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Types of Dithering

Diffusion, pattern, and noise are the three types of dithering available in Save for Web. Dithering is used to perceptually ease the transition between two colors by arranging pixels to create the appearance of intermediate colors. Much the way that a photograph in a newspaper creates the illusion of numerous shades of gray using only black ink, so this dithering creates the perception of several colors or shades when only two colors of pixels are being used. Diffusion dither, when used with either GIF or PNG-8, allows control of how much dithering is applied. The Dither slider in the Settings area ranges from 0% to 100%. Figure 22.24 and Figure 22.25 show the difference between 50% and 100% dither in close-up, respectively, and Figure 22.26 and Figure 22.27 show the effects as they would be viewed on the Web.

Figure 22.24. Diffusion dither at 50% is magnified to a zoom level of 250%.



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