[argyllcms] Re: Generated camera profile too bright

  • From: Elle Stone <l.elle.stone@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 3 Apr 2012 11:54:16 -0400

> Looking at the NEF (raw) file in Nikon Capture NX2 at default settings, I am
> seeing the black patch at rgb 27, 27, 28 and the white at rgb 223, 225, 224.
> (The working RGB space is Beta RGB). So the exposure seems reasonable to me;
> it is the conversion to linear TIFF that is causing the big drop in
> lightness.
>

Linear output looks dark when there is not a proper linear gamma
profile embedded, because imaging software assumes sRGB (with sRGB
somewhat greater than gamma 2.2 overall gamma) when there is no
embedded profile.

I honestly don't know what Nikon Capture NX2 default settings are, but
I rather suspect they cater to NEF files and "by default" do what
needs to be done to make the processed raw file look good.

But using UFRaw with actual linear output, that target shot  needs
almost a full stop of additional exposure to get the white patch RGB
values above 200.

And according to the NEF metadata, the raw target shot was given -2/3
exposure compensation. ExifTool shows: Exposure Compensation
: -2/3

When making a profile from a target shot, it doesn't really matter
what the RGB readings are after conversion to BetaRGB or other working
space as performed by Capture NX2. What matters is the "raw color"
(after raw processing, but before converting to a working space) RGB
values.

Elle

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