[Digikam-users] Lossless rotation is lossy!

[Bast!]

Hmm, like I said, I checked the result of the rotation and it was indeed
lossy. Here is what I did in Gimp:

take an JPG file and duplicate it.
Open one of the images in Digikam and rotate it.
Open this image in Gimp.
drag and drop the other image into gimp, into the same project.
add it as a new layer.
rotate the layer so it fits onto the other image by
Layer/transform/Rotate 90 degrees
select the top layer and chose the mode "difference".
copy all visible (ctrl+shift+C)
paste as new layer (edit/paste as/layer)
select this layer and open the dialog Colors/levels
the value for the input levels on the right I set to 1 (from 255) and
hit ok.

If this image is totally black, and only then, the rotation was
lossless. If you see colored dots, it was lossy, since this is the
(probably not visible, but existing nonetheless) difference the rotation
introduced.

Or am I missing something?

Like I said, other means of lossless rotation tested do result in a
complete black (meaning zero difference) differencial map.

cheers
Bast!

Am 14.04.2014 16:55, schrieb Gilles Caulier:
> The JPEG transform operated from digiKam IconView is lossless. It
> use standard LibJPEG lossless code, as you can see here :
> 
> https://projects.kde.org/projects/extragear/graphics/digikam/repository/revisions/master/show/libs/jpegutils/libjpeg-80
>
>  It's the same from digiKam Import Tool.
> 
> From BQM, it's not yet...
> 
> Best
> 
> Gilles Caulier
> 
> 2014-04-13 23:56 GMT+02:00 Bast! <bast at abwesend.de>:
>> Hi Gilles
>> 
>> The current functions are NOT lossless! They have small but
>> measurable difference. In Gimp I put the original and the rotated
>> version in two layers on top of each other, chose difference as
>> layer option and adjusted the color values until i saw the
>> difference.
>> 
>> When compared to the really lossless rotation of irfanview I can
>> say that both batch rotation and the rotating buttons of Digkam do
>> in fact a _lossy_ rotation.
>> 
>> What am I doing wrong?
>> 
>> Bast!
>> 
>> Am 13.04.2014 21:13, schrieb Gilles Caulier:
>>> JpegLossLess plugin have been disabled in digiKam since a long
>>> time. A core solution is used instead and is shared with BQM. All
>>> functions previously available with JPegLossLess still here, but
>>> without to use the plugin.
>>> 
>>> Best
>>> 
>>> Gilles Caulier
>>> 
>>> 2014-04-13 17:45 GMT+02:00 Bast! <bast at abwesend.de>:
>>>> Hi
>>>> 
>>>> I cannot find the Kipi plugin JpegLossLess in Digikam and
>>>> therefore have only the lossy rotation of any kind. The
>>>> documentation refers to this plugin but I cannot find it.
>>>> 
>>>> I am running kubuntu 12.04.04 LTS, Kubuntu 13.10 and Ubuntu
>>>> 13.10 in a VM, updated the kipi plugins and digikam to 3.5.0 on
>>>> all three. Setting up kipi-plugins-common (4:3.5.0-0ubuntu10)
>>>> ... Setting up kipi-plugins (4:3.5.0-0ubuntu10) ...
>>>> 
>>>> Even the jpeglossless plugin was installed, I think: 
>>>> /usr/lib/kde4/kipiplugin_jpeglossless.so 
>>>> /usr/share/kde4/services/kipiplugin_jpeglossless.desktop 
>>>> /usr/share/locale/es/LC_MESSAGES/kipiplugin_jpeglossless.mo 
>>>> ...
>>>> 
>>>> But it is not shown in the Configuration of Digikam under
>>>> Kipi-Plugins. How do I get the lossless JPEG rotation to work
>>>> under digikam?
>>>> 
>>>> Thanks in Advance Bast! 
>>>> _______________________________________________ Digikam-users
>>>> mailing list Digikam-users at kde.org 
>>>> https://mail.kde.org/mailman/listinfo/digikam-users
>>> _______________________________________________ Digikam-users
>>> mailing list Digikam-users at kde.org 
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>>> 
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