Simulating more colors and shades in a palette. In a monochrome system that displays or prints only black and white, shades of grays can be simulated by creating varying patterns of black dots. This is how halftones are created in a monochrome printer.
In color systems, additional colors can be simulated by varying patterns of dots of existing colors. Dithering cannot produce the exact same results as having the necessary color depth (levels of gray or colors), but it can make shaded drawings and photographs appear much more realistic.
Dithering is also used to create a wide variety of patterns for use as backgrounds, fills and shading as well as for creating anti-aliasing effects.
Dithering a Color Image
When there aren't enough colors in a display system to render an image properly, an infinite palette can be created by dithering. Quite often, a 24-bit color image is dithered to 256 colors. The right side is a magnification of the white box on the left.
Dithering Text
Text is also dithered. Notice how much softer the word DATABASE is at the top of this example, compared with the undithered word below it. The magnified view shows where lighter blue pixels filled in for the curves. When dithering is performed against the edges of an image, it is called "anti-aliasing."