[argyllcms] Re: Understanding display profiles

  • From: "Hal V. Engel" <hvengel@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 20 Jul 2008 15:34:50 -0700

On Sunday 20 July 2008 02:04:18 pm Volker Sauer wrote:
> On So, 20 Jul 2008, "Hal V. Engel" <hvengel@xxxxxxxxxxx> wrote:
> > > Okay, understood.
> > > A little question: if I specify -t 6500, do I
> > > a) need to fiddle around with the display controls to bring the display
> > > to 6500?
> >
> > You can and this will result in the best overall calibration.  Some
> > monitors allow you to adjust a number of different things and the reason
> > to make these adjustments is to minimize how much adjustment is needed in
> > the LUT curves to achive your calibration targets.
> >
> > > b) will the calibration do that for me, when I load the calibration or
> > > profile with vcgt tag in to the LUT?
> >
> > It can see above.  Normally you woud adjust the monitor controls AND
> > create a vcgt LUT table to get teh best overall results.
>
> Okay, this means the best would result would be to set -t to the exakt
> value of the color temperature set up (like 6385), right?

I am not sure I understand.  If you want to use the devices native white point 
then tell dispcal to do that.  Otherwise select a specific white point and 
adjust the devices controls to get it as close as possible.

But you might want to consider specifying a white point target and using the 
monitor controls on the second (no LUT access) monitor to get it adjusted 
close to the target white point and white level that you will be using for the 
main monitor.  The devices will still be different but the most important 
things will be close.  On some system that only allow you to set one LUT it 
affects both monitors and on others it only affects the main monitor.  If it 
affects both make the monitor control adjustments to the secondary moitor 
after the LUT is loaded.

The monitors you are using have way more controls for adjusting this stuff 
than the vast majority of LCD displays including things like black level which 
almost no LCD has a control for.  It also has the ability to be set it to an 
sRGB mode and if the monitors do not match fairly well when in sRGB mode then 
I would consider them defective and I would expect the vendor to replace the 
defective unit.

>
> > > And as far as I understood until now, the only possibility is load the
> > > .cal-file or the vgct tag to the first monitor with dispwin (at least
> > > when I do my photo work)
> >
> > Just do it at startup.  Why would you only do this only at certain times?
>
> Because it would only calibrate the left display resulting in a
> significant difference of the background pictures which is annoying when
> doing normal office work.

There are lots of things you can do to mitigate ths.  Try those first.

>
> > Well sort of.  But GIMP can use the X11 _ICC_PROFILE atom and should be
> > able to find the correct profile without you having to specify it if the
> > X11 _ICC_PROFILE atoms are set.  The same is true for Firefox 3 if you
> > have color management setup.  But it is not true for ufraw and I don't
> > know about digikam.  Recent versions of ArgyllCMS should handle setting
> > up the X11 _ICC_PROFILE atoms and loading the LUT(s) at system startup. 
> > You can also use Oyranos oyranos-monitor and xcalib to do the same thing.
>
> Good to know, that gimp and firefox can use the system profile. I'll try
> to load it with dispwin -I.

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