[argyllcms] General calibration questions
- From: Andrés Vattuone <andres.vattuone@xxxxxxxxx>
- To: Kai-Uwe Behrmann <ku.b@xxxxxx>
- Date: Sun, 16 Oct 2011 02:44:57 -0300
Hi dear list members,
Thanks Graeme Gill and Kai-Uwe Behrmann for your replies.
Graeme Gill wrote:
>> 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).
For the time being, I am interested in display calibration, the unavoidable
starting point for color management. I would like to know more about printer
calibration but I'd rather go step by step.
Kai-Uwe Behrmann wrote:
> >The Apple developers docu has informations.
>
See:
http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/ColorSync_Manager/Reference/reference.html#//apple_ref/doc/constant_group/Video_Card_Gamma_Tags
As far as I can understand, the vcgt tag offers two alternatives, either
storing gamma values for each channel (I don't know what the min and max
gamma means) or else store a function as a table for each channel,
eventually the same for all. My very limited knowledege of programming
language doesn't help me to grasp the bit depth of this table or how it is
encoded.
Graeme Gill wrote:
>> 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".
I think I already understand the diffrerence between tweaking calibration
and setting a default profile either at the OS level or the application
level.
What does exactly Argyll do as regards calibration? I presume it reads
either gama values or else 1Dlut curves and saves it on some type of memory.
(The cards memory?)
I tried another loader and they gave the same results. I tested this with
Argyll, reading a series of test patches.
For some unknown reason I wasn't able to load the vcgt tag directly from
profiles using Argyll yet. I have to check the documentation again. So I
implemented the following workaround in Windows: I installed the profile as
default, extracted with Argyll the calibration information to a calibration
file and finally loaded the calibration settings with Argyll.
Graeme Gill wrote:
>> 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.
I am trying to prevent any unwanted calibration changes either by the
monitor, the video card or the OS. Or at least be informed when such
changes occur. For instance, I want to mantain the state of calibration
when I restart the OS, or change from Windows to Linux. This may involve
loading vcgt, eventually keeping other video card settings not included in
the vcgt tag (maybe they are in other tags which some loader could read),
keeping monitor settings and, in the case of DDC comoatible hardware,
knowing if some calibration setting is being passed on, or preventing
communication alltogether.
So I am try to learn all possible ways in which calibration can be altered.
Video card luts are stored in the card's memory?
The settings that the drivers presumably implement by manipulating their
luts are stored in the luts themselves? Or perhaps elsewhere, some place the
loaders can't access? What if they had 3d tables? Are the 1Dluts stored in
the vcgt tag loaded there?
If you have DDC compatible hardware are the physical controls on the monitor
still independent from the video card?
Kind regards,
Andrés Vattuone
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