Lossy DNG converted files missing embedded jpeg previews since around version 13.0?

[Carlos_Oliveras]

I am using Lightroom Classic 13.3 and Windows 11. Let's say I convert a 22 MB raw file to lossy dng with Lightroom Classic using these settings:

• If compatibility is set to Camera Raw 15.3 or later, the resulting file will be around 5 MB and will not display the corresponding image thumbnail (just a generic icon) when viewed from Windows file explorer (tested both with Win11 and Win10). Also, it will not open in any image viewer.

• If compatibility is set to any other previous version (14.0 or older), then the resulting file will be around 10 MB, it will display the corresponding image thumbnail in Windows file explorer and will open in any image viewer (which will show the embedded jpeg preview in full size). This was the normal result for years, up until some version between 12.0 and 13.0 when (apparently) something changed.

I am not sure when this started happening exactly, but I think it was with some version between 12.0 and 13.0. I convert files to lossy dng on a regular basis, but I just noticed recently that the files I converted during the last months were abnormally smaller (if compared to the ones from previous years), missing their thumbnails (in Win file explorer) and impossible to open with any image viewer. After some investigation, I realized that, at some point, the conversions stopped including the Full Size preview (or so it seems), even though I always set it to Full size.

Am I missing something? Is it something on my end? (I don't think so because I have done tests on two computers, but... who knows). If more info is needed, please let me know.

Thanks if anyone can comment on this.

[Victoria Bampton LR Queen · Accepted solution]

You're not missing anything. In 13.0, October 2023, Lossy DNG was changed to use JPEG XL compression instead of JPEG. The space savings are huge, as you've noted, because the compression is much more efficient. The downside is that most programs haven't been updated to understand the new compression yet.

[Carlos_Oliveras]

Thanks Victoria. Because of some things that I read during my "investigation", it did cross my mind that this move to JXL might have something to do (I don't know the full details on it, but I did read Rikk Flohr saying something about JXL and DNGs created with Panorama photo merge). But since the embedded preview in regular DNG conversions (not lossy) are not affected by this problem feature, I (wrongly) assumed that there should be another explanation.

Apparently Microsoft (I'm on Windows) hasn't yet provided compatibility/support/codecs or whatever it is needed for JXL... and while they say that there are third party solutions, they being Microsoft can't recommend any software in particular. So, it's like you say - it looks like software developers haven't caught up with this newer technology.

So, if this is "a feature not a bug", that's it 😣 I just wish Adobe hadn't adopted this technology so early. For the past few months I converted a ton of files to lossy DNG without realising that from a certain version onwards, the resulting files are not visible anymore from Windows File Explorer and I can't open the previews either with any of my image viewers.

Now I need to work with those hundreds of files, and it's like I am blind because I have absolutely no idea which file is which unless I open Lightroom Classic or Bridge everytime, which is a pain (I have been converting to lossy dng for years, that's why I didn't check the thumbnails previews, I wasn't expecting something like this). I don't have the original raw files anymore. And while maybe I could re-convert the lossy DNG files this time using an older Camera Raw compatibility setting (I assume then the thumbnail would be visible), I guess that's not a good idea since that would apply another "layer" of lossy conversion.

😞I'll look for third party solutions because this is a huge pain...

Thanks again Victoria for your quick and kind help 👍🙏