Lightroom process all kind of raw files. You have the choice of converting to or using JPEGs, Native RAW or DNG RAW.

The standard way of storing all the extra information such as IPTC, keywords… is to save them in an extra file with the same name as your photo but with an extension of XMP. So you end-up with 2 files: Test-20090130-0003.cr2 and Test-20090130-0003.xmp. That second file is called the sidecar, because it’s supposed to come along with the main file, the photo.

  1. I convert all of my photos, during the Lightroom import, to DNG. Why? No, it’s not because it’s supposed to be universal or an open source format. Some time ago, not too long ago, I really did screw-up some wildcard expansions in a script, and lost all the XMP files. Even with the backups and restores, it took days to recover most of it.
  2. I convert all of my photos, during the Lightroom import, to DNG because all the extra information, such as the IPTC, the keywords… are stored in the DNG file. There is no need to look after the XMP files.
  3. When Lightroom makes a change to the IPTC data, it stores it in its database. You just need to make sure to: Ctrl-S to save the change to the physical file.
  4. In the catalog settings: Edit > Metadata tab > Checkmark: "Automatically write changes to XMP" if you will NOT be using the DNG format.
  1. All RAW formats, which I know off, are TIFFs with a JPEG preview in front and some proprietary fields for their own extra info.
  2. DNG files processed by Adobe are usually smaller than the RAW files.
  3. DCRAW from David Coffin runs on “every platform”, including OSx, Windows, Linux, Amiga… and is free!
  4. DCRAW always has the latest in file format, often before the camera manufacturer releases their latest camera.