DNG previews corrupted in Windows Explorer views

[Sean Goodhart]

After editing some, not all, DNG files in LrC I'm finding the previews are being corrupted when the files are viewed in Windows 10 Explorer.  A screenshot of what's happening is attached.  

I've got LrC set up so that edits are being saved into the DNGs (or as side-car files for raw images I've not yet converted to DNG).

The files are not corrupted per-se, when looking using the browser in Adobe Bridge they are fine, as they are when viewed in LrC and Lr.  

Is this a Windows 10 thing?  I know I need to update my system soon...  

Is this Explorer preview failure happening for anyone else?

[dj_paige]

Corrupted previews files are caused by hardware problems. The hard disk is malfunctioning or (less likely) bad memory chips.

[Sean Goodhart]

@dj_paige these are good points to check but I don't think that's the issue.

The disk is an SSD, it's reporting zero ECC errors. That "error checking and correcting" should resolve any random bit problems anyway. As for the PCs memory, I've done a check with mdsched.exe and it reported no errors.

How would the issue I'm seeing be specifically affecting only DNG files if it were a disk or memory problem? Surely other files would also randomly suffer being corrputed.

To be clear these preview corruptions are just DNGs, so it's something software oriented in my view. It's either in the MS Windows handling of the file or the way Adobe LrC edits being written into them.  Digging a little deeper I'm noticing it's just the DNGs which were shot using my Samsung S20 Plus phone that are being impacted by this bug. Weird!

[dj_paige]

Another possibility is that you need to perform deeper diagnostics.

It is still my belief that corrupted preview files are caused by malfunctioning hardware — or as @GoldingD explains, it can be caused by syncing with the "the cloud" such as OneDrive. This is not caused by Lightroom Classic.

[GoldingD]

In your screenshot, it appears that your photos are in a folder that is being sync'd to OneDrive. Or worse yet, a drive mapping to an actual OneDrive storage.

I assume that if you were to share your Lrc system info, that the library path will also point to OneDrive (highly likely to be a sync)

LrC and OneDrive has been described in at least one LrC community discussion as "Made in Heaven" Actually many find it to be made in double Hockey Sticks. Some members find it works, that is until it does not, normally on a bad day for Internet connectivity.

I blame this on Microsoft trying to strong arm everyone into usin MS accounts instead of local accounts, and treating OneDrive for user system library file use as the best thing since sliced bread.

This might not be your problem at all, but you might consider divorcing your LrC catalog and your photo locations from OneDrive. One way is to disassociate the effected files from automatic sync to OneDrive. Another often taken, is to simply create root folders on hard drives with folder names not associated with OneDrive, and move the catalog, previews, and in your case photos. You might consider testing this out by creating a new catalog in such a folder, and importing new folders into an appropriate folder, and testing.

LrC catalogs, MUST be on a local hard drive, internal or external. They must not be on a network share, be that an actual server or a NAS (not to be confused with a DAS RAID) not the cloud. The catalog can be copy'd to the cloud, typically for a backup, and in theory via sync, but not auto sync as the OneDrive behaves. This because the OneDrive auto sync operates constantly as you edit the photos, this slows LrC down, and can lead to failures as LrC does not like competing with such a constant communication.

Photos in theory can be on the cloud, typically something like DropBox, Performance may or may not take a hit. But typically this eventually breaks, typically photos go missing in LrC probably due to a bad Internet day, and easily fixed by repointing the folder location.

[Sean Goodhart]

@GoldingD I'm one of the lucky ones who have my image files happily working in OneDrive and on NAS drives.  The OD is my "working set" (current year) folders - being actually located on the local hard drive there's no time penalty; the OD sync simply copies up the file once it is no longer open.  The NAS drives hold the files >1 year old, less likely to be being edited so I can live with the odd second of additional delay.

As you recommended my catalog does live on non-synched folders on the C: away from OD, with the monthly backups being copied to a OD folder (keeping just current and the last 3).  These are good recommendations I followed when I first got in to Lightroom (classic) about 10 years ago, has worked smoothly since the start. 

I did have a bit of a catalogue corruption last year (nothing to do with hardware issues - it was a LrC bug I found), so since then have turned on the feature to write edits immediately into the DNGs (or sidecar files) so I never lose work again.  This does cost a little in terms of time, but it's worth it for the "safety blanket".

Thanks for taking the time to write the detailed reply.  johnrellis made the suggestion which resolved my issue - it's a very interesting compatibility issue btw Windows and DNG formats, this was what was in my mind but I had no idea of the cause or fix.

[johnrellis · Accepted solution]

It could be a Windows 10 limitation. Last year LR and Camera Raw started using the latest DNG version (1.7), which uses JXL compression. It may be that Windows 10 File Explorer is tripping over that.

In LR, select a couple of DNGs that appear corrupted in File Explorer. Do the menu command Library > Convert Photo To DNG, selecting Compatibility: Camera Raw 14.0 And Later. That will convert the DNG to version 1.4, which doesn't use JXL compression.  Do those DNGs show correctly in Windows File Explorer?

[Sean Goodhart]

@johnrellis - nailed it, your suggestion is perfect.  It's a Windows issue in being able to "see" the new DNG format.

I've moved a copy of one of those files over to my daughter's new Windows 11 laptop, it also shows the preview as corrupted so looks like it's a Windows 10 and 11 issue.

Having applied the conversion to "Camera Raw 14.0 and Later" all the previews look correct again in File Explorer.  Thanks for the tip!