From: Phil Dutre Subject: Re: Cosmic Encounter, MtG, Zarcana, Nomic, Fluxx, Mao... Date: Wed, 29 Mar 2000 13:23:34 -0500 Newsgroups: rec.games.board,rec.games.abstract Summary: What is color? Geenius at Wrok wrote: > > On Wed, 29 Mar 2000, Phil Dutre wrote: > > > Geenius at Wrok wrote: > > > > > On Tue, 28 Mar 2000, Phil Dutre wrote: > > > > > > > Funny you bring up the color analogy! No matter what 3 base colors > > > > you pick, there are always colors that cannot be made using only > > > > the 3 base colors. > > > > > > Oh? Name one. I pick the additive colors red, green and blue. > > > > Certain shades of brown and purple, and yellow > > Colors are defined by how they tickle the color receptors in our eyes. > Those receptors are sensitive to red, green and blue light. If we can see > a color, it can be created as a combination of those three hues of light. Wrong. The color sensitivity curves of the human eye are not independent, and you just cannot treat them as an orthogonal basis in color space. The result of this that you need 'negative' colors to match some colors in color matching experiments. There is no such thing as 'negative' light, so it is not possible to match such a color with the three primaries that correspond to our color receptors. The CIE (Commision International D'Eclairage - or something like that) therefore defined a set of basis functions, XYZ, that will always result in positive coordinates for all visible colors. But XYZ are not visible colors themselves, they are only defined in terms of their color matching functions. XYZ color space has only positive coefficients, but there are no 'colors' that conform to X, Y and Z. If you transform XYZ to RGB color space, you end up with negative coefficients, which means there are colors you cannot create using those R, G and B primaries. > Any color that can't be made using those three primary colors is a color > we can't see. The difficulty of reproducing a color on a computer monitor > or on photosensitive film or paper is strictly a technological limitation. It's also a physical limitation. Take the color of a monochromatic laser at 520nm for instance. Unless this color is one of your primaries, you can NEVER create that color using three primaries. Since there are an infinite amount of colors like this, and you only have three primaries, there are always colors that you cannot create in an additive system with positive coefficients using only three primaries. ANY monitor ever built, now or in the future, using only 3 phosphor primaries, will NEVER be able to reproduce all visible colors. It's a physical limitation. Anyway, this is way off topic for this newsgroup, and I suggest to continue this by private e-mail if you want to know more. Phil -- ======================================================================= Philip Dutre Program of Computer Graphics Cornell University phil@graphics.cornell.edu http://www.graphics.cornell.edu/~phil/ =======================================================================