Re: [Gimp-developer] Documentation on color spaces

Elle Stone (l elle stone gmail com) wrote:
On 10/9/13, Simon Budig <simon budig de> wrote:
Another (slightly philosophical) issue for me is, that you never explain
what you mean by color.

I added a one-paragraph summary of color:
What do you think? Will my one-paragraph summary work?

Yeah, I like it.

I am not sure if mentioning this helps or if it confuses stuff...  :)
Based on your input I rewrote the explanation of imaginary colors,
hopefully clarified what a "real" color really is, and touched on the
subject of nonstandard color perception. Metamerism, though very
important, might be more distracting than helpful?

Yeah, Metamerism probably is distracting.

For my mental model of color the spectral distribution of the light is
quite important and I wonder if it would help a color-newbie to have
more of this "tangible" stuff in the text. But this certainly also is a
question of personal preference and I don't want to impress my views
onto your text  :)

To look at the weaknesses/hypothetical problems of the XYZ model there
are two things worth noting:

a) two distinct spectral distributions might end up at the same XYZ
b) there are XYZ coordinates in the first octant, which can not be
   mapped back to a spectral distribution.

(put in mathematical terms: XYZ is neither injective nor surjective)

And I'd explain it by looking at the monochromatic light (visible to the
"average human"), which has a very specific position at the border of the

By adding up more wavelengths you'll always end up inside the horseshoe,
(and there is more than one way to add up monochromatic light to end up
at a certain XYZ coordinate). On the other hand, creating an actual light
source with XYZ coordinates *outside* the horseshoe is an impossibility,
even for rocket scientists, unless we assign XYZ coordinates for
invisible wavelengths or allow for "negative" light sources...

The human aspect of XYZ is visible in two aspects: first the limited
spectrum we consider and then the weird shape of the horseshoe, which is
determined by the response curves of the "average" cones in the human
eye. But only the first one has an effect on the "reality" vs.
"imaginarity" of a XYZ coordinate IMHO.

However, adding tons of more diagrams with spectral distributions,
X/Y/Z response curves etc. would at some point destroy your intentions
with your text, so I won't complain...  :)

              simon budig de    

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