LrC 12.3 and newer: HDR DNGs cannot be open by image viewer (Windows)

[Karsten.G]

LrC 12.3 seems to have changed the format of DNG files for HDR files created inside LrC.

Neither my favorite app IrfanView nor eg Windows PhotoViewer can open these files.
Windows file explorer does not display an image thumbnail but only the file type.

DNG files created by LrC Noise Reduction are not affected, they can still be opened by other programs.

Is this change intended behavior? 
If so, is there any reference that could be used by 3rd party to update their viewer apps?

[JohanElzenga · Accepted solution]

Yes, this is not a bug, but as designed. Lightroom Classic 13 uses a new compression method that makes these files a lot smaller. It's in the "what's new?" documentation.

[Karsten.G]

@JohanElzenga This was my first thought as well. But looking at my files, I can reproduce that "unreadable" HDR DNG files already started with LrC 12.3. Also, the problem does not exist with the DNGs created by AI Noise Reduction.

[JohanElzenga · Accepted solution]

AFAIK, nothing changed in version 12.3. Remember that most viewers cannot view the raw or linear image data. What they show you is the embedded preview, so maybe there was a change in that.