For those who don’t know, you can use the gratis Adobe DNG converter as a poor man’s camera raw processor. It turns out that the DNG converter reads ACR settings from an xmp sidecar when generating the (full-size) jpeg preview for the DNG. Therefore, it’s enough to “craft” the proper xmp sidecar and then extract the embedded jpeg to sort of emulate what ACR would do (actually, I assume it’s accurate, since I don’t have ACR/Lightroom so I cannot cross-check).
I have a script for doing that which I sometimes use for curiosity. I’m attaching it here, I don’t think it violates any license. It assumes you have dcraw installed and the Adobe DNG converter working under wine (though it shouldn’t be too hard to adapt to other scenarios).
adng.py (6.7 KB)
Example usage (use adng.py --help for the full set of options):
$ adng.py -j -o blue_horse_default.jpg blue_horse.nef
$ adng.py -j -o blue_horse_clarity100.jpg blue_horse.nef --clarity 100
Hope this helps