Once having decided image size, the next choice to make is that of image format. Creating GIF images requires the most balancing of mutually exclusive factors, namely number of colors, how they are chosen, and how to transform the original image's colors into the final colors. If you are using PaintShop Pro, you can have it count the number of colors used by the image. Anything less than 256 should be saved in GIF no matter what the image size. You can choose any number between 2 and 256.
More colors means better image fidelity, but also means a larger image file.
The next choice is which colors. The most common choices are Optimal and Web-safe. A web-safe palette uses colors that are guaranteed to look predictably in anyone's web browser. An optimal palette produces the smallest image files, while a web-safe palette is less likely to produce surprising output when viewed on another computer. Finally, you must choose which technique is used to transform the colors in your image into the colors in the GIF representation.