http://www.lib.rochester.edu/multimed/image.htm

GIF

GIF stands for Graphic Interchange Format and it is a standard format for images that was developed by
CompuServe to be a device- independent method of storing pictures. GIF allows high-quality, high resolution
graphics to be displayed on a variety of graphics hardware and is intended as an exchange and display
mechanism for graphic images.

GIF is reasonably well matched to inexpensive computer displays, since it can only store 8 bits/pixel (256 or
fewer colors) and most PCs can't display more than 256 distinct colors at once. GIF does well on images with
only a few distinct colors, such as line drawings and simple cartoons. A GIF picture file has an extension .gif.

     Animated GIFs

     An animated GIF is created using GIF89a format. It contains several frames, i.e. a sequence of GIF
     images, and can be set up to display the images one after another or in a loop, so you can see the
     images moving. An animated GIF picture has the same file extension .gif as a still GIF picture. What
     makes the Animated GIF special is that you don't have to install other Helper Applications in your
     web browser, Netscape 2.0 or higher displays Animated GIFs. Here is an example of Animated GIF.

     Transparent GIF

     A Transparent GIF is a GIF image with a transparent background. When you view a transparent
     image on your web browser, your browser's background shows through the image's background, in
     whatever color you set up as your default display color, or the page author set up as the page's
     background color. The Transparent GIF format allows a web browser to display any shapes of images,
     not just square or rectangular shape that you can create using most graphic creating tools. A
     Transparent GIF file has the same file extension .gif as a regular GIF format.

     See Transparent GIFs for more information.



-------------

JPEG
24 bits/pixel


http://www.whatis.com/ff.htm


http://www.whatis.com/jpeg.htm

JPEG (Joint Photographic Experts Group) 

A JPEG (pronounced JAY-peg) is a graphic image created by choosing from a range of
compression qualities (actually, from one of a suite of compression algorithms). When you
create a JPEG or convert an image from another format to a JPEG, you are asked to specify
the quality of image you want. Since the highest quality results in the largest file, you can make
a trade-off between image quality and file size. Formally, the JPEG file format is ISO
standard 10918. The JPEG scheme includes 29 distinct coding processes although a JPEG
implementor may not use them all. 

Along with the Graphic Interchange Format (GIF) file, the JPEG is a file type supported by the World Wide
Web protocol, usually with the file suffix of ".jpg". You can create a progressive JPEG that is similar to an
interlaced GIF. 

Assistance was provided by Seth Goldberg.
A source: C. Wayne Brown and Barry J. Shepherd, Graphics File Formats Reference and Guide, Manning (1995).