[Digikam-users] Why does adding a keyword make the file size smaller?

[Arnd Baecker]

On Sat, 5 Jan 2008, Thomas Lunde wrote:

> Gilles -
>
> I just wanted to follow up with you about why adding a keyword to a
> file made the file size smaller.  It seems that digikam must be
> deleting some information when it does this and that worries me.

Fair enough ;-)

> If you haven't had time to look at this, I understand.

You might try to investigate yourself a bit:
E.g. you could try to compare the meta-data information
before and after using exiv2 and/or exiftool.
Maybe one can extract the mere image and check if this
stays unchanged (it should!).
You could also try to manually simulate what digikam
does by adding the corresponding field using exiv2.
As digikam uses exiv2 in the end to read/write metadata,
it might be possible to track it down in this direction.

Best, Arnd


> Thanks for any help you can provide
> Thomas
>
>
> On Dec 16, 2007 1:36 PM, Gilles Caulier <caulier.gilles at gmail.com> wrote:
> > Thomas,
> >
> > Can you send me the touched and untouched images in private to test here ?
> >
> > Gilles Caulier
> >
> >  2007/12/16, Thomas Lunde <tlunde at gmail.com>:
> > >
> > >
> > >
> > > Hello -
> > >
> > > Is it expected that adding a keyword should make the image's file size
> > > smaller?  Digikam seems to have done so here.
> > >
> > > Does anyone know what (metadata?) would have been deleted from the
> > > original file as this tag was added?
> > >
> > > I was surprised at this, so I tried it again and got the same result.
> > > bottles-unchanged.jpg is a JPG image from a Panasonic DMC-FX12 digital
> > > camera.  Other than having its filename changed, no modifications have
> > > been done to it.  I copied the file off of the camera by inserting the
> > > card into the SD card reader in my laptop and using a file manager to
> > > copy it to my hard drive.
> > >
> > > bottles.jpg is a copy of this image which was made available to
> > > digikam.  The only thing that I (intentionally) did was to add a tag
> > > called "bottles" after having turned on the option (Settings ->
> > > Configure digikam -> Metadata -> IPTC Actions -> X save image tags as
> > > "Keywords" tag) to sync the tags back to the file.
> > >
> > > Use of strings shows that bottles.jpg has the tag and
> > > bottles-untouched.jpg does not.  See also:
> > >
> > > tlunde at noir:~/Desktop$ ls -asl bottles*
> > > 2188 -rwx------ 1 tlunde tlunde 2236340 2007-12-15 16:03 bottles.jpg
> > > 2200 -rwx------ 1 tlunde tlunde 2247707 2007-12-15 16:03
> > bottles-untouched.jpg
> > > tlunde at noir:~/Desktop$
> > > [Ignore the timestamps; these have been moved back and forth to
> > > another file system via scp so the original timestamps are
> > > unavailable.]
> > >
> > >
> > > tlunde at noir:~/Desktop$ grep bottle bottles*
> > > Binary file bottles.jpg matches
> > > tlunde at noir:~/Desktop$
> > >
> > >
> > > tlunde at noir:~$ dpkg -l |grep kam
> > > ii  digikam                                    2:0.9.2-2ubuntu2
> > >              digital photo management application for KDE
> > > ii  digikam-doc                                0.9.2~beta2-1ubuntu1
> > >              handbook for digikam and showfoto in several languages
> > > tlunde at noir:~$
> > >
> > > If there are packages of 0.9.3 for ubuntu gusty, I'll be happy to try
> > > those and see if the result is the same.
> > >
> > > Thanks for any guidance.
> > > Thomas
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