[digikam] [Bug 353608] New: The preview is blocky, seems to use chroma subsampling

[DrSlony-4]

https://bugs.kde.org/show_bug.cgi?id=353608

            Bug ID: 353608
           Summary: The preview is blocky, seems to use chroma subsampling
           Product: digikam
           Version: 4.12.0
          Platform: Gentoo Packages
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: Preview
          Assignee: [hidden email]
          Reporter: [hidden email]

The preview is blocky in areas of highly saturated red, the effect looks like
chroma subsampling (though it might be something else entirely, since why would
it get resampled?). Image zoomed to 100%. I thought maybe LCMS was doing
something, but its the same when I turn color management off.
I was previewing this image: http://londonlight.org/i/2015-10-01_k10d_9.jpg
This screenshot shows what happens in digiKam vs Geeqie on the left.
Look closely at the circled area
http://filebin.net/ca6id4n3of/scrot_2015-10-06_163914.png
Same strange thing when I open it in the image editor.

Fine in RawTherapee, Gwenview, Geeqie and GIMP.

Reproducible: Always

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[DrSlony-4]

https://bugs.kde.org/show_bug.cgi?id=353608

DrSlony <[hidden email]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|The preview is blocky,      |The preview has blocky
                   |seems to use chroma         |artifacts reminiscent of
                   |subsampling                 |chroma subsampling

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[DrSlony-4]

https://bugs.kde.org/show_bug.cgi?id=353608

DrSlony <[hidden email]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |critical

--- Comment #1 from DrSlony <[hidden email]> ---
I just found that it's not only the preview but also the saved image which has
artifacts. This means digiKam breaks every single photo it saves!!! (though the
breakage is not easily visible unless you're working with highly saturated
colors)
imagemagick has a very useful "compare" function. I opened the image in
digiKam's editor and saved to PNG. The comparison should be identical, but
  compare 2015-10-01_k10d_9.jpg 2015-10-01_k10d_9.png c.tif
leads to
  http://i.imgur.com/RgBqnSq.png
and these differences/artifacts are very easy to see in the preview and in the
saved PNG.
Changing priority to critical as this means essentially digiKam breaks photos.

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[Maik Qualmann]

https://bugs.kde.org/show_bug.cgi?id=353608

Maik Qualmann <[hidden email]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |[hidden email]

--- Comment #2 from Maik Qualmann <[hidden email]> ---
Created attachment 94889
  --> https://bugs.kde.org/attachment.cgi?id=94889&action=edit
jpegloader.patch

Patch for this problem, better quality of 4:2:2 images.

Maik

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[Maik Qualmann]

https://bugs.kde.org/show_bug.cgi?id=353608

Maik Qualmann <[hidden email]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|The preview has blocky      |The preview has blocky
                   |artifacts reminiscent of    |artifacts reminiscent of
                   |chroma subsampling          |chroma subsampling [patch]

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[DrSlony-4]

https://bugs.kde.org/show_bug.cgi?id=353608

--- Comment #3 from DrSlony <[hidden email]> ---
Thank you for quickly addressing this. I confirm that the patch fixes the
problem.

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[Maik Qualmann]

https://bugs.kde.org/show_bug.cgi?id=353608

Maik Qualmann <[hidden email]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
   Version Fixed In|                            |4.14.0
         Resolution|---                         |FIXED
      Latest Commit|                            |http://commits.kde.org/digi
                   |                            |kam/d92ef8575e5671cc102875f
                   |                            |fc48bbb2a87bdfc9a

--- Comment #4 from Maik Qualmann <[hidden email]> ---
Git commit d92ef8575e5671cc102875ffc48bbb2a87bdfc9a by Maik Qualmann.
Committed on 08/10/2015 at 17:18.
Pushed by mqualmann into branch 'master'.

apply patch #94889 to change the JPEG decompression parameter for a better
quality
FIXED-IN: 4.14.0

M  +2    -1    NEWS
M  +1    -1    libs/dimg/loaders/jpegloader.cpp

http://commits.kde.org/digikam/d92ef8575e5671cc102875ffc48bbb2a87bdfc9a

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[Gilles Caulier-4]

https://bugs.kde.org/show_bug.cgi?id=353608

--- Comment #5 from Gilles Caulier <[hidden email]> ---
Git commit 4efe671d183fd1889767c2972b3d52a80568d3af by Gilles Caulier.
Committed on 09/10/2015 at 05:30.
Pushed by cgilles into branch 'frameworks'.

backport commit #d92ef8575e5671cc102875ffc48bbb2a87bdfc9a from git/master to
frameworks branch

M  +1    -1    libs/dimg/loaders/jpegloader.cpp

http://commits.kde.org/digikam/4efe671d183fd1889767c2972b3d52a80568d3af

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