[argyllcms] Re: General calibration questions
- From: Kai-Uwe Behrmann <ku.b@xxxxxx>
- To: andres.vattuone@xxxxxxxxx
- Date: Mon, 3 Oct 2011 09:45:09 +0200 (MEST)
Date: Sun, 2 Oct 2011 20:42:21 -0300
From: =?ISO-8859-1?Q?Andr=E9s_Vattuone?= <andres.vattuone@xxxxxxxxx>
Hi, dear list members,
I would like to post some questions related to calibration. Any answer,
comment or link to further reading will be much appreciated.
1) Where can I find documentation about the vcgt tag?
The Apple developers docu has informations.
2)Are there any other tags related to calibration? Documentation?
Oyranos uses the meta tag:
http://oyranos-cms.blogspot.com/2010/10/icc-meta-tag-in-device-profiles.html
http://lists.freedesktop.org/archives/openicc/2010q4/002293.html
3) Do different loaders behave differently?
Some fail, while others do not. The usual habit. But they do mostly they
job reliably.
4) Appart from Gamma curves do they load anything else?
Some load these three curves only, some take over as well the ICC profile
to X upload. E.g. Oyranos uses xcalib, while GCM uses own code or gdk.
5) Are gamma, brightness, white point, contrast settings (or any other
settingts) from the monitor completely independent from those of the video
card?
These properties can be set in graphic cards LUTs.
You can observe these curves with ICC Examin:
http://www.oyranos.org/#icc_examin
6) Same question in the case of DDC compatible cards and monitors?
The same answere, but under Linux we have no API available to control such
capabilities. The ddcontrol project aimed at some point to such a API.
Unforunedly the project was not very active the last time I looked at it.
7) Depending on the answer of previous questions, may the loders be
capabable of loading all necessary calibration settings?
Would be really appreciated. Total control is hard due to the missing
DDC API. Vendors have added as well custom and proprietary controls, which
are hard to cover. One typical way is to instruct a user about manually
handling all needed setting for a given monitor ICC combination. An
other way is to just say, if unsure just recalibrate and reprofile.
For distributed profiles manufacturers typical provide ICC profiles, which
match defaults/factory settings.
8) Finally, I have little experience with Linux. I quote from Wikipedia
Use an LUT loader to actually load the LUT adjustments contained within
the profile
prepared during calibration. According to the documentation, these loaders
do not
modify the video card LUT by itself, but achieve the same type of
adjustment by
modifying the X server gamma ramp. Loaders are available for Linux
distributions that
use X.org or XFree86?the two most popular X servers on Linux. Other X
servers are
not guaranteed to work with the currently available loaders. There are two
LUT
loaders available for Linux:
Xcalib is one such loader, and although it is a command-line utility, it
is quite easy
to use.
dispwin is a part of Argyll CMS.
The sentence "these loaders do not modify the video card LUT by itself, but
achieve the same type of adjustment by modifying the X server gamma ramp" is
unintelligible to me.
The "X server gamma ramp" points to the XFree86/Xorg APIs. The other way
would be to talk to the graphic card driver, which is barely used if at
all.
kind regards
Kai-Uwe Behrmann
--
developing for colour management
www.behrmann.name + www.oyranos.org
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