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

[bob frost]

Not quite finished! To investigate the 1:1 previews in the new preview sytem of LRC 13.5 I created a new catalog and imported 50 nefs (about 45Mp each). LRC created new previews according to its defaults (auto - 2560 and medium quality), and looking at the new previews I have three for each image - 320, 1032, and 2064 in size.I then created 1:1 previews which added 4128 and 8256 in size. Then deleting the 1:1 previews only deleted the largest size that it had created - 8256 - and left the 4128 size that was created by the build 1:1 preview command. Interesting. No .lrprev files at all, but three .lrfprev files for the three faces in those images.

So to sum up, using 'build 1:1 previews' creates two larger sizes of the new format previews, but deleting them only deletes the largest.

Happy Lightrooming!  Bob Frost

[JohanElzenga]

"LRC created new previews according to its defaults (auto - 2560 and medium quality), and looking at the new previews I have three for each image - 320, 1032, and 2064 in size"

Are you saying that you don't have the 2560 preview? Or do you mean three extra previews?

[Ian Lyons]

When files are imported with standard-sized previews, then maximum preview size will reflect the size set in Catalog Settings. There will also be 2 or 3 other files that are ½, ¼ and 1/8 of the largest preview. However, when 1:1 previews are built the largest sized preview will either  be the cropped size or actual size with other smaller previews being ½, ¼, etc of the largest.

When the 1:1 previews are discarded, the largest preview for a cropped file will now be half of the full sized cropped files dimensions, etc.

So, from above we can see that the standard-sized preview as set in catalog setting is only applicable until 1:1 previews are built, then the cropped dimensions take over.

I've attached a screenshot that may help make above a tad clearer. The previews groups with red boundary are cropped files.

[bob frost]

Hi Ian, I've read your reply three times, but it does not tally with what LRC 13.5 has actually done in my test. To reiterate, the NEF files imported into my test catalog were fullsize from my Nikon Z8 camera so had dimensions of 8256x5504. They were not cropped either in camera or in LRC (the xmps that they had in my main catalog were left behind). On importing LRC automatically created three new preview files for each image - 2064, 1032, and 320 (according to their filenames). These seem to be correct sizes of 1/4, 1/8, and 1/32 of the actual file size (8256). Why there was no 1/16 is presumably known only by the LRC team. When the 1:1 previews were made these were 4128 and 8256, the 1/2 and fullsize previews. On deletion of 1:1s,  only the fullsize 8256 was deleted leaving the 1/2 size (4128) behind.

What seems to be misleading is the default catalog prefs entry of 'Auto (2560)'. Wondering about that for a while, I suddenly realised that it was the monitor size (Eizo CG 2730) - 2560x1440. The actual previews are not directly related to the monitor size but to the file size (8256).

I hope this clears things up?

Bob Frost

[JohanElzenga]

To me, it does not. Yes, the preview (auto) size is related to the monitor, not to the image. Change your monitor settings, and you'll see that this changes 'Auto (xxxx)' too. That makes sense, because you want to be able to see the image in loupe view on your monitor, and you want to be able to do that in full screen mode. That means you need an image that is 2560 pixels wide; the width setting of the monitor. So why Lightroom does not create that 2560 pixels preview is not clear to me. 

[bob frost]

OK, I've just done it again. Created a new catalog, imported the same 50 nefs, and lo and behold it has created 2560, 1280 and 640 previews! That is what you would expect with a 2560 monitor. But when I then created 1:1 previews, it made 8256 and 4128 previews, as expected for 8256 images(?), but altered the existing previews to 2064, 1032, and 320. The previous 2560, 1280 and 640 previews have disappeared! So in this second test, the initial creation of standard previews was in relation to the monitor size, but the second creation (using Build 1:1 previews) changed them all to be in relation to the image size(except for the 320 size).

Make of that what you will! Perhaps all this was best hidden in .lrprev files.

Bob Frost

[JohanElzenga]

Yes, this is as expected. If you create 1:1 previews and then delete them again, Lightroom Classic will not delete a preview that is close to the standard-sized preview. Instead, it will use it and delete the standard sized one.

[JohanElzenga]

To elaborate on this: If I remeber correctly, Lightroom Classic will keep a 1:1 preview if it is smaller than 2x the standard sized preview, and discard the standard-sized preview instead. That is not new, it always did that. So in your example, the 8256 preview is deleted, because it is larger than 2x 2560. The 4128 preview is not deleted, because it is smaller than 2x 2560. Instead, the 2560 is deleted. The other three previews are probably changed to 2064, 1032, and 320 because then they are again 50%, 25% and 6.25% of the new 4128 standard size preview.