What is Dithering?

Dithering is the most common means of reducing the color range of images down to the 256 (or fewer) colors seen in 8-bit GIF images. Most images are dithered in a diffusion or randomized pattern to diminish the harsh transition from one color to another. But dithering also reduces the overall sharpness of an image, and it often introduces a noticeable grainy pattern in the image. This loss of image detail is especially apparent when full-color photos are dithered down to the 216-color browser-safe palette.