As the number of bits used increased, the number of possible colors increases. For example, a 1-bit image can display only two colors, Black or White. An 8-bit image can display up to 256 colors. A 24-bit image can display up to 16.7 million colors. The downside is, that as the number of bits goes up, the amount of space the file takes up also increase.
Larger files take longer to load when viewed on Web pages.
A good compromise is to create images that require no more than 8-bit to describe their color. This allows for 256 individual colors and creates a moderate file size. In addition, many computers, especially some IBM compatibles, are only capable of displaying 256 colors. The easiest way to create an 8-bit images is to convert it to a GIF file format. Several freeware and shareware converters exist for both Macintosh and Windows machines that do the conversion for you.