On the other hand the GIFs produced without doing anything have a very
bad resolution (e.g. 768x662 pixel). The workaround here is to resize
the graphic window to a larger size ("set window/size=2" would result in
1141x984).
The "ferret -gif" command should work fine with window resizing. Check out
the details at "Ch1 Sec2.2. Unix command line switches" of the on-line Users'
Guide. Note that when generating images in this mode you need to resize the
window BEFORE you issue the plotting commands.
That worked! The important point was to resize right at the beginning
using "set window/clear/size=2".