Dithering is used in computer graphics to create additional colors and shades from an existing palette by interspersing pixels of different colours. On a monochrome display, areas of grey are created by varying the proportion of black and white pixels. In colour displays and printers, colours and textures are created by varying the proportions of existing colours. The different colours can either be distributed randomly or regularly. The higher the resolution of the display, the smoother the dithered colour will appear to the eye.
Dithering doesn't reduce resolution. There are three types: regular dithering which uses a very regular predefined pattern; random dither where the pattern is a random noise; and pseudo random dither which uses a very large, very regular, predefined pattern.
Dithering is used to create patterns for use as backgrounds, fills and shading, as well as for creating halftones for printing. When used for printing is it very sensitive to paper properties. Dithering can be combined with rasterising. It is not related to anti-aliasing.