I like the new option of "Lossy DNG" to save some disk space on some of my files. Now I want to convert a part of my existing Lossless DNGs to Lossy DNGs. Lightroom can do that for a couple, but It does not seem to do a good job on thousands (slow I/O, only 50% CPU, complaints about metadata conflicts).

Is there a batch-tool other then Lightroom to convert a bulk of DNGs suitable for this task?

PS: No discussion about Lossy DNG, please. I am aware of the risks and handle them.

  • \$\begingroup\$ @dpollitt: Photoshop can not save DNGs. DNGs are raw (and Lossy DNGs are "almost" raw). \$\endgroup\$
    – towi
    Commented Feb 11, 2013 at 9:40
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    \$\begingroup\$ I suspect that other tools haven't caught up yet, I haven't found any. It's also still likely to be a computationally expensive process if there's any reasonable processing happening to the images to maximize output quality while compressing. Frankly, I'd just buy some external drives and keep them as is as it would probably take a lot less time and thus be cheaper (your time isn't free). \$\endgroup\$
    – Joanne C
    Commented Feb 11, 2013 at 13:24
  • \$\begingroup\$ You can probably fix the metadata conflicts by saying Cmd/Ctrl-S on all the photos you want to convert first. That forces LR's copy of the metadata to overwrite the XMP in the DNG files. \$\endgroup\$ Commented Feb 12, 2013 at 4:05
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    \$\begingroup\$ You tried Adobe DNG Converter? \$\endgroup\$ Commented Feb 14, 2013 at 9:01
  • \$\begingroup\$ @MarcinWolny: For DNG to DNG...? No, I didn't. Ok, I will take a look. \$\endgroup\$
    – towi
    Commented Feb 14, 2013 at 13:54

1 Answer 1


Yes, the Adobe DNG Converter will let you bulk convert Lossless DNGs to Lossy DNGs. In fact, I once wrote a script which scoured my entire library of DNGs to find all of my uncompressed DNGs and converted them to (lossless) compressed DNGs. Their DNG Converter is free and easy to run on a system which doesn't have Lightroom to bulk convert mass quantities of DNGs.

However, I usually do this within Lightroom, since it allows me to automatically add the converted files back into the catalog. All of my 2nd tier photos (not bad enough to be deleted, but which didn't make the final cut) get converted to a lossy DNG format. In fact, in most cases I convert them to reduced-resolution lossy DNG files (between 2mp and 6mp, depending on whether or not I think there is a chance of ever printing above 5x7"). I use one of my export presets to export the selected photographs to these reduced-resolution lossy DNG files (in a subdirectory of the original, named LossyDNGs) and then mark them as rejected. Once the export is complete, I delete all the rejected photographs.

This way, all of the photographs are still in my library, but most of them take up significantly less space, yet still have much of the flexibility of RAW files.

  • \$\begingroup\$ Good to know! Does this DNG Converter apply Lightroom's edit list, or does it just convert the original, unedited photo? \$\endgroup\$
    – Jerry101
    Commented Jul 28, 2018 at 23:09

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