(Pipeline, Hawaii, 2015).
In this article I will talk about Lightroom Previews and their effects on freeing disk space, restoring missing files and enhancing performance. This might seem an obscure and esoteric topic but there are items in here of interest to everyone using Lightroom, even including people on old and slow PCs. We will discuss:
- What are previews?
- Saving disk space by trimming your Lightroom catalogue
- Missing and excluded images
- Regenerating missing images
- Speeding processing with smart previews
- Optimising performance in Lightroom and Photoshop
What are Previews?
Lightroom creates a variety of previews to speed up display and processing of images.
Standard previews are by default the number of pixels your screen is wide so you can quickly see an image filling up the screen. This only applies to the Library module (except briefly in the Develop Module while the RAW file renders).
1:1 previews allow you to zoom in to 1:1 in images displayed in the Library Module (i.e. not in Develop).
There are also smart previews but we will discuss them separately later.
You can see the settings defined for your previews in the Edit/Catalog Settings/File Handling dialogue.
- Standard previews default to your monitor resolution.
- The setting “Preview Quality: High” relates to thumbnails.
- You can set to discard your 1:1 previews after a day, a week, a month or never.
You can define previews when you import files, by specifying a value for “Build Previews” under File Handling in the top right corner of the Import dialogue.
Alternatively, you can select files in Lightroom and use the command Library/Previews/Build Standard Previews or Library/Previews/Build 1:1 Previews.
If you don’t have a problem with disk space you might as well retain 1:1 previews indefinitely and create them while importing files. This slows down import but makes Lightroom run faster. If you don’t define 1:1 previews, Lightroom will create them on the fly with a significant impact on performance in the Library module.
Saving disk space by trimming your Lightroom Catalogue
One of the ways you can improve the performance of Lightroom is to use an SSD as the hard disk for your catalogue. Since the storage capacity may be small, the size of your Lightroom Catalogue may become a problem. For example, when I put my catalogue on my new 500GB hard drive (an M.2 SSD), I found I was left with less than 10% free space, too little for reliable performance. So I had to find a way to reduce it.
There are four elements associated with the catalogue
- The Catalogue itself. Mine was 3.6GB. I have seen people advocate clearing Develop versions in Lightroom but that seems to me a waste of time. You lose functionality and only save a couple of gigabytes, which does not solve the problem.
- Catalogue backups. I had 22.7GB here and you can save some space by deleting old backups but this wasn’t enough to solve this problem.
- The Cache. Many versions ago, Lightroom benefited from a huge cache but this is no longer required. The default is 1GB and you can have more than that but 10GB will be plenty for most people. Stored cache files may build up to a few GB and you can clear them with Edit/ Preferences/ File Handling/ [Purge Cache].
- The Previews. This is where all the files were, 391.3GB in my case. Reducing this is not as easy as one might think.
Catalogue backups offer some scope for space saving by changing the drive where you store the backups. You can’t set this from inside Lightroom but you can change it in the dialogue that appears when Lightroom is about to make a backup. It also makes sense from a security point of view to have the backups on a separate drive to the catalogue.
Previews is where all the action is though for saving space. We saw above that you can discard 1:1 previews after a day, a week, a month or never. I had mine set to Never but you’re supposed to be able to remove them with the command Library/Previews/Discard 1:1 Previews. I decided to remove all 1:1 previews for images rated at less than 3 stars (85% of my images) but it only reduced the stored previews by 0.4%. I then read on an Adobe performance guide that this only works where the standard preview size (2560px in my case) is less than half the resolution of images from your camera (4193px for the Nikon D3s). So I reduced the standard preview size to a low number, reopened Lightroom and tried again. That was better but not much. I only reduced the stored previews by 5%.
So that left only one option – to delete the Previews file and start again. In other words, I deleted the folder Lightroom Catalog Previews.lrdata under the folder for the Lightroom catalogue.
Whoompa! Previews to zero! Lightroom still works!
So what do I need previews for again?
- Standard previews let you quickly see the image full screen in the Library module.
- 1:1 previews let you zoom into 100% in the Library module, for example to compare the sharpness of one image against another to determine what to delete or what to retain. This doesn’t apply to viewing images in the Develop module or zooming in one-to-one because there you are accessing the actual RAW file.
My next step was to create new 1:1 previews using the Lightroom command Library/Previews/Build 1:1 Previews (see previous image). I decided to create them for all my images with 3 stars or more, plus current working folders. That took a long time. More than a day and a half for 23,000 images. After that I had a previews folder 141.4GB in size, 64% smaller than it was. That solved my disk space problem. Lightroom also seemed to create standard previews for all images automatically, which I wasn’t expecting.
Missing and excluded images
On the left-hand side on the library module, right click on a folder and select “Synchronise folder…” .
The Synchronise Folder dialogue appears. It may show you have photos in that directory that have not been imported into Lightroom, or photos in the catalogue that are missing on your hard drive.
If [Import New Photos] shows images in that folder that are not in Lightroom, you can click [Synchronize] to import them and see what they are. After the import, you can select them all under “Previous Import” at top left of the Library Module and then click on their folder (left pane in Lightroom) to compare the new selected images with the ones already there. They may be images you want to have in your catalogue or they may be images you meant to delete from the disk but instead just removed from Lightroom.
Missing photos may simply have been moved in Windows Explorer (so Lightroom doesn’t know where they are). If you have some, you can click [Show Missing Photos] to see what they are. You can then click on the little exclamation mark that appears at the top right corner of an image to locate them. Alternatively, the missing images may have been deleted or lost.
However, before you remove any previews, especially 1:1 previews, you should check that you don’t really need them. As we shall soon see, you may soon be able to use the previews to recreate missing images.
Regenerating missing images
A few years ago, I had three hard drives fail within a week, two in my main data drive (a RAID array) and one in my Drobo backup (essentially another RAID array). When the smoke cleared (metaphorically), I realised I had holes in my backups. Whole directories of files now showed in my Lightroom catalogue as missing. Fortunately, I left them there and did not delete the previews. Quite recently, I realised I could regenerate those missing images which were still in my catalogue, using Jeffery Friedel’s Preview Extraction Tool. Because they were 1:1 previews I was able to recover them as full-sized jpegs, good enough to print from.
You can have to copy the regenerated images to a different location, but you can copy them all into a single folder or preserve a whole folder structure. You can also retain image metadata and Lightroom’s metadata including star ratings and colour labels.
Speeding processing with smart previews
Normal previews and 1:1 previews speed operations in the Library Module; smart previews speed processing in the Develop module. They are actually miniature RAW files and save in a folder under your catalogue taking about 2% to 5% of the space of the photos themselves. They were introduced some years ago as a means to let you keep processing while disconnected from your data when travelling. However, they are just as useful to greatly improve response time in normal editing.
First you need to generate the smart previews, which you can do on import or by the command Library/ Previews/ Build Smart Previews (see third screen shot above).
In current versions of Lightroom (from CC2015.7 and 6.7), you can select a checkbox to use smart previews instead of originals for image editing. (Edit/ Preferences/Performance).
Changes transfer instantly to the original RAW files, and stay there even if you discard the smart previews. The only limitation is for sharpening and noise reduction; custom sharpening done on a smart preview will not transfer well to the original file. However, if you zoom to 1:1, Lightroom is showing you the original file so it is safe to use smart previews with custom sharpening, as long as you do that at 1:1.
If you are using an earlier version of Lightroom, you need to trick it that your folder is offline. If you close Lightroom, rename the folder say by adding ” xxx” at the end, then reopen Lightroom, you are working with your smart previews. To transfer the changes to your RAW files, you will need to close Lightroom and rename the folder back.
You might retain smart previews indefinitely if you’re not short of disk space. Still, you only use smart previews when you’re processing in Develop module so you may not need to keep them for long. Unlike the 1:1 previews, discarding smart previews works OK.
Optimising performance in Lightroom and Photoshop
The specification of your PC is one of the main factors affecting the performance of Lightroom and Photoshop. I wrote an article about that a while ago. A new generation of chipsets and motherboards has come out but everything else should be pretty much unchanged:
Adobe also provides useful guides to optimising performance in Lightroom and Photoshop:
- To increase Lightroom performance by running it on a small fast SSD, you may need to reduce the size of your Previews file
- You may be able to recover deleted or lost images by regenerating files from the 1:1 previews
- Standard and 1:1 previews speed Library module operations; smart previews speed Develop module operations