Dithering is an image display technique that is useful for overcoming limited display resources. The word dither refers to a random or semi-random perturbation of the pixel values.
Two applications of this techniques are particularly useful:
Low quantization display: When images are quantized to a few bits (e.g. 3) then only a limited number of graylevels are used in the display of the image. If the scene is smoothly shaded, then the image display will generate rather distinct boundaries around the edges of image regions when the original scene intensity moves from one quantization level to the next. To eliminate this effect, one dithering technique adds random noise (with a small range of values) to the input signal before quantization into the output range. This randomizes the quantization of the pixels at the original quantization boundary, and thus pixels make a more gradual transition from neighborhoods containing 100% of the first quantization level to neighborhoods containing 100% of the second quantization level.
Limited color display: When fewer colors are able to be displayed (e.g. 256) than are present in the input image (e.g. 24 bit color), then patterns of adjacent pixels are used to simulate the appearance of the unrepresented colors.
©2003 R. Fisher, S. Perkins,
A. Walker and E. Wolfart.