Printing in black and white without intermediate greys

Solution 1:

To convert easily any image in Black & White (no gray):

• Open the file in Preview
• Choose "Save As…" (Visible in the File menu, while holding the Alt key in Mountain Lion)
• In the save dialog, choose the PDF file format
• Still in the dialog, apply Quartz filter: "Black & White"

EDIT: You can convert to black & white with dithering using The Gimp (free & open-source):

• Open the image using The Gimp
• Select menu item Image -> Mode -> Indexed…

• On the window that opens:

  • Select the Black & White palette
  • Select a dithering mode (I chose Floyd-Steinberg)

You can also use Photoshop using the same technique. However, Photoshop is expensive.

Finally, command-line solutions exist: convert (part of the imagemagick package), or gm (part of the graphicsmagick package).