Re: [Lcms-user] [SPAM] Re: Bug in soft proofing?

[Wolthera <gri...@gm...>]

Hey,

So, the person who made that bugreport, David Revoy, has tried to use
the profile because the printing company requested it of him, with
terrible results:
https://www.davidrevoy.com/article747/the-english-book-printed-project-production-report-2#c0747-1890

So, what is going on here that even though the profile is borked,
indesign is showing a proper proof(perhaps due to using a different
table? Bizare that photoshop then acts weirdly...).

And that in turn affects users because they just cannot follow the
printing company's instructions faithfully: everything looks weird in
LCMS running software. Is there something we can do to smooth this
out?

Pepper and Carrot is CC-BY licensed, and David has all the files
available on his website, so there's plenty of material to test
against. The real question is what is going on and how to solve it.

On Sat, Oct 12, 2019 at 5:52 PM Boudewijn Rempt via Lcms-user
<lcm...@li...> wrote:
>
> Thanks for the answer! I guess the profile is just broken then :-)
>
> On zaterdag 12 oktober 2019 17:49:29 CEST Marti Maria wrote:
> > Hi, nice to hear from you.
> >
> >
> > Regarding the issue, I've checked the profile with photoshop and also got weird results, so chances are the a2b1 proof table is not correct in this profile.
> >
> >
> > Softproofing is performed in lcms by two steps. In first step the image is converted to the target colorspace using the settings the user wish, bpc rendering intent, etc. Once we have the image in the desired colorspace, we measure the lab values of the colors. To do so, we use relative colorimetric (i.e., no gamut remapping) in the reverse direction. This is encoded in the profile as the a2b1 table and is often called the "proofing" table. This is different from using the reverse table of perceptual a2b0, which "undoes" gamut mapping to display the image. So, tables may be diffeent on certain profiles.
> > This could explain the differences you see.
> >
> >
> > Regards
> > Marti
> >
> >
> >
> >
> >
> >
> > On 8 Oct 2019 11:42, Boudewijn Rempt via Lcms-user <lcm...@li...> wrote:
> >
> >
> > Hi,
> >
> >
> > We recently received this bug report: https://bugs.kde.org/show_bug.cgi?id=412604 "CGATS21_CRPC1.icc has a different rendering between softproofed and converted".
> >
> >
> > As its summary says, if you use the profile provided in the bug report for soft-proofing, the rendering is different than when you use it when converting to CMYK. Because GIMP and Scribus have the same behaviour, I'm wondering whether this could be a problem in LCMS?
> >
> >
>
>
> --
> Boudewijn Rempt | https://www.valdyas.org | https://www.krita.org_______________________________________________
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-- 
Wolthera