[argyllcms] Re: Generated camera profile too bright

  • From: "Andreas F.X. Siegert" <lists@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 03 Apr 2012 21:43:16 +0200

Thanks Elle for the analysis,

> http://ninedegreesbelow.com/temp/axf9375-nef.html
> The problem seems to be that your target shot is almost a full stop
> underexposed

With the stock profile I get 75% luminance in the white spot., yes, I
got confused y what I had seen in the cam histogram, there where somne
bright spots in the BG I assume.

Anyway, that is not necessarily a profile I want to use. I want to
understand how to create decent profiles for AS.

> Or you could apply about a full stop's worth of positive exposure
> compensation during raw processing of your target shot and reprofile.
> Or reshoot the target so it doesn't need so much positive exposure
> compensation.

There is no way to generate an image that will be bright enough after
the switch to linear. The drop is just too radical.

I just re-shot the target to be as close as possible to a fully exposed
white patch.
After switching to linear in AS the image is severely underexposed. I
need to bump it by about 2.8 stops to get back to the same exposure.
But using this then as the input for the calibration process will result
in a profile that leads to images that are at least a stop underexposed.

With a bit of trial and error, I generated a profile from a linear image
that was bumped up by 1.8 stops that led to a profile that then produced
a similar luminance on the white spot as the original image with the
stock profile.

I am currently on a crappy laptop screen so I really can't judge colors
but the first impression is sort of ok.



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