[argyllcms] Re: Profile input white not mapping to output white

  • From: greg_soravilla@xxxxxxxxx
  • To: "argyllcms@xxxxxxxxxxxxx" <argyllcms@xxxxxxxxxxxxx>
  • Date: Thu, 22 Nov 2012 16:48:26 -0500

Maybe someone has better advice, but after correcting the RGB mapping (i.e. 
color correcting) the camera's sensor then maxxed sensor values generally would 
not map to "white" by nature.  So, I would recommend you NOT clip the photo, 
then correct it (so white is accurate), then clip it / overexpose it in 
Photoshop.

Greg

On Nov 22, 2012, at 3:31 PM, Ben Goren <ben@xxxxxxxxxxxxxxxx> wrote:

> First, happy Thanksgiving to all!
> 
> I'm photographing some artwork against a white seamless background, and 
> intentionally overexposing the background to force it to pure white, while 
> keeping the artwork within the exposure range of the camera. I'm shooting a 
> target in the scene, linearly processing it with RAW Developer (after setting 
> white balance, of course), and then doing the standard crop / chartread / 
> colprof / etc. to create a profile.
> 
> Here's a thumbnail of the overall scene (with linear development):
> 
> 
> <706C8559.jpg>
> 
> 
> 
> Here's the image after applying the profile (created with no options given to 
> colprof):
> 
> 
> <706C8559-profiled.jpg>
> 
> 
> Except for the pale green background, I'm happy with the results.
> 
> If I use -u, the background remains less than pure white, but the tint is 
> very much reduced (though the lightness remains about the same). I can mask 
> it out reasonably enough in Photoshop, but that's obviously undesirable.
> 
> If I create a profile with -ag, the background is pure white, but both by the 
> numbers and by eyeballing it the quality is much diminished. If I use -as, 
> the results are somewhere between the two, both in terms of a not-white 
> background and quality otherwise. With -ax, the numbers are marginally closer 
> but there's severe posterization.
> 
> I'm attaching a Zip file with what I hope are enough relevant files to 
> reproduce what I'm doing, less the 27 Mbyte RAW file. I can, of course, 
> supply that as well. In its place, I'm including a 50% scaled JPEG at 50 
> quality, which I hope should be "good enough."
> 
> Any and all help would be much appreciated.
> 
> Thanks!
> 
> b&
> 
> <help.zip>

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