[argyllcms] Re: CC Profiles In X Specification and dispwin

  • From: "Frédéric Crozat" <fred@xxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 12 Jan 2008 22:29:16 +0100

On Jan 12, 2008 9:50 PM, Leonard Evens <len@xxxxxxxxxxxxxxxxxxxxx> wrote:
> I clearly still don't understand some things, so please be patient with
> me.  Just what is the distinction between the calibration" and
> "profile".   I looked at my profile with iccdump, and it contains a
> whole lot of information with the last three tags being rTRC, gTRC, and
> bTRC.  I've been assuming these are loaded in the Xserver as look up
> tables.  I even tried to decipher the code in xcalib and other programs,
> so I think I understand how it is done.   Which part of the profile
> would be loaded with xicc?

xTRC tags are part of the calibration "section" of the color profile.
They are loaded into X server using dispwin (or xcalib). And they can
be computed using dispcal.

Those informations could be incorrectly reset by gnome-screensaver if
they were loaded after gnome-screensaver startup.

The other part of a profile is characterization (or profiling). The
idea is that color requested (from a file, an application) might not
be displayable on a calibrated monitor. So, an color engine will try,
based on characterization data (obtained with dispread, for instance)
to translate colors requested to color displayable (I'm not sure I'm
very clear but I'm sure people will correct me).

xicc purpose is just to store in a "standard" location the
characterization data of a profile, so color-aware applications (like
gimp, eog) will use those data without any additional user

> I thought calibration referred to changes made to the monitor using the
> monitor controls.  Is that wrong?

Yes but don't worry, I've only started to understand this some weeks ago ;)

You can check 
for a quite verbose schematic (I recommend reading
http://www.normankoren.com/color_management.html for a introduction of
color management).

> I am also still very confused about how an application like eog or gimp
> 2.4 is supposed to make use of this information.  For example, in the
> gimp preferences, I have several choices.  I can specify a display
> profile, but I don't understand whether or not I should be using it if I
> use xcalib.  Would the luts be used twice in that case?  I've been
> trying to resolve these issues by experimentation, but that hasn't yet
> been very helpful since the changes with different arrangements are not
> very large.

you must use xcalib (or dispwin) to "calibrate" your display. And
then, either specify manually the same color profile in gimp for the
characterization part or use xicc and gimp will use those data when
you choose "try to use system monitor profile".

Frederic Crozat

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