[Digikam-devel] Odp: XMP metadata and GPS support

Gilles Caulier caulier.gilles at gmail.com
Wed Jun 20 09:21:09 BST 2007

2007/6/20, Andreas Huggel <ahuggel at gmx.net>:
> On Wednesday 20 June 2007 10:50, Andreas Huggel wrote:
> > Would it help in the short term if Exiv2::Image provided some kind of
> > getXmp/setXmp methods (at least for JPEGs) which would just deal with
> > std::string BLOBs containing the raw XML? This would allow to
> > read/write the data using Exiv2::Image::read/writeMetadata but
> > require some other means to parse the XML.
> FWIW, I've added Exiv2::Image::xmpPacket() which can be used to dump the
> XMP packet of JPEG images (APP1 XMP segment) and TIFF or related RAW
> images (IFD0 tag 700) as per the XMP specs. Read-only access for a
> start and no parsing of the XML yet.
>     http://dev.robotbattle.com/cmtinfo_svn.php?r=10
> Note that this is in branches/unstable only for now.


BTW, the XMP specs (p93) highlight that XMP in JPEGs suffers the same
> problem as Exif:
> "IMPORTANT: Following the normal rules for JPEG sections, the header
> plus the following data can be at most 65535 bytes long. The XMP Packet
> cannot be split across the multiple APP1 sections, so the size of the
> XMP Packet can be at most 65502 bytes."
> And that's plain (UTF8) XML code, not even compressed.

If i remember, we can use an Adobe XML packet as byte array (witch is
certainly compressed...). Right ?

Note than TIFF and PNG do not have size limitation.

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