[argyllcms] Re: Custom Illuminant

  • From: <robert@xxxxxxxxxxxxxxxxxx>
  • To: <argyllcms@xxxxxxxxxxxxx>
  • Date: Tue, 8 Jul 2014 10:59:24 +0100

> And the following for Perceptual:
> - Do a Relative conversion from ProPhoto to AdobeRGB (making sure the
> are more or less within the AdobeRGB space before the conversion to avoid
> too much clipping).
> - Do a Perceptual mapping from AdobeRGB to print.

Yes, that's one way. Another is to feed in a smaller gamut
as the source into colorpof/collink -g. The smaller
gamut could be from a colorspace (iccgamut) or from the images themselves

> What would be nice would be to be able to make the smaller intermediate
> working color space using tiffgamut/colprof (from a range of typical
> images), but I don't see how that could be done.

I don't see why you would want to use the 2 step process, when
a 1 step with a smaller source gamut specified is more efficient.
Hi Graeme,

Well, yes, of course I would much prefer to do a 1-step with a smaller gamut
but I wasn't able to generate the smaller-gamut profile.  I have tried to do
this using tiffgamut and colprof with -g, but the gamut appears identical
with or without the -g (viewing the icc profiles using viewgam and also
GamutVision from Imatest). The gamut volumes shown by GamutVision are a bit
different, but not much: with -g: 840629; without -g: 848999.

I assumed that the effect of the -g was not to reduce the size of the gamut,
but rather to improve the efficiency of the gamut mapping.

Perhaps I'm doing something wrong.  Here are the commands I used:

tiffgamut -v -w -pj -k -cmd -Omygam.gam t1.jpg t1.jpg t2.jpg t3.jpg

(All 3 JPGs have ProPhoto as the embedded profile. 

With -g:
colprof -v -A"HP" -M"Z3100" -D"HP_Z3100_CANSONPHOTOHIGLOSS_ARGYLL_LG" -qh
-cmd -dpe -SProPhoto.icm -gmygam.gam

Without -g:
colprof -v -A"HP" -M"Z3100" -D"HP_Z3100_CANSONPHOTOHIGLOSS_ARGYLL" -qh -cmd
-dpe -SProPhoto.icm -O"HP_Z3100_CANSONPHOTOHIGLOSS_ARGYLL.icc"

What is also interesting/puzzling is that mygam.gam is made from very
desaturated images, and yet its gamut is bigger in places than
HP_Z3100_CANSONPHOTOHIGLOSS_ARGYLL_LG.icc (iccgamut/viewgam).  The Photoshop
gamut warning does not show any of the three images as being out of gamut

If you would like to see the images, profiles and wrl files they are here:



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