[argyllcms] Re: Custom Illuminant

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

QUOTE
============================================================================
> And the following for Perceptual:
> - Do a Relative conversion from ProPhoto to AdobeRGB (making sure the
colors
> 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
(tiffgamut).

> 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
-O"HP_Z3100_CANSONPHOTOHIGLOSS_ARGYLL_LG.icc"
"HP_Z3100_CANSONPHOTOHIGLOSS_ARGYLL"

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

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
for HP_Z3100_CANSONPHOTOHIGLOSS_ARGYLL_LG.icc

If you would like to see the images, profiles and wrl files they are here:
http://www.irelandupclose.com/customer/argyll/gamlimiting.zip

Thanks!

Robert









Other related posts: