Keeping file size under control ? crop & export to DNG?

Ladies & gents,

I’d like to share a problem with you guys and try to find a viable strategy to keep file size to a manageable limit.

I’m digitizing using an olympus E-M5 mk II with a m.zuiko 60mm using the High Resolution mode. I’m doing this not mainly for resolution, as I think the gain is a bit exaggerated for my typical export & printing needs but also for better color accuracy and a reportedly slightly wider dynamic range so that I don’t have to hdr or stack.

The problem is that each file gets to a whopping 100MB. It’s heavy on storage and computing time. I frame my shots excluding about 10% of vertical & horizontal borders as to exclude extreme corner sharpness.
I was exploring the idea of cropping (following the red line) in lightroom and exporting to another file format and then discard the original files. From that point I’d carry on with NLP.

Testing with DNG & TIFFs, a 100MB ORW file of 9216x 6912 px becomes a 7750x5073 px file weighing :
45 MB with DNG
76 MB with TIFF sRGB 16bits ZIP compression

So I’d like to go with the DNG but I’m concerned about what’s stored in the file.
Is it only an actual 1:1 crop and bit depth is preserved / is lightroom altering the data on export ? Is NLP handling DNG just like any other file ?

Thanks in advance if anybody knows,


Oh and of note, I noted that lightroom export to dng didn’t take Transform Horizontal flip into account, so a good thing to keep in mind is doing all the cropping & export before any actual work.