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OK, if those are regular previews, what are Smart Previews? Another good question. Smart Previews are basically a smaller version (2560 pixels on the long side) of the original that preserves many of the qualities of a raw file that make it useful for editing. This smaller version is saved as a special DNG file (I cover DNG in more depth in Chapter 7), which allows for a type of compression to make the file size in bytes smaller as well.

The original reason for the introduction of Smart Previews was to have a way to store a smaller, yet still editable, version of the original photo alongside the catalog file so that you could still perform tasks in the Develop module even if the original photo was inaccessible due to being offline. For example, I keep the majority of my photos on an external hard drive, which is not always connected. By creating Smart Previews of my photos (when needed), I can still edit them in the Develop module because Lightroom Classic is smart enough to refer to the Smart Preview when the original is not available, and then smart enough to switch back when I plug that drive back in. This has turned out to be a great compromise, because it just wouldn’t be possible to keep my external drive plugged in all the time.

The Develop module is a special case where it needs to access the original photo to be able to perform edits. If the original is offline, a Smart Preview, if created, can stand in to keep your workflow moving forward.

On a related but side note, the compact yet editable package of the Smart Preview became the key to keeping photos synced through the Adobe cloud when syncing with the new Lightroom ecosystem of apps for Mac, Windows, iOS, and Android (see Chapter 16).

Because not everyone needs Smart Previews all the time, or even at all, their creation is completely optional. You can create them from the Import process covered in Chapter 4, or afterward, in the Library module, accessed via the Library ⇒ Previews ⇒ Build Smart Previews menu. For now, you can see a running tally of how much space the cache is taking up on this tab of Catalog Settings. As with the 1:1 previews, you can manually remove them via the Library ⇒ Previews ⇒ Discard Smart Previews menu command.