[argyllcms] Re: calibration vs profiling
- From: Adrian Mariano <adrian@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 27 Jun 2008 09:16:50 -0400
Milan Knížek wrote:
Adrian Mariano píše v Čt 26. 06. 2008 v 08:26 -0400:
I realized as I was looking over the "typical usage scenarios" that I
don't understand the difference between calibrating the display and
profiling the display. I've calibrated and I have a .cal file that I
can install with dispwin (which makes a very definite shift in the
colors when I install it). How does profiling differ?
Calibration puts the display to a defined state using some key
measures like gamma, white point, brightness. Technically, the
calibration is achieved by a combination of hardware manipulation of
the monitor (the knobs on it) and adjustment to the LUT table with the
Cal file (or VCGT tag of the profile - a profile normally does not
include calibration data, but for monitors it is more convenient then
having two separate files).
Profiling creates a profile, which describes how the calibrated
monitor displays colours (and how many of them). Then, the CMS-aware
application knows how to display colours so that you see them
correctly. Applications that are not CMS aware just display the
colours as they are without any conversion and the profile is useless.
You could probably skip the calibration step and use only a profile to
see correct colours (with apps that support CMS), too.
However, calibrating helps to get better colours also with
non-CMS-aware applications and has some other advantages. Majority
pictures on the internet expect that sRGB device will be used to
display them. sRGB has gamma close to 2.2 and white point 6500 K,
hence if you calibrate the monitor with these settings, you are close
to the expected displaying device at least with some basic parameters.
That means that pure white should look almost the same on various
monitors that have been calibrated to the same values. The same with
brightness/darkness of colours and possibly grey-scale.
On the other hand, a red colour can still look differently on
different monitors - this is where the profile comes in (with the help
of CMS-aware application). The CMS engine also takes care about
colours, which are not displayable on the particular monitor
(especially those saturated ones).
So if I don't have any CMS aware applications, and I just want to load a
monitor calibration at boot time into X then profiling won't do any good
for me? (X isn't CMS aware, is it?)
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