[Libexif-devel] file size decreases after exif --set-value?

[Gerald O. <ge...@im...>]

Hi,

Thanks for writing libexif, gexif, exif, etc; fantastic stuff!

I am trying to use 'exif' to reset the orientation value in a jpeg
file after rotating it with jpegtran, and it seems to work well
but the file size decreases by 400 bytes during the exif step.

    $ exif --ifd=0 -tag=0x0112 --set-value=1 11-23-06.jpg 
    Wrote file '11-23-06.jpg.modified.jpeg'.

    $ ls -l 11-23-06*
    -rw-r--r--    1 gerald   1249462 Jul 10 18:27 11-23-06.jpg
    -rw-r--r--    1 gerald   1249066 Jul 10 18:28 11-23-06.jpg.modified.jpeg

This makes me a little nervous because I don't know what was lost.
It may be that libexif's canonical exif output is just a bit less
verbose than that used by Canon, but it would be nice to know I'm
not losing anything important.

I checked for a few obvious things that might have gone missing
(exif data, image thumbnail), but they're still there.

my test file came from a Canon G2:
http://impressive.net/people/gerald/2002/09/29/11-23-06.jpg

and I am using the latest released exif (0.6) and related libraries.

Does anyone know what those ~400 bytes might be?

Thanks,

-- 
Gerald Oskoboiny <ge...@im...>
http://impressive.net/people/gerald/