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.
