ANCIENT (ISH)
Halftoning is a process of depicting an image using dots on a page to depict varying grayscale tones.
The technique dates back to the mid-19th century when various people invented, patented, and fought over their methods of halftoning images for printing presses.
Halftoning is more famous, however, as a method for screen printing and laser printing where actual screens are used to create the dot patterns on top of the page. The screens can be rotated at various angles and overlapped to allow different colors to be printed with different patterns.
WHITE (and black) PEARL
This image I took of a building in the the gorgeous Pearl District of Portland is made black and white by testing every pixel's green value (scale 0-1) against a middle grey (0.5).
If the pixel's green is brighter than it, it's drawn as white. If not, it's black. This makes up the core of most dithering, where each pixel is compared against a value and drawn as one of two colors.
Instead of a flat value, though, they are compared against a pattern of values, which allows for various “gray” tones to appear in the image.