ratio on each axis defines a color.


With regards to emissve colorspace: There are the three primary colors – pure red, pure green and pure blue – plus white (or rather the "white point", light of all colors mixed in a certain ratio) and black (no light). Again: Those last two are sometimes not considered "colors", but are essential in defining color spaces. All other colors (or rather color points in this 3D space) are mixtures and exists on a continuum, and the ratio between the three rods defines a color.

What I wrote about is the case for what the human eye can perceive: an emissive or additive color space. Objects like fire-engines and walls are typically not emissive, but reflective, and for those the subtractive color space applies. There we have also three primary colors, but these are now cyan, magenta and yellow! And furthermore these primary colors depend on the process creating them, as in the color pigments used!

The three additive primary colors are the "anti-colors" to the subtractive colors (and vice versa): E.g. cyan is a mixture of green and blue, but does not contain red, so cyan is "not-red". Red is not a part of the mixture for cyan, so red is "not-cyan". If you go and invert colors, the primary colors of one turn into the primary colors of the other. (Invert the colors in the opening titles of The Shining, and the title font becomes red. C.f. below the reason why surgeons wear cyan colors.)

See Natural Color System (NCS) and Opponent process:
"The NCS color model is based on the three pairs of elementary colors (white–black, green–red, and yellow–blue), as defined by color opponency."

(BTW, this is the reason surgeons wear cyan/green colored garment: First of all one can see any blood stains that weren't removed during cleaning. And secondly during an operation with its bright lights, exposure to one bright color desensitized the eye but but the eye stays sensitive to the "anti-color", and the problem with the red/bloody body gets mitigated.)

The three primary additive colors (pure red, green and blue) that the eye could perceive tend not to appear in nature in pure form, with the possible exception of blue in some parts of the blue sky and green for auroras. What we see in nature is always mixed, e.g. the green of the plants have a bit of red mixed in. Otherwise the pure primary additive colors can only be created by artificial light, e.g. a LED or a laser. Typically when people talk about primary colors, they mean something Fire-Red, which in fact is not a little bit away from the end point of the additive color space that the human eye can perceive, and is not a primary color in the subtractive color space. So what we consider "primary colors", like red, are actually not in the strict sense, but always mixtures. But we gloss over this and can call red, green, blue, cyan, magenta and yellow – those six more or less "pure" colors – "primary colors". Regardless of whether we are in emissive or reflective color space, these six "primary colors" hold special meaning, and it is some of those primary colors that play a dominant role in The Shining.