The sluggish behaviour of the AppImage is not normal… could you please try the following:
- install
bsdtar - create a folder where to extract the AppImage contents, something like
mkdir RawTherapee.AppDir - go into this folder and extract the AppImage contents:
cd RawTherapee.AppDir
bsdtar xfp FULL_NAME_OF_THE_RT_APPIMAGE - the run RT like this:
./AppRun
Is this faster? If yes, the slowness might be due to some repeated access to some files in the AppImage bundle, which AFAIK is a compresse archive that gets deflated on-the-fly.