[argyllcms] Re: General calibration questions
- From: Andrés Vattuone <andres.vattuone@xxxxxxxxx>
- To: Kai-Uwe Behrmann <ku.b@xxxxxx>, ArgyllCMS <argyllcms@xxxxxxxxxxxxx>
- Date: Sat, 8 Oct 2011 01:55:30 -0300
Thanks for each and every answer, Kai-Uwe.
All my questionaire stems from the fact that, since there are no v4
profiling options in Linux, i was planning to create a profile under Windows
and export it to linux afterwards. Then I realised that the proflles not
only store icc information but also video card information to be uploaded.
It is therefore essential to know exactly which information it stores unless
I decide to stick to windows and proprietary sofware. Or else I should
abandon v4 profiling.
I am trying to transport calibration settings from one OS to another.
>The Apple developers docu has informations.
Trivial as it seems, I can't find the vcgt tag specification. I did find
some mails written by Marti and have infered from them that the vcgt tag
just stores three curves with 256 values each. Is that right?
>> 3) Do different loaders behave differently?
>
> Some fail, while others do not. The usual habit. But they do mostly they
job reliably.
>
The question was aimed at knowing if they load white point, brightness or
other settings to the video card, and what exactly loading means. In the end
the question would be: what is capable of being loaded to a graphic card?
Just curves, or also bounds, matrix transforms, etc? In other words, let's
say you can tell a video card to set a certain white point. Do you do this
by modifying curves?
>> 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.
I don't know what X upload means. Does it mean setting the profile as
default in the system without modifying anything in the video card?
> 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.
>
So in the end they effectively modify the video card luts through the
XFree86/Xorg api. Right?
> 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
>
Very interesting. Very technical for a lay person though. I'll try to read
and decipher as much as possible.
>> 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
>
I will try to it, indeed.
Regards,
Andrés
On Monday, 3 October 2011, Kai-Uwe Behrmann <ku.b@xxxxxx> wrote:
>> 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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