The Lightroom catalog
If the very idea of manually applying keywords is making you dread going through an image library consisting of hundreds or thousands of images, don't worry. Lightroom gives you the ability to save commonly used keywords as one-click templates that can be batch-applied to as many images simultaneously as you desire. But it gets even better. Every digital camera file comes with some metadata tags of their own that have been embedded by the camera that created it. Called EXIF data, this includes descriptions such as exposure settings, camera name, capture date/time, lens and focal length, image dimensions, even GPS coordinates if your camera records it.
Image file vs. Catalog file
By default, Lightroom stores its metadata, including any adjustment edits you make, not inside the image files themselves, but in an actual catalog file residing on your hard drive. This is a database file that summarizes everything referenced in the catalog and is continually updated as you edit those images. This database file is designed to provide fast access when carrying out a metadata search. You can choose to manually select a file or group of files in Lightroom and save this metadata to the XMP header space of a JPEG/TIFF/PSD file or a .xmp sidecar file for proprietary raw file formats (Command/Control+S is the shortcut). You can even configure the Lightroom preferences so that the files are updated automatically in the background.
The main thing to appreciate about the catalog file is that it is a single, compact document which summarizes everything Lightroom needs to know about the its library contents. How is this centralized approach helpful? With an image browser such as Adobe Bridge, any metadata change you make, even something as simple as adding a single keyword, updates your entire image file. That means that when you do your (hopefully daily) backups, you must backup every single image file you've modified with a metadata change.
Performing the exact same modification in Lightroom, however, all you need to do is copy a single catalog file to keep your backup up-to-date. With just one relatively small document to worry about, it is even feasible to keep a backup copy of the catalog file in cloud storage, such as is included with an Adobe Creative Cloud subscription.
|Lightroom's data files are stored by default in the Pictures folder (Mac) or My Pictures folder (Windows). The most important document is the .lrcat catalog file (on the left). This file contains all the essential catalog information and needs to be carefully safeguarded. Without it, the only metadata information you will be able to access will be that stored in the files themselves.
The previews.lrdata file is also important as this will contain an archive of rendered previews for the catalog files. Lightroom uses this so it doesn't have to rebuild previously rendered image previews every time you launch the app. So you don't want to lose this either, as it can take a long while to regenerate a large one from scratch, but it can be done, as long as the catalog file is salvaged.
The Backups folder is where Lightroom-generated auto catalog backups (named by date) are stored.
So even though Lightroom gives you the option of automatically writing metadata changes into XMP (see the screenshot below), I believe it is best to keep this data stored centrally in one place: the catalog file. No matter how rigorous you are about saving the metadata, the catalog file will always contain the most up-to-date information about the metadata in all the catalog files. One exception I'd make would be if you need to maintain compatibility between Lightroom and Bridge. In such case, it is essential you have Lightroom write the changes into XMP in order for Bridge to be able to read the Lightroom edits.
|If you open the Catalog Settings (Lightroom > Catalog Settings…) this opens the dialog shown here where there is the option to enable 'Automatically write changes into XMP'.|
If you've read this far, it should be obvious that maintaining regular, current backups of the Lightroom catalog file is absolutely essential. In the event that your Lightroom library stops working properly the catalog file is always the first thing you’ll want to salvage. This can be done by either running a repair on the current catalog or reverting to the most recent backup version. This can be a backup catalog you created manually when prompted to do so by Lightroom, or it might be one that was saved during a regular, scheduled system backup. Keep in mid that even if you've been automatically saving metadata changes into the XMP of individual images, certain catalog information such as collections and virtual copies are stored exclusively in the catalog file.
In summary, the Lightroom catalog approach is more economical compared to browser viewing and offers a more robust approach to the management of image data. While it is possible to do most of what can be done in Lightroom using an image browser like Adobe Bridge, hopefully the insights I have provided here show why the catalog approach is more versatile and can ultimately offer you greater potential security. Whether you're a longtime photographer or just starting out, we can all expect our photo libraries to mushroom in size in the coming years. Therefore, now is a good time to be thinking about the most suitable strategy for managing your photos – not just for today, but long into the future.
Martin Evening is an award winning advertising and fashion photographer based in London, England. He is also a best-selling author of instructional titles such as The Adobe Photoshop Lightroom 4 Book and Adobe Photoshop CS6 for Photographers.