[argyllcms] Re: Perceptual Reference Media gamut and ColProf

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 02 Nov 2011 23:38:43 +1100

Ignacio Ruiz-de-Conejo Viloria wrote:
> I am experimenting with Colprof (1.3.2) and so far had always used sRGB
> with the -S parameter to apply the gamut mapping.
> However, as an experiment, I told myself "why not using the ICC´s PRMG
> profile instead?" That way, instead of limiting the input to sRGB I can
> redefine the input gamut space to another, closer to that of the inks I am
> using...

        I suspect you are confused. The parameter to -S is the gamut
of the input images you want to gamut map. The "inks you are using"
are likely to be the output gamut you want the images mapped to,
and colprof knows what this gamut is, because it's that of the profile
that's being created.

> To my surprise, when I use the PRMG
> profile<http://www.color.org/profiles/PRMG_RGB-sRGB_based.icc>(available
> in
> color.org), Colprof breaks with the following message

I think you will find that that is a V4 profile. Argyll only works with
V2 profiles. V4+PRMG profiles work on a slightly different basis
to Argyll profiles when it comes the gamut mapping
(see <http://www.argyllcms.com/doc/iccgamutmapping.html>).
Even overlooking the V2/V4 incompatibility issue, it wouldn't
be possible to mix and match them without adding some sort of
V4+PRMG compatible gamut mapping mode, which would severely restrict
the choice of gamut mapping intents (ie. "perceptual" effectively
becomes "saturation").

> C:\color\PRMG_RGB-sRGB_based.icc: Not a TIFF file, bad magic number 0 (0x0).
> colprof: Error - Can't open file
> 'C:\WINDOWS\system32\spool\drivers\color\PRMG_RGB-sRGB_based.icc'*
> The same command line using the sRGB profile works fine.
> So, I must have misunderstood the usage of the PRMG profile.
> What is weird, though is the error message, is colprof trying to open it as
> if it were a TIF file (???)

The error message is not ideal (I'll see if I can suppress it better), but this
is a consequence of it accepting either an ICC profile or a TIFF file with an
embedded ICC profile as the source of the profile. The latter is useful for
tagged images, and removes the need to separately extract the ICC profile
from the image.

Graeme Gill.

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