Why 3D?

I happened to read co-worker Jeffrey Ventrella's page http://www.ventrella.com/Ideas/YawPitchRoll/yaw_pitch_roll.html and the "Why 3" part reminded me...

Since (most) humans are trichromats, we've settled on a 3-dimensional color space: RGB for emissive and CMY for reflective, although in school you learn the approximation "blue, red, yellow" as the "primary colors". Our color monitors use RGB (subpixel, phosphor) triads which roughly correspond to the light frequencies that (most) human eyes are sensitive to. Graphics programming is often an attempt to make sure the right R, G and B values are used for each pixel to approximate reality. We also generate other color spaces (HSL, HSB) when convenient, each with three parameters. This might indicate that colors are inherently 3D, as is space.

Of course, it's all just hacks upon hacks.

Light can come in any frequency, from (infra)red through (ultra)violet, and is typically a mix of many frequencies depending on the source. (Sunlight happens to be a pretty good mix, for example.) A pure blue light would trigger the blue-sensitive cones in our eyes. A pure yellow light trips both the green- and red-sensitive cones in our eyes and the image post-processing of our visual system tells us "yellow". A television display implements yellow based on this hack - it mixes red and green which our visual system interprets as yellow. To an alien with a different visual system, this wouldn't work. An alien with a specific yellow-sensitive cone would be baffled as to why we saw Big Bird as yellow on one of our televisions, since a pure yellow light and a mixture of red and green perceived as identical by a human would appear distinct to this alien.

And there are aliens among us!

Some humans are lacking some of the chromatins and hence are mono- or dichromats. Colloquially we call this "color blindness". Evidence suggests that some humans may even be tetrachromats. Research is ongoing. Perhaps this explains some people's choice of fashion?

It also turns out that most vertebrates are pentachromats! Early mammals lost three chromatins and so most mammals are dichromats (hence "dogs can't see color"); primates later re-evolved a third chromatin. This means birds have a much more complicated color sense than humans - 5 dimensions of color! And of course many other animals have ultraviolet and infrared perception ability as well.

So while space appears to be truly 3D (not counting time and rolled up mini dimensions, which are beyond our ability to perceive), 3D color spaces are merely a human convenience, and the basis of many hacks.