Graphic Formats
The Yale Web Style Guide
shows the difference between one-bit,
8-bit and 24 bit colour displays.
GIF
The GIF format is the most common on the Web. All graphical web browsers can read GIF
images. GIFs are small files restricted to 256 colours. They are slightly compressed, but no image
quality is lost through the compression. GIFs are used for icons, buttons, and simple line
diagrams.
GIFs can give the appearance of having more than 256 colours by carrying their own
colour pallets with them
GIFs can also be used for simple animations: 
and one colour in a GIF can be chosen to be transparent, so that the background of the
page shows through.
JPEG
JPEG images are used for large, photo-quality pictures. JPEG pictures can be compressed much further than GIF,
but with some loss of quality. JPEG files are generally larger than GIFs.
JPEG Vs
GIF images
Borrowing Graphics
It is possible to "borrow" images from web pages.
On a PC, point to the graphic you wish to borrow, and
click the right mouse button. A pop-up menu will appear which will allow you to save or
copy the graphic. On a Macintosh,
point to the picture and click and hold the mouse button. A pop up menu will appear,
allowing you to save the image to disk. On more recent Macs, those running system 7.5 or
later, it is possible to copy images directly, or even to drag them from one application
to another.
