When using Lightroom, we have to deal with IPTC, XMP and EXIF data but what are they? Except for alphabet soup.

IPTC: International Press Telecommunications Council

It was created for the wire services in the time that news people used faxes. Remember fax machines in the 70s and the 80s? It keeps track of:

  • Caption
  • Credits
  • Copyrights
  • Bylines
  • Locations
  • ANPA, American Newspaper Publishers Association, news categories

XMP: Extensible Metadata Platform

It was created by Adobe to convert the IPTC to XML. XML = Extensible Markup Language. The XMP is a separate text file, often referred as the sidecar, because it has to ride along with the photo. If you lose or delete the XMP file, you will lose all of the extra information for managing your photos. The format is very similar to HTML. Once the IPTC information is in a XML format, it can easily be ingested and processed by databases like Oracle and Microsoft SQL Server, so it can be searched. Here’s the beginning of one of my XMP files.

<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 4.2-c020 1.124078, Tue Sep 11 2007 23:21:40 ">
 <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description rdf:about=""
    xmlns:tiff="http://ns.adobe.com/tiff/1.0/">
   <tiff:Make>Canon</tiff:Make>
   <tiff:Model>Canon EOS Tags: Lightroom</tiff:Model>
   <tiff:Orientation>1</tiff:Orientation>
   <tiff:ImageWidth>5184</tiff:ImageWidth>
   <tiff:ImageLength>3456</tiff:ImageLength>
  </rdf:Description>
...

It keeps going on for another 321 lines and that’s only for one photo. But as you can see, it’s something very simple than can be easily read. What goes into the XMP file?

  • All of the EXIF data
  • All of the IPTC information
  • Labels, ratings, comments…
  • All the steps taken by Lightroom during the edits, such as the crops…
  • Pretty much anything that you want since you can create you own tags, that’s why it’s called “extensible”

EXIF: Exchangeable Image File Format

This is information about the camera and photo taken. It’s stored inside the JPEG or the RAW photo file itself. That information is also duplicated in the XMP sidecar if you Save Metadata To File. It includes:

  • Timestamp
  • Shutter speed
  • ISO rating
  • Focal length