[argyllcms] Re: negative primaries

  • From: Pascal de Bruijn <pmjdebruijn@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 7 Jun 2010 00:17:03 +0200

On Sun, Jun 6, 2010 at 10:51 PM, Elle Stone <l.elle.stone@xxxxxxxxx> wrote:
> One of the issues Graeme mentions in “What’s wrong with the ICC
> profile format anyway ?" is the fact that ICC v2 specifications
> disallow negative tristimulus values.
> Recently I was comparing the gamut shape and size of several working
> space profiles with the gamut of raw-rendered tiffs of highly
> saturated flower images. I came to the same conclusion Ben Goren did
> in the argyllcms archive
> //www.freelists.org/post/argyllcms/Optimal-color-space-for-an-image,4,
> that none of the spaces smaller than ProPhotoRGB were big enough to
> hold even moderately saturated images.
> But really even ProPhoto isn't big enough for all images. The blue
> channel of one particular flower image while still in camera space had
> lots and lots of detail. After conversion to ProPhotoRGB, the details
> in the blue channel had turned to a solid black blob. Once I started
> looking, a lot of images turned out to have this problem of blue
> channel detail going to black upon conversion to ProPhoto. I wrote up
> my findings here:
> http://www.dustystones.com/2010/photo-essays/intro/open-source-digital-imaging-intro.html
> and here: 
> http://www.dustystones.com/2010/photo-essays/negative-primaries/negative-primaries.html.

I'm noticing you're using AHD demosaicing, which is not really good
for an EOS 400D (or Digital Rebel XT)...

I have some samples about this at my old UFRaw FAQ:


Recently Darktable has gotten green channel equilibration, so the
mazing artifacts are resolved with any algorithm, however I seem to
like VNG4 with a tad of unsharp mask better.

Pascal de Bruijn

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