[argyllcms] Re: How do I force dispcal to always map R0 B0 G0 -> R0 B0 G0 on the calibrated video LUT?

  • From: Alexander <adfirestone@xxxxxxxxx>
  • To: argyllcms <argyllcms@xxxxxxxxxxxxx>
  • Date: Sun, 20 Dec 2009 19:15:00 -0800

>  Reading though the manual it seems like it may have something to do
>> with the -f or -k parameters but the descriptions confuse me a bit.
> -f determines the type of gamma curve model used. -k determines
> how much the black is corrected to have the same color as the white
> point. Setting -k 0 will usually give a darker black, since it
> turns off this correction.
About the -f parameter, what would be usage scenarios to use -f 1.0 or
something like -f 0.5 instead of -f 0. How could I make an educated decision
on the -f value?

>  changes my 0.00cdm2 black into a ~0.05-0.10cdm2 black. When I set my
>> CRT to a very very dark black for night viewing, I want to keep that
>> very very dark black after calibration.
> The device value for black is determined by a heuristic. It's difficult
> to estimate given that many devices can have a "dead" zone near
> black, which we want to avoid so as to give a progressive response
> from black, and not loose the shadows. Maybe this heuristic
> could be changed, if it is not always doing the right thing.
> (I'm a bit reluctant to add yet another parameter, since this
> adds to confusion - see -f and -k above).
> Graeme Gill.
> I tried -k 0 and the result was near identical to -k 1. -k 0 actually gave
me a slightly brighter black then -k 1 on my quick test, heh...

I believe this may come back to the Eye-One Pro's weakness with
differentiating between very close together dark measurements. Along with
the issue of the Eye-One Pro detecting 0.00cdm2 as 0.05cmd2 randomly on my
CRT. The Eye-One is probably telling Argyll there is a dead zone, even
though I can see with my eyes that there is not. When I am in a dark room
that is obviously inaccurate since the screen is bright grey instead of

If would be nice if you could add some sort of override for heuristic, since
it does sounds like it would prove useful for my situation.

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