https://bugs.kde.org/show_bug.cgi?id=3D386396

            Bug ID: 386396
           Summary: Eliminate useless and misleading libpng terminal
                    message
           Product: digikam
           Version: 5.7.0
          Platform: Other
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: FilesIO-PNG
          Assignee: digikam-bugs-null@kde.org
          Reporter: elle@ninedegreesbelow.com
  Target Milestone: ---

Upon creating a new database, and probably every time digikam is run, the
following lines are printed to the terminal:

digikam.dimg: "/usr/share/digikam/data/sample-aix.png"  : PNG file identifi=
ed
digikam.metaengine: Loading image history  ""
digikam.metaengine: DateTime =3D> Exif.Photo.DateTimeOriginal =3D>=20
QDateTime(2010-07-27 06:40:05.000 EDT Qt::TimeSpec(LocalTime))
libpng warning: iCCP: known incorrect sRGB profile

For unfathomable reasons, libpng searches for and flags certain sRGB profil=
es
as problematic. Once such profile is an sRGB profile that is commonly found=
 on
Windows computers and consequently also in images downloaded from the inter=
net.
There is absolutely nothing wrong with this profile and probably nothing wi=
th
other profiles that libpng flags. But the error messages cause consternation
for users.

This GIMP bug report has a patch that shows how to eliminate this misleading
libpng "known incorrect sRGB profile" terminal message: Deal with libpng er=
ror
gracefully when exporting an image with the color profile "sRGB IEC61966-2.=
1":
https://bugzilla.gnome.org/show_bug.cgi?id=3D765850#c3

The GIMP bug report references an imagemagick forum discussion on the topic.
Quoting from the GIMP bug report:

#Begin quote:=20
The attached patch suppresses these libpng terminal warnings. It just adds =
this
option: png_set_option(pp, PNG_SKIP_sRGB_CHECK_PROFILE, PNG_OPTION_ON);

But maybe I should have added all of this as per the third-from-last post
    #if defined(PNG_SKIP_sRGB_CHECK_PROFILE) && \
        defined(PNG_SET_OPTION_SUPPORTED)
       png_set_option(png, PNG_SKIP_sRGB_CHECK_PROFILE,
           PNG_OPTION_ON);
    #endif
This option to suppress the libpng known incorrect sRGB profile warning is
available starting with libpng 1.6.11, which was released back in 2014.

#End quote.

Of course the patch attached to the GIMP bug report
(https://bug765850.bugzilla-attachments.gnome.org/attachment.cgi?id=3D33424=
1)
won't work with digiKam. But the relevant code changes to disable the png
warnings are hopefully easy to port over to digiKam.

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