Author Topic: Dark frame subtraction with lossless DNG format  (Read 1880 times)


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Dark frame subtraction with lossless DNG format
« on: April 26, 2018, 10:14:02 AM »
I'm having problems with dark frame subtraction and the lossless dng file format.
I wonder if any of you have the same experience or that it is the software(RawTherapee) I use ?

I find out that with adobe DNG converter, you can convert normal DNG files to Lossless DNG files.
So I'm testing with converting old DNG's from raw recordings I did years ago to lossless DNG format.
But for Iso 6400 and sometimes ISO 3200 I made dark frames. which work fine with the none lossless DNG files.
But once converted to lossless, the dark frame subtraction doesn't work (picture gets really dark and the remaining highlights look posterized).
I've also tried converting the dark frames to lossless DNG file format, so both files have the same format, but this didn't gave other results.

The lossless file format from adobe DNG converter should be the same LJ92 compression ML uses.
Did maybe any of you use full res silent picture with lossless option and tried dark frame subtraction with it ?


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Re: Dark frame subtraction with lossless DNG format
« Reply #1 on: April 27, 2018, 01:43:14 PM »
Hm. This is weird. The only cases I can think of, if applied compression is lossy or if black/white level is inserted by adobe is different or bit depth is different (last one not likely).