Several variations - some variations include a compression algorithm to reduce the file size.
Not all graphics programs can read all of the variations
Common export format for scanners
Cannot view in web browser (without "plug-in")
.gif - Graphic Interchange File
One of the oldest formats
8-bit (256 color) images
No losses - every pixel is stored
Image is compressed, moderate/small file size
Can view in web browsers and most email programs
(Don't need to have separate graphics program to view)
.jpg - Joint Photographic Expert Group
24-bit (high-color) images
"Lossy" - pixels are "averaged" to reduce the amount of information that must be stored. The "quality" of the image (the amount of loss) can be adjusted from high (very little averaging) to low (a great deal of averaging).
Smallest file size
Can view in web browsers and most email programs
.bmp - MS Windows BitMaP
24-bit (high color) images
No losses - every pixel is stored.
Un-compressed
Largest file size
Cannot view in web browser (without "plug-in")
.png - portable network graphic
Modern version of gif
24-bit (high color) images
No loss
Moderate/large file size
Can view in newer web browsers (Netscape v6 & Microsoft IE v5) without a "plug-in" (but not in most email programs)
Save image in either .tif or .png for archival copy.
email: sturges@iastate.edu 
© 2001, Leroy D. Sturges