A Complete Guide to Web Design

280 Chapter 14 – GIF Format

Minimizing GIF File Sizes

Web Design in a Nutshell, eMatter Edition

3. Convert the image to Indexed Color again, only this time, choose an Exact
   palette that reduces the number of colors in the Color Table from 216 to just
   the number of colors that are actually used. This can significantly reduce file
   size, depending on the image.
   When converting to Indexed Color, Photoshop limits your control over dithering
   to either None (no dithering) or Diffusion (dithering). This “on” or “off” approach
   to dithering doesn’t allow you as much opportunity to reduce file size as is
   possible with other tools (discussed below).

Macromedia Fireworks 1.0

In Fireworks, optimization controls are accessed via the Export Preview dialog box

(FileÝExport) shown in Figure 14-10. It provides a number of palette options to

choose from, and once in a given palette, the actual number of colors may be

reduced to reduce the size of the file. There is also a sliding scale for precisely

controlling the amount of dithering. Higher percentages allow for more dithering.

When you reduce the dithering amount, areas of the image simplify and LZW

compression can work more efficiently (resulting in smaller files).

At very low dithering rates, your image may look posterized. If this is not the

effect you want, experiment with the point at which you get the greatest reduc-

tion in file size while maintaining image quality. This point depends on the

content of the image—dithering is most acceptable in photographic images and

least acceptable in areas of flat color.

The Export Preview allows you to view up to four different versions side-by-side,

along with their corresponding file sizes and typical download times, so you can

Figure 14-10: Macromedia Fireworks’ Export Preview dialog box