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
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.
Created attachment 94889 [details] jpegloader.patch Patch for this problem, better quality of 4:2:2 images. Maik
Thank you for quickly addressing this. I confirm that the patch fixes the problem.
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
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