How can I convert a JPEG photo to black and white (not grayscale) image like output of a FAX scanner, by ImageMagick?
According to this forum post:
However, if you want two colors only (black and white), then you need to threshold. For example, to select the color where above will be white and below will be black.
where xx is in range 0-100 (for percent).
Dithering is clearer and more fax-like than a threshold cutoff:
For a less contrasty but more information-preserving kind of dithering, use: