- Gimp doesn't know how to save as .pbm !!
  So save as .pgm (gray) and convert with:
  pgmtopbm -thres < in.pgm > out.pbm

  Or, including flipping and margins:
  pgmtopbm -thres < in.pgm | pnmflip -cw | ../dypbmfixmargins > out.pbm

  This allows us to have light-gray borders that disappear when printing.

- Font handling by Gimp is weird (Gimp 2.2 tested): non-aliased
  black/white font rendering changes when the text box is moved around!

  Further, "normal" hinting usually works best, but for some fonts (and
  on some positions!) "autohinter" is better.
