Dithering
Dithering is approximation or reconciliation of colors between an image palette and the system palette. The dithering process works by placing two colors from the system’s palette next to each other in order to trick the eye into seeing a third color that is desired but not part of the palette. Dithering makes it possible to display images that contain more colors than the system displaying them can support.
When a web browser encounters an image that contains colors not supported by the current monitor setting, the browser will automatically use dithering to try to approximate the correct colors in the image. Unfortunately, dithering can alter the image’s appearance in ways you might not want. In particular, a high-color image such as a photo can appear grainy when displayed on a computer that supports only 256 colors.
When you create web images using a graphics-editing program, you can specify whether the image should use dithering or whether the graphics application should change the image color to the closest Web-safe colors. If you use only colors in the safe 216-color palette that can be displayed on both Netscape and Internet Explorer browsers (i.e., web-safe colors), then your images will not dither when viewed on any browser. However, using only web safe colors severely limits the range of colors and types of images you can use on your pages, and is rarely an option for photographic images. The consensus among designer today is that you should use web-safe colors when ever possible.
