[argyllcms] Re: Can anyone help with a weird OSX problem?
- From: Ivan Tsyba <ivantsyba@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 25 Jul 2014 11:46:24 +0300
My question is off topic.
What is ICC L*a*b*?
25 лип. 2014 11:05, користувач "Graeme Gill" <graeme@xxxxxxxxxxxxx> написав:
> Quartz wrote:
> >> This
> >> caused some smaller (matrix / shaper?) profiles to map saturated blues
> >> to more purple tints on the screen.
>
> Hi,
>
> to be technically correct, matrix profiles don't do any
> gamut mapping, and any clipping is done by the CMM
> and is likely to be simplistic, per component clipping.
>
> > So I've been doing more research on this. I notice that dispcalGUI has
> the following
> > option: "Normally, profiles created by dispcalGUI only incorporate the
> colorimetric
> > rendering intent, which means colors outside the display's gamut will be
> clipped to the
> > next in-gamut color.
>
> Note that cLUT type profiles will at least clip to the perceptually
> closest in-gamut
> color.
>
> > LUT-type profiles can also have gamut mapping by implementing
> > perceptual and/or saturation rendering intents." (I'm not exactly sure
> what this is doing
> > under the hood, or what options dispcalGUI is passing to argyll).
>
> It will be passing the -s or -S option to colprof.
> Note that some displays have primaries that lie outside the ICC L*a*b*
> range, so an XYZ based cLUT profile is required if mapping or clipping
> is to operate correctly.
>
> > The blue primary on my MacBook Pro display lies outside sRGB as best I
> can tell (it's kind
> > of off to the side, but I'm not exactly sure how to read these graphs
> yet so I'm not sure
> > if saying it's 'purple' is necessarily correct).
>
> Two explanations have been suggested to me for "blue goes purple" type
> problems.
>
> One is the use of "wrong Von-Kries" chromatic adaptation in adapting white
> points between D65 and D50.
>
> The other is gamut mapping or clipping in L*a*b* space, since perceptually
> constant hue lines have quite a curve on them near blue.
>
> > Would using a large LUT profile and enabling perceptual intent possibly
> solve or help
> > address my blue-turns-purple issue?
>
> It may, but be warned than some systems/programs expect display profiles
> to be
> matrix based, and choke on cLUT profiles.
>
> Graeme Gill.
>
>
>
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