[argyllcms] Re: Generated camera profile too bright

  • From: "Andreas F.X. Siegert" <lists@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 02 Apr 2012 09:09:51 +0200

on 02.04.2012 08:54 Graeme Gill said the following:
> Andreas F.X. Siegert wrote:
>> I use "colprof -v -q m -a m -b n"
>> Is there a way to influence the brightness?
> Yes there is, but you need to understand what you are asking of
> the system when you make a profile. The default ICC assumption
> is that you want the white of your test chart to be perfect white
> in the profile.
> If your test chart is exposed so that it is not at full brightness,
> then the profile will brighten everything up to make it so.
Hmm, the chart (or actually the histogram) looks properly exposed when I
take the test image.
If only the white patch where blown I would understand it, but not only
the white patch but also the next grey patch is completely (RGB) blown.

If I look at the RGB values of the white patch in the app before I switch to
linear to generate the test tiff, where should it be? How close to 100% or 255?

> You can modify the white point scaling using the -U parameter.
> Try a value > 1.0.
Thanks, I'll try to fiddle with that.


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