1. In the Optimize palette, select GIF in the format menu. The palette changes; lots of options appear!
2. GIF images may have very limited amount of colors (up
to 256); the less colors contained in image, the smaller file we
get. First, let's choose a color reduction algorithm (movie).
There are 9 options in the menu; but unless you have a very specific
purpose, use one of the four upper options:
3. In the "Colors" field, define number of colors. As a rule, increasing this value results in better (but larger) image file. And vice versa.
4. With the "Web Snap" slider we can gradually replace "insecure" colors with web-safe ones (marked in the color table with tiny "diamond" symbol), thus making image more compatible.
5. Since GIF files contain a limited number of colors, we may want to imitate the missing colors with available ones using the dithering. From the "Dither" menu, we choose one of the algorithms for such imitation. The "Diffusion" method lets us adjust the amount of dither. With "Pattern" and "Noise" algorithms there is nothing to adjust.
6. Interlaced GIF files are loaded in a browser in a few passes (like the progressive JPEG's). In our case, however, this option enlarges the optimized file by 2 Kb, so we'd better deselect it.