It's the tool for postprocess camera RAW files to several formats. Raw converter uses RawPy library
rawproc /home/user/photo/* --res-dir /home/user/final_photo --out-type .jpeg
You can get thumbnail for more speed rendering. But on some cameras it don't work and may return different thumbnails for different cameras.
rawproc /home/user/photo/some_img.CR2 --res-dir /home/user/final_photo --get-thumb
By default --out-type is .jpeg and --res-dir is same dir with input file
pip3 install rawproc