Dithering

Dithering is a type of half tone thresholding where greyscale (or RGB channel) intensity is converted into a local density of binary pixels. This is ideal for rendering images in devices with a binary output such as printers (greyscale) or with a small number of colours (colour dithering). The following methods have been implemented (there are several more):

• Floyd-Steinberg
• Atkinson
• Jarvis-Judice-Ninke
• Stucki
• Bayer_2x2
• Bayer_4x4
• Bayer_8x8
• Clustered_4x4
• Random

Here is a good text explaining various dithering algorithm.