[argyllcms] Re: sRGB/AdobeRGB98 vs Lab (was Verifying profile quality...)
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 23 Mar 2006 23:11:40 +1100
Milton Taylor wrote:
So where does that leave us? What does that gamut chart you just plotted
actually mean? That we can see virtually any emitted colour if it's
strong enough?
It means what you want it to mean. It's an "absolute" boundary,
the "absolutely widest range of colors we can see between 380
and 700 nm". The way it's been derived (setting Y = 100) also
shows a limitation of the CIE CMF model though, since it doesn't
encapsulate practical limits such as "too bright" (that information
is elsewhere.)
What happens if you redrew the gamut to also limit the maximum energy at
any hue to something like the maximum typical brightness of an LCD?
(Say 250 cd/m2) knowing full well that this would only happen in
practice if you did something like discussed below?
Not sure. You'd have to pick a white point brightness, and the gamut
would depend on the two numbers you've picked, making it a
non absolute boundary (and therefor disappointing to those who would
like to know what the "speed of light" is).
If you went with this approach, wouldn't the more extreme colours look
brighter than white?
They shouldn't if they are derived from a normal source gamut.
> Wouldn't that be perceptually rather confusing? Or
would this idea have to be used with some subtlety so that the
perceptual effect was preserved?
It stops working if you aren't adapted to the lower brightness white point.
As for the technicalities, there are two issues there...firstly as you
would probably know Windows doesn't use profiles for its own rendering,
only it's video LUTs, so you'd have to also fiddle with those too in
some similar fashion. This would have to mean that White=256,256,256
input, but output is 128,128,128. Other colours could possibly generate
individual channel output values > 128.
No, it would limit all colors, thereby defeating the effect. You would
need a video card that could support different video LUTs in different
window regions. I don't think these are very common (or the windowing
software doesn't support this either.)
Secondly, re the windows fullscreen thing, I'm not worried about that
because I'm assuming you'd be previewing full screen anyway, like in
Photoshop's full screen mode. Which also does use the profile to adjust
what you're seeing.
Right, so it might be possible to experiment with this idea in that manner.
Of course, in theory the same effect could be created with printed output
as well, but the viewing conditions are even harder to create. You'd
have to be in quite a dark room (as in a low reflective surface on
absolutely everything, including yourself), so that you didn't adapt to
something lighter than the artificially "dull" white point of the print,
and of course you have to be shielded from any direct light from the illuminant.
(sort of a "bright shaft of light only falling on the print" effect in a dark
room).
Graeme Gill.
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