[argyllcms] Re: The different color temperatures: questions

-------- Original-Nachricht --------
> Datum: Wed, 15 Apr 2009 10:55:21 -0700
> Von: "Hal V. Engel" <hvengel@xxxxxxxxxxx>
> An: argyllcms@xxxxxxxxxxxxx
> Betreff: [argyllcms] Re: The different color temperatures: questions

> I have a Sunsung 245BW and I have played with the controls
> on it extensively while measuring what the controls actually
> do.  The RGB controls on this monitor have almost no affect
> on the white point of the monitor unless I set them to totally
> crazy settings and even then they only have a slight affect on
> the white point. I have also done some of the same testing on
> a few other Sansung LCD monitors with similar results. The RGB
> controls are much closer to gamma controls for each individual
> channel and primarily affect the gray and black color balance.

I have briefly investigated my XL20 in Custom mode too. My impression is that 
Contrast and the RGB Color Controls basically do adjust the gain of the three 
channels, however they only work as expected as long as I set them to values 
BELOW the factory default.

When I set them to larger values, then they seem to multiply the signal with a 
factor of > 1.0, but then clip at 1.0, which indeed results in a behavior as 
you described above, i.e. the WP does not change, but the mid-tones do.

[I think I had observed a similar behavior on other displays too, but I never 
did care explicitly.]

For my XL20 in Custom mode, the following manual adjustment procedure seems to 
work fine:

1. reset the color settings to factory defaults

2. select the color temperature preset closest to the target WP chromaticity 
(i.e. one of warm5, warm5,... cool6)

3. adjust the RGB gains to fine-tune the WP chromaticity, but only turn them 
DOWN, not up (i.e. one of the R,G,B gain controls can remain at the factory 
default (50 in my case), and the other two ones end up with smaller values)

4. adjust Brightness control to meet the luminance target

5. adjust Gamma control to meet the gamma target approximately

Iterate steps 3..5 if necessary (since for instance changing backlight 
brightness will slightly change the chromaties too)

[I don't see any need to fiddle with the Contrast, except possibly for dark 
luminance targets, blow the minimum brightness.]

Regards,
Gerhard

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