You cannot write a camera raw file in Natron, since Natron is not a camera. What exactly do you want to achieve that way? Do you want to re-apply the camera defects, re-mosaic the image, and then write it so that the next software thinks it comes directly from the camera?
There’s no such thing in Natron, sorry.
In the meantime, you can:
- get quasi-lossless compression with EXR using either dwaa or dwab
- write 16-bit PNGs
- write 10, 12 or 16-bit DPX
- write any image format mentionned in the documentation for the WriteOIIO node: WriteOIIO node — Natron 2.3.16 documentation
Next version of Natron will also support HEIF/HEIC: High Efficiency Image File Format — Wikipédia