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Without Smart Previews, you can only process photos in Lightroom Classic's Develop module if the hard drive containing your photo files is connected to your computer. If you store your photos on an external hard drive, and it isn't connected, you can't process them.
This is unlikely to be a problem if you do all your photo processing at home. But it's a disadvantage when you travel. You may prefer not to take a hard drive containing photo files with you in case it gets lost or stolen. Or you might leave external drives at home so you travel with fewer items.
In Lightroom 5 Adobe introduced a new feature called Smart Previews that solves this problem.
What is a Smart Preview?
A Smart Preview is copy of a photo file. It is a compressed, lossy DNG file that has been resized so the longest edge measures 2540 pixels. It is saved, along with all other Smart Previews belonging to the same Catalog, in an .lrdata file.
The .lrdata file type is also used to store the previews that Lightroom makes so it can display thumbnails and full-size previews of the photos displayed in the Catalog in the Library module (Minimal, Standard and 1:1 previews).
Both .lrdata files are saved in the same folder as the Catalog (which should be on your computer’s internal hard drive).
Here’s the folder showing the Catalog file and the accompanying .lrdata previews and Smart Previews files. There are three files in this folder, all relating to a Catalog containing 16 files that I exported to test Smart Previews. The .lrcat file is the Catalog itself. One .lrdata file contains previews, and the other Smart Previews.
Smart Previews are tiny. I exported the original Raw files contained this small Catalog (16 in total) and the total file size was 430Mb. The size of the Smart Previews file is only 9.1Mb. The Smart Previews file is only a little over 2% the size of the Raw files.
The compressions is very effective. When I look at a Smart Preview at 100% enlargement in Lightroom, it looks just as good to my eye as the original file. It’s just smaller, as the file has been resized to 2540 pixels along the longest edge.
When should you create Smart Previews?
If you only ever edit your photos at home, and you always have the hard drive containing your Raw files to hand, there may be no need to build Smart Previews. It takes time for Lightroom to build them, and even though they are small, they do take up hard drive space.
But if you're away from home and don’t want to take the hard drive containing the original Raw files with you, then you can build Smart Previews for the photos that you might need. Unlike 1:1 previews (which are much bigger) Lightroom doesn’t discard them unless you tell it to.
Depending on the total size of your library, you could theoretically generate Smart Previews for your entire photo collection, giving you the ability to edit any of your files in the Develop module while you are away from home. If the figures above hold true, then a library of 50,000 images can be compressed down to a 28GB .lrdata file containing Smart Previews. That’s small enough to store on most internal hard drives.
The benefits are not just for travelers. If you're a laptop user, Smart Previews make it easier to process photos in Lightroom as you don't need the hard drive containing your original photo files to be attached to your computer. You can take your laptop into another room, to the office, to a friend's house or a coffee shop and still develop photos.
What can you do with Smart Previews?
The biggest benefit of Smart Previews is that you can edit your files in the Develop module. When the hard drive containing the original files is disconnected, Lightroom uses the Smart Previews.
When you reconnect the hard drive containing the original files, Lightroom updates them automatically. This includes any changes to metadata you may have made, as well as edits made in the Develop module.
I’ve tried this out and it works very well. Lightroom accurately transfers edits made using the Spot Removal tool and Adjustment Brush as well as adjustments made using sliders in various panels. Adobe recommends that you check your editing if you have changed the Sharpening settings in the Detail panel, and I guess it is wise to do so if you have adjusted Noise Reduction as well.
This is the original Raw file viewed at 1:1 magnification in Lightroom’s Develop module. It is a 21 megapixel file measuring over 5,000 pixels along the longest edge. The red patch over the eye shows the mask created by an Adjustment Brush.
This screen shot shows the Smart Preview of the same image, again at 1:1 magnification. The only difference is that the image is smaller. The Adjustment Brush mask has also been resized so that it covers the same area as on the original Raw file.
You can also export images from Lightroom. The maximum size you can do so without upsizing is 2540 pixels along the edge, but that’s good enough for most purposes. It’s more than enough for uploading to Facebook, Flickr, 500px, Instagram or your own website (unless you need full-size photos for a specific purpose, such as photo files that may be used for creating prints or sold as stock).
If you a professional photographer with clients, it may also be large enough for you to export photo files if a client makes an unexpected request while you are away from home. This size file is large enough for many things, including magazine reproduction at most sizes.
Another use I can think of, although I haven’t tested it, is as an emergency backup. As each month goes by, you could export a Catalog containing all the Raw files from that month, plus Smart Previews, and store them offline in Dropbox, Box or a similar cloud storage service. It’s not as good as having the original Raw files, and it doesn’t take the place of a proper backup plan for your Raw files, but it may be some extra peace of mind in the event that a disaster strikes and wipes out all your original files and backups.
If you are away from home for some weeks, and have access to the internet, it may also allow you to make an emergency backup of the photos you take during that trip.
Smart Previews also allow you to work with Lightroom app for mobile, assuming that you have the app installed on a mobile device and that you are subscribed to the Creative Cloud photographers package. The app works with Smart Previews generated by Lightroom for the photo files synced with the mobile device.
Smart Previews do have a couple of limitations you should be aware of.
- If you want to export a photo to a plug-in or to Photoshop you need the original photo file. It won't work with Smart Previews.
- If you want to use the Merge to HDR or Merge to Panorama functions, then also need the original photo files. But if you have Lightroom Classic or Lightroom 6.7 or later, you can Merge photos with Smart Previews only.
Working with Smart Previews
There are several ways to generate Smart Previews.
When you import photos into Lightroom. Tick the Build Smart Previews box in the File Handling panel in the Import Window to do so.
In the Library module. Select the images for which you need Smart Previews and go to Library > Previews > Build Smart Previews. You can also choose the Discard Smart Previews option if you want to free up some hard drive space or you no longer require them.
In the Develop module. Click on the Original Photo icon in the Histogram panel to build a Smart Preview for the selected photo. However, this only lets you build previews for one photo at a time.
When exporting a Catalog. To export a set of photos as a Catalog, go to File > Export as Catalog and tick the Build / Include Smart Previews box at the bottom of the Export as Catalog window.
Note that Lightroom needs access to the original photo file to build a Smart Preview.
Smart Previews in the Library module
If an image doesn’t have a Smart Preview, and the hard drive containing the original file is disconnected, then Lightroom displays a exclamation mark icon in the Library module thumbnail to let you know that it doesn’t know where the file is. Note that this icon may also mean that the original file has been deleted or moved to another folder outside of Lightroom.
If the image has a Smart Preview, then Lightroom displays the Smart Preview icon instead, to let you know that you can process the photo in the Develop module if you need to.
Smart Previews in the Develop module
In the Develop module the Histogram panel tells you whether a Smart Preview exists.
If it says Original Photo under the histogram, you know that you are processing the original photo file, and that a Smart Preview doesn’t exist.
If it says Original + Smart Preview, then you know that you are processing the original photo file, and that a Smart Preview exists (there's an exception if you are using the latest versions of Lightroom 6 or Lightroom Classic – see below).
If it says Smart Preview, then that means a Smart Preview exists, and that you are currently processing the Smart Preview, not the original photo file.
If it says Photo is missing, that means that there’s no Smart Preview, and that the hard drive containing the original photo isn’t connected to the computer (or that the file has been moved and Lightroom doesn’t know where it is). There’s no histogram and you can’t process the image.
Smart Previews to Speed up your Lightroom Classic Workflow
There's another benefit of using Smart Previews. It turns out that Lightroom runs faster when editing Smart Previews compared to using the previews it builds for the Develop module. If you take the time to build Smart Previews for your photos, then disconnect your hard drive (it helps if your photos are stored on an external drive) you'll experience an increase in processing speed.
Latest Lightroom advances with Smart Previews
The latest versions of Lightroom 6 and Lightroom Classic have a new feature.
You can set Lightroom to automatically use Smart Previews, if they exist, in the Develop module. This even works when the hard drive containing your photo files is connected to the computer.
To enable this feature go to the Performance tab in Preferences and tick the Use Smart Previews instead of Originals for image editing box. Then restart Lightroom to make it work.
The idea is that working with Smart Previews enables you to work faster in the Develop module.
Note that if you zoom to 100% (1:1 mode) in the Develop module, then Lightroom switches to the original file even with Use Smart Previews instead of Originals for image editing enabled.
You need Lightroom Classic or Lightroom 6.7 for this to work. Check which version you have by going to Lightroom > About Adobe Photoshop Lightroom (Mac) or Edit > About Adobe Photoshop Lightroom (PC).
Lightroom Classic's Smart Previews are a very useful tool that have made Lightroom Classic easier and faster to use. As well as offering speed and convenience, they make the Lightroom mobile and Lightroom web tools for Creative Photography Plan subscribers possible.
Do you have any questions about Lightroom Smart Previews? Let me know in the comments.
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