Importing photographs into your catalog establishes a link between the catalog and the physical file. The photograph can exist on an internal or external drive. In previous versions of Lightroom, you could edit images that were contained on drives connected to Lightroom.
Smart Previews in Lightroom allow you to edit images that are not physically connected to your computer. Smart Preview files are a lightweight, smaller, file format, based on the lossy DNG file format.
- Smart Previews are much smaller than the original photos. You can free up disk space on devices with smaller storage capacities (for example, SSD drives) by choosing to keep original files on a high-capacity external device (for example, NAS devices or external discs). For example, 500 raw images from a high-end DSLR camera may occupy 14 GB of disk space. The Smart Preview files for the same images amounted to 400 MB of disk space.
- Continue to work with your Smart Preview files even when the device containing your original photographs is disconnected. You can perform all edits that you would perform on the original file.
- Automatically sync any edits made on Smart Preview files with your original files, as soon as the device is reconnected to your computer.
- Once created, your Smart Preview files are always up to date. When your storage device is connected, any edits you make to the original file are applied instantly to the Smart Previews as well.
When you import new images into your catalog, select Build Smart Previews (Import dialog > File Handling section). Smart Previews are created for all the images imported into the catalog.
When you export a set of photographs as a catalog, you can choose to build and include Smart Previews in the exported catalog. Click File > Export as Catalog, and then select the Build/Include Smart Previews checkbox.
On the fly
You can create Smart Preview files on demand. Select the files for which you want Smart Previews, and then click Library > Previews > Build Smart Previews.
Smart Previews are stored in the [Catalog Name] Smart Previews.lrdata file, located in the same folder as the catalog.
You can identify the Smart Preview status of a photograph based on the information displayed below the Histogram:
A. Originals without Smart Previews B. Originals with Smart Previews C. Smart Previews only (Disconnected from Original) D. Original file missing (normal preview displayed)