Optimization: GIF Format (Video Included)

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:

- Web uses only web-safe colors, that must look similarly on any monitor in the world. Sounds good, but the small amount of available colors often causes a loss of quality. Use it for clipart, buttons and similar stuff.
- Perceptual, Selective and Adaptive give rather good and very similar results. Although, Selective is a default (and supposedly the best) algorithm, let's choose the Perceptual at this time.

3. Now let's define the amount of colors in the Colors field. In the movie I select one of standard values in menu, but you can type any number up to 256.

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. A strange compromise, in my opinion.

5. Since GIF files contain a limited number of colors, we may want to imitate the missing colors with available ones using the Dither. In the Dither menu we choose algorithm of such "imitation". The algorithm Diffusion allows us to adjust the amount of dither with the Dither slider. 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.

While changing the settings, look at the Color Table palette. It displays all the colors of the optimized GIF image. Every change makes it to re-builds the color scheme. Also, this palette allows us to manage colors at will. Although as a rule, manual handling is not necessary, you may try it just to see how changes in the Color Table affect the image quality.

7. For example, click the "new" button to add the current foreground color to the color table.

8. To delete a color, drag it onto the "trash" button.

Note that you are not obliged to use all the menus and gadgets in this palette. In practice, you usually set only an amount of colors. All the rest matters, but not so much.