My Experience with Lightroom Smart Previews

When I tested my Z50 with bird photography I generated a lot of images. In one day I took over 1400 images, which, as it turns out, nearly filled the free space on my MacBook Air. Up until recently I’ve kept two Lightroom libraries – a full library on my external RAID drive with 40,000 – 50,000 images in it, and a smaller library on my MacBook with about 8,000 images in it. The MacBook library is my working library and takes up about 200 GB but tends to grow and shrink as I add and remove photos. When I go out on an excursion I load in many photos and have to start cleaning other stuff off of my 500 GB SSD to make room. It’s a system that works, but it’s annoying.

Adobe has had this concept of Smart Previews since 2013, but I didn’t try them until recently. Smart Previews are scaled down versions of RAW files (about 5 mp) that sacrifice resolution and some detail to take significantly less space while still allowing RAW editing. The Smart Previews can stay on my MacBook and the full-size RAW files stay on an external drive. I can edit on the go and plug in my external drive if I want to see extra detail or export large images. This has been a huge help to my space issue, bringing my 200 GB photo library down to 8 GB. Now I can keep a download or two on my Mac without constantly deleting things.

Smart Previews can (and maybe should) exist with regular previews

I generate standard previews when I import photos so I still had them around when I converted my library to Smart Previews. After generating Smart Previews I figured I could delete the standard previews, so I renamed preview file as a test. As soon as I did, I lost all of the previews in Library view. All of my library thumbnails were blank, but regenerated as I scrolled through. Sure enough there was a new previews file starting to fill up alongside the Smart Previews file. After scrolling through all 8,000 photos by hand (I couldn’t find a way to do it for the entire library), I ended up with a multi-gigabyte preview file, but it was significantly smaller than my old file.

The problem with this new preview file is that it was built from low-resolution Smart Previews. Smart Previews are not designed to view 100% resolution, which is something I need when checking to see if bird eyes are acceptably sharp. I could plug in my external drive to get full resolution zoom, but that defeats some of the purpose of Smart Previews. The solution: generate standard previews at 100% resolution. I ended up with a preview file that is 4x larger than the Smart Previews file, but it’s still smaller than what I had before and I can zoom into the detail I need.

Two kinds of previews make things awkward

While standard previews allow me to zoom in 100% to check critical focus when viewing my photos, Smart Previews don’t allow me to do that when editing. If I zoom into an image to check focus and then decide to edit it, Lightroom abruptly resets the view and can’t zoom in as far as before. I get this because the Smart Preview is lower resolution than the standard preview used for viewing.

100% zoom on a full-resolution standard preview (left) vs 100% zoom on a Smart Preview (right)

Editing images causes syncing issues with standard previews. Once edited, sometimes the preview doesn’t update and no longer matches the edited image. Other times it does update, but can no longer be zoomed at full resolution. That makes sense since Lightroom has to generate a new preview from the lower-resolution Smart Preview, unless the drive with the full RAW files is present, of course. As far as I’ve seen Lightroom won’t update the standard previews to match full-resolution edits automatically once the drive with RAW files is connected; it has to be done manually.

Exports need to be considered carefully

Smart Previews are 2,550 pixels on their longest side and can be exported as JPEGs within those dimensions. I gave this a try and realized that I had to be careful. First, Lightroom doesn’t prevent you from creating larger images than a Smart Preview can support. It displays a generic warning about generating exports from a Smart Preview but doesn’t tell you what you need to consider and doesn’t warn if you choose an image size larger than the Smart Preview can support. I wasn’t paying attention and exported images that were 100 or so pixels larger than a Smart Preview and received a nice batch of badly scaled up images.

After scaling down my requirements and exporting again I ran into a different problem: odd sharpening and artifacts in the sky. Take a look at these images below. They are the exact same dimensions, but one was generated from a Smart Preview (left) and one was generated from the original RAW file (right). The sky gradient is blocky and pixelated and the bird is over sharpened.

Smart Previews appear to retain the editing characteristics of the original RAW file

I pulled the exposure down a few stops on an overexposed bird photo and the Smart Preview looked great. I was impressed that it hadn’t removed any detail hidden in the highlights as far as I could tell. I’ve also bumped exposure and shadows up several stops and seen plenty of detail come out of dark areas. Gradation between similar tones, usually the sky, are not as smooth as the original RAW file, but they are enough to perform most of my editing. Sharpening, clarity, color, and masking adjustments all look good. Smart Previews deliver on their promises from an editing perspective.

Overall Smart Previews are still valuable

Despite some idiosyncrasies, Smart Previews deliver on their promise to enable editing on the go while allowing access to full RAW files when they are connected.My 8,000 photo working library takes up 48 GB on my MacBook Air for 292 GB of RAW files on an external drive. I’ve also got a copy of my entire 50,000 photo library from my external RAID drive at my fingertips, with 150 GB to spare.

I still prefer having full-sized RAW files on my Mac and will still consider 1 and 2 TB options on my next one, but for now Smart Previews allow me more flexibility than I had before.

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