Preview files have multiplied

[bob frost]

Why are there now hundreds of thousands more files in my preview folder? Some (but not all?) preview files (.lrprev) have associated files that seem to be different sizes of previews. They haven't been there in the past. What has changed?

Bob Frost

[dj_paige]

Assuming you are discussing Lightroom Classic (which you didn't really say):

You may have changed an option at Import that increases the number and size of previews. For example, at Import you had selected "Minimal Previews" and then later you selected "1:1 Previews".

But LrC uses these preveiws to speed up your workflow. If you get rid of some (or all) of them, things slow down in the Library Module whenever LrC has to generate a preview. It's a tradeoff ... more disk space for faster workflow; or less disk space and slower workflow.

[JohanElzenga]

Lightroom Classic 13.5 changed how previews are stored. In the past, a preview file contained a number of different size previews in one single file. Maybe these are now saved separately. Anyway, do not bother about it. This is not something the user needs to be concerned about.

[Ian Lyons]

> Maybe these are now saved separately.

Yes, they're now saved as separate files. The file format is JPEG, albeit with no extension.

[bob frost]

Thanks for the reply Ian, but why have some .lrprev files got associated separate size files, some separate size files don't seem to have any .lprev file with them, and some .lrprev files don't have any associated size files. Are .lrprev files redundant, and are being replaced by the separate size files. If so, my LR is presumably part way through replacing the .lrprev files. What triggers their replacement? And what about .lrfprev files? Are they being replaced?

Johan said I don't need to bother about all this, but I like to know what my program is doing when it suddenly increases my preview folder by 400,000 files! It takes longer to backup. And please don't tell me I don't need to back them up. I do, because if something happened and I lost all my previews, it takes an awful long time to regenerate them - I've done it in the distant past when LR was rather flaky at times.

Bob Frost

[Conrad_C]

Lightroom Classic is like many other database-oriented photo editors, where previews are managed as a “pyramid” of sizes. Some may be 1:1, some may be Standard pixel dimensions, a lot of them are grid thumbnail sizes, and maybe some are the size of the Navigator panel.

It’s possible that the reason you only see some sizes because not all sizes in the pyramid have been triggered yet. For example, if an image was viewed in Develop but not Loupe, then maybe there is not yet a Standard or 1:1 preview of it. Or if a folder had Standard previews generated for it on import but hasn’t yet been viewed 1:1 in Loupe, maybe it doesn’t have 1:1 previews yet. Or if a folder was imported with Embedded and Sidecar previews and has only been viewed in Grid, then it might only have grid thumbnail previews generated and no other size.

These have always existed, but since Adobe did a rewrite on the Previews code now they exist as separate files. But because they’ve always been there, what you are backing up probably hasn’t changed, only its form. However, the change may have a negative impact on backups, because it is true that due to file system overhead, transferring or backing up a given amount of data (such as 10GB) does take a lot longer as thousands of small files compared to one big file.

(The only reason that doesn’t bother me is that I’m in the group that excludes the massive previews file from backups. I understand why you back up previews, though)

[bob frost]

Hi Ian, I think I have answered one or two of my questions! I used 'Build standard previews' on 'All photographs' and that has deleted most .lrprev files and replaced them with the new separate-size files. I have now got nearly 1 million separate-size files instead of 150,000 lprev files. Strange though that there are still 1348 lrprev files left! I wonder why. The .lrfprev files are still there untouched (I think). I suppose the reason for this change is that it is faster to access one of these new files than to unpack the lrprev file to get the correct size preview.

Bob Frost

[bob frost]

To finish this saga, I deleted all the 1348 leftover .lrprev files on the assumption that they were simply orphaned previews (they all had the same create date of a couple of years ago). I then opened LRC and left it for a couple of hours to update its preview.db file, and then ran 'Build Standard Previews', which said there were none to build. So I was probably right in my assumption, and LRC runs fine. I can't detect any difference in performance with the new preview files, but maybe a hundredth or thousandth of a second is important to programmers!

Bob frost