Saturday, August 30, 2014

Color names of the corners of the RGB cube

I've been spending a lot of time with the RGB cube lately and my biggest lesson has been that while it is mathematically very symmetrical between the primaries, it is not symmetrical subjectively (no, this is not a surprise to most of you).   The corners of the cube are key points when messing with it, and in order of increasing luminance (which is a confusing order and I use to emphasize don't get fooled by the geometric symmetry):
  • black (0, 0, 0) 
  • blue (0, 0, 1)
  • red (1, 0, 0)
  • magenta (1, 0, 1)
  • green (0, 1, 0)
  • cyan (0, 1, 1)
  • yellow (1, 1, 0)
  • white (1, 1, 1)
If we believe advocates of opponent process color theory (I am one of them and am in good company given DaVinci stated the opponent primaries were the right ones like it was not a matter of debate), the "true" primaries  are red, green, blue, yellow, black, white.   Your own experience with the names of the "mixed" corners gives some meat to that; which color name is more part of the human vocabulary:
  • cyan
  • magenta
  • yellow
 In fact look at them and try to quickly name them:
The xkcd survey shows that the subject population is more comfortable with the color association with the word "cyan" than it is with "magenta", as is shown from this figure from the survey:

I am impressed people know what "cyan" is; I don't think I would if I weren't in graphics.  I think "pink" is not a bad choice subjectively, but (255,128,128) is more of a classic pink (and note how far it is from the magenta vertex!).  Anthopologists have studied what are the "order" color is added to languages as the develop and an image on the excellent Wired article about Crayola's influence on color naming in the current world has this figure summarizing the anthro work:

There too cyan and magenta appear to be second-class RGB citizens.  Interesting also that yellow trumps blue, and that is consistent with the theory that the RG part of the vison system came first in evolution but I don't know enough to comment on that.

Bottom-line is do take advantage of the wonderfully simple math on the unit cube when using RGB, but always keep in the back of your mind that color as an experience is more complicated and less symmetrical.


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