Why does adding a keyword make the file size smaller?

[Thomas Lunde-2]

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@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@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@noir:~/Desktop$ grep bottle bottles*
Binary file bottles.jpg matches
tlunde@noir:~/Desktop$


tlunde@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@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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[Gilles Caulier-4]

Thomas,

digiKam use Exiv2 library to play with metadata. Witch version you use ?

Can you send me the touched and untouched images in private to test here ?

Gilles Caulier

2007/12/16, Thomas Lunde <[hidden email]>:

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@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@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@noir:~/Desktop$ grep bottle bottles*
Binary file bottles.jpg matches
tlunde@noir:~/Desktop$


tlunde@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@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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[Thomas Lunde-2]

On Dec 16, 2007 1:36 PM, Gilles Caulier wrote:
> Thomas,
>
> digiKam use Exiv2 library to play with metadata. Witch version you use ?

I'm not 100% sure how the packaging on ubuntu is set up, but this
might tell you:
tlunde@entrepot:/var/log/mythtv$ dpkg -l |grep exiv
tlunde@entrepot:/var/log/mythtv$ dpkg -l |grep xiv
tlunde@entrepot:/var/log/mythtv$ dpkg -l |grep exif
ii  libexif12                                  0.6.16-1
               library to parse EXIF files
tlunde@entrepot:/var/log/mythtv$



> Can you send me the touched and untouched images in private to test here ?

Yes, they're headed to your private email right after this message.

Obviously, it is a bad quality shot from a photographic point of view.
 I used a "junk" image just in case I accidentally overwrote the
original while I was working with it.

Thanks for the help!
Thomas
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[Thomas Lunde-2]

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.

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

Thanks for any help you can provide
Thomas


On Dec 16, 2007 1:36 PM, Gilles Caulier <[hidden email]> wrote:

> Thomas,
>
> Can you send me the touched and untouched images in private to test here ?
>
> Gilles Caulier
>
>  2007/12/16, Thomas Lunde <[hidden email]>:
> >
> >
> >
> > 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@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@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@noir:~/Desktop$ grep bottle bottles*
> > Binary file bottles.jpg matches
> > tlunde@noir:~/Desktop$
> >
> >
> > tlunde@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@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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[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 <[hidden email]> wrote:
> > Thomas,
> >
> > Can you send me the touched and untouched images in private to test here ?
> >
> > Gilles Caulier
> >
> >  2007/12/16, Thomas Lunde <[hidden email]>:
> > >
> > >
> > >
> > > 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@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@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@noir:~/Desktop$ grep bottle bottles*
> > > Binary file bottles.jpg matches
> > > tlunde@noir:~/Desktop$
> > >
> > >
> > > tlunde@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@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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> https://mail.kde.org/mailman/listinfo/digikam-users
>
>

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[Thomas Lunde-2]

On Jan 5, 2008 9:53 AM, Arnd Baecker <[hidden email]> wrote:
> 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.



Oops.  My was meant to be personal to Gilles and not to the list as a
whole.  Sorry.

In any case, thanks for the suggestions on how to investigate this
further.  If I still can't figure it out, I'll reply back.

Thomas
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[Gilles Caulier-4]

2008/1/5, Thomas Lunde <[hidden email]>:

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.

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

Metadata are managed by Exiv2 library. Andreas Huggel is the author of this lib and the more appropriate guy to respond to this question. I recommend you to contact him. Look in www.exiv2.org

Gilles

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