[argyllcms] Re: Perceptual Reference Media gamut and ColProf
- From: Roger Breton <graxx@xxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 02 Nov 2011 10:48:27 -0400
Graeme und Ignacio.
Isn't the PRMG "workflow" well laid out, in that the source profile cannot
be anything other than "sRGB v4 Preference..." that's on the www.color.org
site? And only the Perceptual intent can be used for the conversion?
Graeme, does Argyll already support the creation of v4 output profiles?
Best / Roger
P.S. When do you ever find the time to sleep zzzzzz?
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx]
On Behalf Of Graeme Gill
Sent: November-02-11 8:39 AM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Perceptual Reference Media gamut and ColProf
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...
Hi,
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>(availab
> le
> 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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