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October 2004
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2004.10.03 22:45 "Re: IPTC tags", by Bob Friesenhahn
On Sun, 3 Oct 2004, Gary Lawton wrote: > > I'm trying to work out how to read and write IPTC tags into TIFF images. I've > downloaded the specification for IIMv4 from > http://www.iptc.org/download/download.php?fn=IIMV4.1.pdf and I think that's > fairly clear how an IPTC record is structured. > > But... How does this relate to the libtiff Tag Reference guide at > http://www.awaresystems.be/imaging/tiff/tifftags.html ?? Is there a private > tag description for the IPTC information or is it held inside the Photoshop > Tag (ref 34377) ? > > Am I missing something obvious? The tag for IPTC is TIFFTAG_RICHTIFFIPTC. Note that the length of this tag is the length in 32-bit words so you must multiply by four to obtain bytes. To obtain the tag: TIFFGetField(tiff,TIFFTAG_RICHTIFFIPTC,&length,&value); length *= 4; // bytes To save the tag (length in bytes): TIFFSetField(tiff,TIFFTAG_RICHTIFFIPTC,(uint32) length/4,(void *) value); There is also the issue that the content may be byte-swapped (due to being written on a different-endian CPU) so you would need to do: if (TIFFIsByteSwapped(tiff)) TIFFSwabArrayOfLong((uint32 *) value,length/4); Yes, the Photoshop profile will also contain an IPTC tag. That makes life more interesting. :-) If there is no TIFFTAG_RICHTIFFIPTC tag but there is a TIFFTAG_PHOTOSHOP then a IPTC tag can still be obtained. Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us http://www.simplesystems.org/users/bfriesen