[argyllcms] Re: USB problems

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).

regards,

Milan Knizek
knizek (dot) confy (at) volny (dot) cz
http://www.milan-knizek.net - about linux and photography

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