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.
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. JPEG compression uses a sophisticated algorithm that replaces every five pixels with a color value that is an average of those pixels. Images generated by a computer usually compress better in GIF format, while Images that originated as photographs retain more quality as JPEGs.