Original Converted to Black-and-White
Increase the contrast in black-and-white images to produce a stronger, more graphic picture. If the original is in color, first convert to black-and-white, then increase the contrast until you achieve the desired effect. This technique works well with silhouettes with clear outlines, and with objects with geometrical shapes or strong patterns.
From How To Photograph Absolutely Everything: Successful Pictures From Your Digital Camera by Tom Ang (DK Publishing, 2007, $40)_