Dithering is the attempt by a computer program to approximate a color from a mixture of other colors when the required color is not available. Dithering can occur when reducing the nubmer of colors of an image, transforming art to Web safe color palette, or displaying a color that a browser on an operating system can't support. In such cases, the requested color is simulated with an approximation composed of two or more other colors it can produce. The result may or may not be acceptable to the graphic designer. The image may also appear somewhat grainy since it's composed of different pixel intensities rather than a single intensity over the colored space.
Pattern dithering is most useful in filling a larger area with a desired color.
Diffusion dithering works well for continuous tone pictures. Your usercode and password are required. Then just upload any file from your home computer to your home directory under UNIX, or download any file from UNIX to your home computer. Refer to Web Help for more info. After I upload my html file, I still need to open the file up for the Web.