Using GIF Compression
The GIF (Graphics Interchange Format) was developed by CompuServe more than ten years ago to help keep the size of online files small. The current incarnation of GIF is GIF89A, which includes the ability to have transparent areas (which can be set in any software that creates GIF89A images).
The major limitation of the GIF format is that it restricts graphics to a set number of colors, never more than 256. When cross-platform documents are being created, there are really only 216 colors that can be used (that's the number of colors that are the same between both Macintosh and Windows platforms). However, it is this limitation that allows the GIF format to be rather flexible. Instead of losing image data as with JPEG, GIF images retain each pixel's "difference" in color, but the color itself is often changed in order to fall within the limitations of the number of colors used. For monochrome images or images with only a few colors, GIF is an excellent choice.
To set Acrobat Distiller to maintain GIF image compression:
Choose Job Options from the Settings menu (Figure 3).
Choose Job Options from the Settings menu.
Click on the Compression tab in the Job Options dialog box (Figure 4).
Click on the Compression tab to view the different graphics compression options. Uncheck the Automatic and Manual compression checkboxes.
Uncheck the Average Downsampling and Compression checkboxes.
Click the OK button.
In order to use images with GIF compression, the images must be saved as GIF images before they are placed into the application that creates the PDF. Acrobat has no way to convert other image types to the GIF format.