Seán Duggan: Working Smart with Smart Previews in LR5, Part 2
Jul 2013 02

Part 1 of this article covered some of the ways that using Smart Previews in Lightroom 5 can help improve your workflow, particularly if you’re traveling and using a laptop. In this follow-up piece, I’ll delve a little deeper to explain just how Smart Previews affect the file size of your Lightroom catalog, as well make suggestions concerning how and when you should take advantage of them.

How Smart Previews Affect Catalog Size

The addition of Smart Previews will make the file size of your Lightroom catalog larger. Fortunately, the lossy DNG files at the heart of these previews are fairly compact and much smaller than the Raw originals. With a standard DSLR 3:2 aspect ratio, the 2540 pixels on the long side of a Smart Preview are comparable to a 4.3 megapixel file.

Using four different images from a Canon 5D Mark III as test subjects, the Smart Preview files for these photos tipped the scale at 700k, 948k, 1.3MB, and 1.9MB. Images that are more visually complex in terms of high frequency detail and color variation will yield larger Smart Preview file sizes, but on average, I found the Smart Preview DNGs to be about 1MB each. In my test catalog the presence of 1,023 Smart Previews increased the catalog file size by 1GB.

When to Use Smart Previews

Since Smart Previews do increase the size of the catalog, it makes sense to develop a plan for how to use them. Although needs may vary depending on the situation, it’s unlikely that you’ll need them for every photo in your catalog. If a little over 1,000 Smart Previews lead to a 1GB increase in catalog size, you can imagine how much the catalog file size would expand if they were generated for every file in a large catalog of images! Of course, if hard drive space is not an issue then feel free to indulge, but that is typically not the case for most people traveling with a laptop.

Since laptop hard drive space is always at a premium on my smaller 256GB SSD drive, I tend to generate Smart Previews only for the images that I know I will be working on while I’m traveling. Typically this is project-specific work I may take with me on the trip and I can easily create the Smart Previews for a group of images before I leave using the menu command found in Library > Previews > Build Smart Previews.

For new photos I create on the trip, I generally create a trip-specific catalog with the images stored on an external hard and backed up to another external drive (this travel catalog is merged with my main catalog once I get back home). Since this catalog only contains images from the current trip and is smaller than the primary catalog that contains most of my images, I typically will create Smart Previews for those current trip images so I can work on them when using the external drive is not possible, such as being in the middle seat on a long flight.

Although there is the option to build Smart Previews when I import images, I usually do not generate them at that point. This is because I know that if I am being a good editor of my own photos, I will be flagging a lot of those images for deletion. Once I’ve made an initial culling pass through the day’s images and deleted the obvious rejects, then I will build Smart Previews for the shots that survived that first pass. Of course, if you’ll be on a flight right after photographing a big event such as a wedding, and you want as much flexibility as possible to edit on the go, then creating Smart Previews during the import process may make sense for you.

Discarding Smart Previews

Once you arrive back home and are able to connect to your external hard drives, it may make sense to discard the Smart Previews, thereby reducing the overall file size of the Lightroom catalog. To do this, select the images that no longer require Smart Previews and choose Library > Previews > Discard Smart Previews. A dialog will appear asking you to confirm this choice. You can also discard Smart Previews on a per image basis by selecting a file and clicking on the image status line just under the Histogram in the Library and Develop Modules.

If you have multiple files selected, the image status is displayed in four sections. The first is the number of originals without Smart Previews. The second number represents originals with Smart Previews. The third is the number of images where the original is offline or missing, but where a Smart Preview is being used. The fourth indicator is the number of files that are missing where there is no Smart Preview present.

With multiple files selected, you can click the second number for Originals + Smart Previews and a dialog will appear where you can discard the Smart Previews for the selected images.

Seán Duggan is a fine art photographer and the co-author of Photoshop Masking & Compositing, Real World Digital Photography, and The Creative Digital Darkroom. He leads workshops on digital photography, Photoshop and Lightroom.

  • Greg Gomez

    Hi Sean. Thanks for writing the article and explaining a great feature of LR5. When I import files, I typically create a Smart Preview along with the import. Eventually, I reject and delete many photos. When I remove the photos, do the smart previews go along with the originals to the trash bin? Also, I work on a laptop and need to conserve HDD space. Would you say that the only way to preserve my HDD space using smart preview is to be selective as to which images I create a smart preview for? Thanks, Greg