One more thing about Darktable and processing negatives..

I forgot to mention that Darktable does actually come with a module that inverts negative images automatically.  To do this you need to feed it a small sample of unexposed but developed film (e.g. the borders of a negative, or the blank frame at the start / end of the roll); it will then - theoretically - invert and neutralise that colour tint.  I say theoretically because I've never got it to work to my satisfaction; hence my method (which also allows processing in batches).