[argyllcms] Re: General calibration questions
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 11 Oct 2011 11:54:44 +1100
Andrés Vattuone wrote:
Hi,
> 1) Where can I find documentation about the vcgt tag?
It's an Apple tag, and there was some info on their website.
I'm not sure if it is still there, or exactly where it is
(Apple seem to aggressively delete old information.)
It was introduced in ColorSync 2.5 if that is of any help.
> 2)Are there any other tags related to calibration? Documentation?
Exactly what type of calibration in what context ?
(Note that Argyll supports printer and scanner calibration curves as well
as display video Lut calibration).
> 3) Do different loaders behave differently?
I've no idea. You might have to compare them yourself.
> 4) Appart from Gamma curves do they load anything else?
I can't speak for other loaders, you'll have to investigate
yourself, or ask the question of their authors.
Argyll's dispwin loads the vcgt values, but may also set
the operating system "current ICC profile".
> 5) Are gamma, brightness, white point, contrast settings (or any other
> settingts) from the monitor completely independent from those of the video
> card?
What settings in what context ?
Note that some graphics card drivers have such settings, that they
(presumably) implement by manipulating their lookup curves.
The physical display controls are independent of the display card.
> 6) Same question in the case of DDC compatible cards and monitors?
Since DDC is a communication between the display card and the monitor,
your question doesn't seem to make any sense. DDC connects the two.
> 7) Depending on the answer of previous questions, may the loders be
> capabable of loading all necessary calibration settings?
In theory they could, but there would be some proprietary
storage format to hold the display settings and associate them
with the calibration. This could take the shape of proprietary
ICC tags, or it could be something independent.
> 8) Finally, I have little experience with Linux. I quote from Wikipedia
> 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 _is_ the video card LUT, so the statement is nonsense.
dispwin will use the XRANDR access to the video card LUTs, if it is available.
Graeme Gill.
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