GIF images can not have more than 256 colors. The best thing about GIFs is that you can achieve really small graphic files by instructing your image editing program to use less than 256 colors. Many computer generated images look just as good using 24 colors as they do using 256. You can even get away with 4 or 8 colors on very simple logos. The less colors you use, the smaller your files will be.

The image to the right had used 133 colors when it was created in Photoshop. By converting it from RGB to indexed 12 color (By typing "12" in the "other" box under "Mode") we were able to compress it without loosing noticeable quality. This brought the file size down to 6 Kilobytes. --->>

You should experiment with the amount of colors since each image will have different requirements. Very simple images like this boat use minimal colors. With your images, try using 8 or 12 colors first. If the quality difference is undesirable add more colors until you find the lowest setting that still looks good. It is best to add colors in increments of 4 or 8.

GIF compression also works with vertical gradations of color. The image to the right has vertical gradations in the sky and the sea. If we were to save this image sideways, the file size would be 1000 bytes larger. --->>

JPEGs

JPEGs compression is capable of 24 bit color (millions of colors) and is better at displaying photographs. Photographs are often more complex than computer-generated art. For instance, a photograph of a tree can have hundreds of shades of green in it. GIF compression will attempt to "dither" those colors down to just a few shades. This results in a "banding" effect which degrades the look of the image. JPEG compression uses a sophisticated algorithm that replaces every five pixels with a color value that is an average of those pixels.

A Very Handy Trick: If you use Photoshop, you will see a reduction in file size if you turn off "Previews" in the: FILE >> PREFERENCES >> GENERAL >> MORE... window (as shown below in Photoshop 3.0).

Summary: Images generated by a computer usually compress better in GIF format, while Images that originated as photographs retain more quality as JPEGs.