[Bug 220312] New: Color management for CMYK images missing

[Marcel Wiesweg]

https://bugs.kde.org/show_bug.cgi?id=220312

           Summary: Color management for CMYK images missing
           Product: digikam
           Version: 1.1.0
          Platform: Compiled Sources
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: NOR
         Component: Color Management
        AssignedTo: [hidden email]
        ReportedBy: [hidden email]
                CC: [hidden email]
        Depends on: 172196


+++ This bug was initially created as a clone of Bug #172196 +++

Color management is missing when loading CMYK images.
Discussion at the bottom of bug #172196.

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[Marcel Wiesweg]

https://bugs.kde.org/show_bug.cgi?id=220312





--- Comment #1 from Marcel Wiesweg <marcel wiesweg gmx de>  2009-12-27 21:06:35 ---
Suggestions from Milan Knizek:
For digiKam, I would propose similar behaviour like in GIMP:

If the CMYK image has an embedded profile, it should be used (for thumbnail,
preview and editor).

If the CMYK image does not have embedded profile, digiKam should use the
default one from Settings (does not exist yet...).

Further, in case digiKam editor being set to ask when there is a mismatch
between the embedded and working profiles, the user should have a chance to
select CMYK profiles from drop-down list. (Now CMYK profiles are not listed.)

If the user does not set a default CMYK profile or does not use colour
management, then the current method of simple CMY -> (s)RGB conversion could be
used.

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[Marcel Wiesweg]

https://bugs.kde.org/show_bug.cgi?id=220312





--- Comment #2 from Marcel Wiesweg <marcel wiesweg gmx de>  2009-12-27 21:15:27 ---
My remarks on this:
To apply color management according to user settings, we must preserve the
original CMYK data in the image loaders (JPEG, TIFF). DImg is always expected
to contain RGB data, but when explicitly switched on before loading, and with
guaranteed conversion afterwards, we can probably do that. If it proves not to
be possible, we need to keep the data in an extra place inside the DImg
container. If we want full support, the settings and the color management
dialog need to support this as well.

Milan, any suggestion for a default CMYK profile that we can ship?

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[Milan Knizek]

https://bugs.kde.org/show_bug.cgi?id=220312


Milan Knizek <[hidden email]> changed:

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--- Comment #3 from Milan Knizek <knizek volny cz>  2009-12-28 08:29:37 ---
I will try to do some research on the issue of default cmyk profile.

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[Milan Knizek]

https://bugs.kde.org/show_bug.cgi?id=220312





--- Comment #4 from Milan Knizek <knizek volny cz>  2009-12-29 22:43:39 ---
There appears to be a standardisation effort in the industry to introduce
recommended ICC profiles for a few selected printing conditions. The printing
houses are then promoted to calibrate their printers to match the profiles.

In Europe, there is an initiative called ECI, which offers a set of ICC
profiles for download for free. Their profiles are based on freely available
specifications made by FOGRA.

Similar efforts probably exists for other parts of the world (US, Japan, etc.).

For the situations, when the printer is unknown, ECI recommends [1] to use ISO
Coated v2 300% ICC profile for CMYK images. The profile is made by ECI
according to specifications of FOGRA39L [2].

At the moment, it is unclear under which license the ECI ICC profiles are
available - I have sent them an email to confirm if free distribution with
GPL'ed software is possible.

However, since the FOGRA specifications are free, everyone can prepare the ICC
profiles on his/her own. Kai-Uwe Behrmann did so (using Argyllcms) and the
profiles are available in his project Oyranos [3].

Kai-Uwe confirmed to me:
"The Cmyk profiles in Oyranos are licensed like libpng and thus are
liberal to use and redistribute.
I wish to see the profiles distributed with Oyranos. So I would be glad
when digikam avoids placing them directly into /usr/share/color/icc .
Digikam might choose a subdirectory or a application specific path.
Otherwise I am fine."

Unless anyone else has another opinion, I would propose to use
coated_FOGRA39L_argl.icc as the standard CMYK profile for digiKam.

[1] http://www.eci.org/doku.php?id=en:colorstandards:offset "Which profile
should I use?"

[2] http://www.fogra.org/products-en/icc1.html

[3] http://www.oyranos.org/#about

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[Milan Knizek]

https://bugs.kde.org/show_bug.cgi?id=220312





--- Comment #5 from Milan Knizek <knizek volny cz>  2009-12-29 22:51:19 ---
Created an attachment (id=39440)
 --> (http://bugs.kde.org/attachment.cgi?id=39440)
CMYK ICC profile made by Kai-Uwe Behrmann with Argyllcms according to FOGRA39L
spec.

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[Marcel Wiesweg]

https://bugs.kde.org/show_bug.cgi?id=220312

Marcel Wiesweg <[hidden email]> changed:

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--- Comment #6 from Marcel Wiesweg <[hidden email]> ---
*** Bug 291356 has been marked as a duplicate of this bug. ***

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--- Comment #7 from [hidden email] ---
This problem still reproducible with digiKam 5.0.0 ?

Gilles Caulier

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           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Color management for CMYK   |Add CMYK support in Color
                   |images missing              |management
           Severity|normal                      |wishlist

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