[gentoo-user] [OT?]: In search of a program to do different b/w dithering methods

Hi,

Happy New Year!!!

the programmable pocket calculator "DM42" offers OFFIMAGES,
which will be displayed, when the calculator is switched off.

The display is pure black and white.

For displaying (the illusion of) different shades of gray, one need
to convert the colored image into a so called "dithered" black and
white image (newspapers often use this trick).
Since -- in difference to the newspapers -- the pixels all have the
same size and can only be switched on or off only a few dithering
methods can be applied from which I want to choose the best suited
for a certain image.

The only problem: Which software can do this kind of conversion?

Thanks a lot for any help in advance!
Cheers
Meino