[argyllcms] Re: Perceptual Reference Media gamut and ColProf
- From: Ignacio Ruiz de Conejo <ignacio.ruizdeconejo@xxxxxxxxx>
- To: "argyllcms@xxxxxxxxxxxxx" <argyllcms@xxxxxxxxxxxxx>
- Date: Thu, 3 Nov 2011 00:38:14 +1100
Not in complete agreement with you.
I think is a V2 profile, but I will check it, I may be wrong, thanks for the
hint.
Defining it as input is precisely what i want to do. That way i will not
compress the cyans, for instance, given that the inks I am using go far beyond
the sRGB cyan.
In other words, printing (0,255,255) and interpreting it as sRGB is delivering
40% of my cyan ink. But if I force it to be interpreted through the PRMG
profile, I would use 100% of the cyan.
Maybe -S is not the way to go, but now that I have explained what I want to
accomplish (do not restrict the input images to be interpreted as sRGB, but
expand its interpretation to use up all the ink gamut), how can we manage to do
it, without V4 support?
In the end, obviously, what I am looking for is the RGB to CMYK transform, but
without collapsing the colors between the ORMG and the ink gamut, as a normal
link of the V2 profiles would do.
Thanks a lot,
Ignacio
> 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>(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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