lcms-user

[Lcms-user] Bug in soft proofing?

[Boudewijn R. <bo...@va...>]

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

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

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

I wanted to add to this that I previously did mail about this issue in
Krita, but then Real Life happened, and I was unable to answer. So I
am going to outline the color management er... 'pipeline' within
Krita(Cannot speak for GIMP and Scribus).

Say we have a situation where we have an Image profile, a CMYK profile
and a Display profile. When we're using conversion (which gives the
correct result), we're going from

Image profile -> Display Profile

Where the rendering intent and blackpoint compensation is configurable
by the user. The user then converts, where they too can configure the
rendering intent and BPC, leading to.

Image Profile -> CMYK Profile.
CMYK Profile(The new image profile) -> Display Profile.

Now for softproofing, we have the following:

Image Profile -> CMYK Profile -> Display Profile.

The rendering intent and bpc is the same for both transforms(and
configured by the user), which may not be strictly correct. However,
even when we set up the configuration so that the conversion pipeline
and the softproofing pipeline use the exact same configuration, the
softproofing result looks faded compared to the conversion result.

I hope this helps figuring out what is going on.

-- 
Wolthera

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

[Marti M. <mar...@li...>]

<div dir='auto'><div>Hi, nice to hear from you.</div><div dir="auto"><br></div><div dir="auto">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.</div><div dir="auto"><br></div><div dir="auto">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.&nbsp;</div><div dir="auto">This could explain the differences you see.</div><div dir="auto"><br></div><div dir="auto">Regards</div><div dir="auto">Marti</div><div dir="auto"><br></div><div dir="auto"><br><div class="gmail_extra" dir="auto"><br><div class="gmail_quote">On 8 Oct 2019 11:42, Boudewijn Rempt via Lcms-user &lt;lcm...@li...&gt; wrote:<br type="attribution"><blockquote class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">Hi,
<br>

<br>
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".
<br>

<br>
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?
<br>
-- 
<br>
Boudewijn Rempt | https://www.valdyas.org | https://www.krita.org</p>
<p dir="ltr">_______________________________________________
<br>
Lcms-user mailing list
<br>
Lcm...@li...
<br>
https://lists.sourceforge.net/lists/listinfo/lcms-user
<br>
</p>
</blockquote></div><br></div></div></div>

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

[Boudewijn R. <bo...@va...>]

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

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_______________________________________________
> Lcms-user mailing list
> Lcm...@li...
> https://lists.sourceforge.net/lists/listinfo/lcms-user



-- 
Wolthera

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

[<Mar...@li...>]

Quoting 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...).

In the thread you mention, there are other people that found the  
profile to be buggy in photoshop. So, I have further investigated this  
profile, and found the source of problems on the B2A1 table, that is,  
the relative colorimetric proofing direction. It is broken. It seems  
to me that it is implementing some sort of absolute colorimetric,  
which would be emulating the paper white. Some products of Adobe "hot  
fixes" this profile, when used as softproof, but this is just hidding  
the profile error, which is something that lcms does not.

You can also try the icc profile inspector available in the ICC site  
(www.color.org) If you take a look on the rel.col table (B2A1), the  
output curves seems a little bit off when compared with the perceptual  
table (B2A0) which is correct.

> 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?

I would try to either to found another profile that represenst the  
standard, or to build one by using argyll and the measurement set  
available on ICC site. See below:

http://www.argyllcms.com
http://www.npes.org/Portals/0/standards/docs/CGATS21-2-CRPC1.txt


Regards
Marti Maria

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

[Boudewijn R. <bo...@va...>]

Would it be technically possible to create another icc profile that does some pre- or post-correction to work around this profile's bugs? It seems it's pretty widely used and recommended, for some weird reason.

On zaterdag 7 december 2019 21:49:10 CET Mar...@li... wrote:
> 
> Quoting 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...).
> 
> In the thread you mention, there are other people that found the  
> profile to be buggy in photoshop. So, I have further investigated this  
> profile, and found the source of problems on the B2A1 table, that is,  
> the relative colorimetric proofing direction. It is broken. It seems  
> to me that it is implementing some sort of absolute colorimetric,  
> which would be emulating the paper white. Some products of Adobe "hot  
> fixes" this profile, when used as softproof, but this is just hidding  
> the profile error, which is something that lcms does not.
> 
> You can also try the icc profile inspector available in the ICC site  
> (www.color.org) If you take a look on the rel.col table (B2A1), the  
> output curves seems a little bit off when compared with the perceptual  
> table (B2A0) which is correct.
> 
> > 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?
> 
> I would try to either to found another profile that represenst the  
> standard, or to build one by using argyll and the measurement set  
> available on ICC site. See below:
> 
> http://www.argyllcms.com
> http://www.npes.org/Portals/0/standards/docs/CGATS21-2-CRPC1.txt
> 
> 
> Regards
> Marti Maria
> 
> 
> 
> _______________________________________________
> Lcms-user mailing list
> Lcm...@li...
> https://lists.sourceforge.net/lists/listinfo/lcms-user
> 


-- 
https://www.valdyas.org | https://www.krita.org