Re: Lab and visible colours
Re: Lab and visible colours
- Subject: Re: Lab and visible colours
- From: Graeme Gill <email@hidden>
- Date: Thu, 29 Jun 2006 11:36:35 +1000
Giordano Galli wrote:
I'm particularly interested in 3D plots of the 'human gamut'.
I found a few, whose meaning I'm not sure about and that don't
look like a potato to me:
- http://www.brucelindbloom.com/index.html?LabGamutDisplay.html
- Wiszecky & Stiles, 'Color Science', Second Edition: Fig. 1(3.3.9)
on page 166 and Fig. 2(3.3.9) on page 167.
One of the troubles is that it's hard to define the 'human gamut'.
For strictly reflective sources, it is reasonably easy, because
the reflected light energy is limited by that of the illuminant,
and the illuminant is generally chosen to be a reasonable
one (ie. Daylight, uniform spectrum, etc.).
For emissive sources, there are no such constraints,
the light energy can be any wavelength, and any intensity.
It's therefore theoretically possible to infinitely extend
the 'human gamut' in the purple direction, simply by
increasing the lighting intensity (at least until your
eyeballs burn out !)
Now because this would be pushing the edges of the
human vision model being used, things probably wouldn't
quite work in practice as the theory would predict,
but there is still a degree of arbitrariness in
how far the human gamut extends, depending on
what power constraints you set.
One of the interesting corollaries of this, is that
it is theoretically possible to extend the gamut of
a normal CRT or LCD display, by creating an unconventional
profile. Say your LCD display is capable of 200 cd/m^2.
If you could set the white point to be at (say) 100 cd/m^2,
_without_ also constraining the R, G & B levels to also
be halved, then you could (roughly) double your visible gamut.
One way of visualizing this "trick", is if you took
a normal display gamut, magnified it by a factor of 2,
(ie. so it's white point becomes a Y of 200 rather than 100),
and then sliced the top off it so that Y has a maximum value
of 100 again, then you can see that the region above the
conventional gamut is filled in.
[I haven't got around to trying this trick in practice yet,
to see how usable it is. It would help to have a nice bright LCD
display to try it on..].
Graeme Gill.
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