I prepared a Ubuntu script using:

Sane, Gimp 2.6, Convert, Tesserat, gedit

Gimp 2.6 has its own script, but I found that it was very difficult and time consuming to correct errors. Gimp item is therefore manual. The script opens it automatically and all I have to do is mode / index / black and white/ and be sure it is saved a jpeg again (grey scale) and close gimp again.

I use gedit to show the result.

If you are interested, please e-mail me at aguilla1@telusplanet.net