Storing Metadata Edits with the Photo File
Metadata edits are stored in the Lightroom catalog, but the edits also can be stored with the photo file itself. In the case of JPEG, TIFF, PSD, or DNG images, within the file’s header is a dedicated space that can be used to store the metadata. With proprietary raw files, on the other hand, this info has to be stored separately in what’s known as an XMP sidecar file.
If you choose File > Catalog Settings, you get the dialog box shown in Figure 1. The option "Automatically write changes into XMP" records metadata changes to the file as well as to the Lightroom catalog. It’s best to leave this option unchecked. With this option selected, Lightroom would update the XMP metadata continually as changes are made via the program, which would slow performance. With this option disabled, Lightroom metadata edits are stored in the internal catalog file only.
Lightroom 1.0 had the Metadata > XMP > Export Metadata to XMP menu item. This has been replaced in Lightroom 1.1 by the simpler Save Metadata to Files command with the easy-to-remember keyboard shortcut Command-S (Mac) or Ctrl-S (PC). When you’re working in the Library or Develop module, use the shortcut every time you want to export and update the metadata to a photo or a group of selected photos. In the long run, this approach will allow you to work much faster than you would with auto-update running in the background.
Figure 1 Metadata catalog settings.