Ah, RAWTherapee! I’m supposed to be making a tutorial on how to use it for basic edits, but I just haven’t gotten a round tuit yet. 🙂
If you do need to export 16-bit TIFFs for any reason, just uncheck the “Uncompressed TIFF” option, and you’ll save a tidy little percentage of MB. Since TIFF compression is lossless, you don’t lose any info that way. It just requires a little more processor power when you open it.
Yep, the official GIMP software doesn’t support 16-bit editing yet. And no, it’s not really anything to do with file size, per se, it’s a matter of bit-depth. However, if you don’t mind trying “incomplete” software, GIMP 2.9 does support it! It’s slow, and might crash pretty easily, but it’s there. You can download it here: http://partha.com/downloads/Gimp-2.9.3-64bit.exe
As for TIFF vs. JPG, a JPG saved at a 100% compression ration should have about 99.9% of the quality of a TIFF at a huge savings in file size! (That’s my own statistic, don’t consider it official 🙂 ) In fact, some of the newer JPG codecs are considered lossless at 100%, but I don’t know of any software that uses that particular implementation/codec.
The only reason I can think of to use a 16-bit TIFF is to preserve maximum editability for other software. Like if you send a picture to a printer to be printed, and they determine that it’s too dark, so they brighten it a bit before printing. A 16-bit TIFF will do much better than your 8-bit JPG in that situation.
Thank you for asking that question! I learned a lot myself when researching this question, so it was good for me too!