Once you compress an image with JPEG, data is lost and can never be recovered, so always save an uncompressed original file of graphics. A new form of JPEG file called progressive JPEG' gives JPEG graphics the same gradually-built display seen in interlaced GIFs, but most image editors do not yet support progressive JPEG files. Like interlaced GIFs, progressive JPEG images usually take longer to load onto the page than standard JPEGs, but they do offer readers a quicker preview'. Basic diagrams also work well on the computer screen if they are carefully designed to match the grid of pixels on the screen. Graphics built with straight horizontal or vertical lines, or diagonal lines at 45-degree angles, work best for the screen.
Complex icons are hard to interpret, and look mushy and confusing on the screen.
Keep your icons and navigation graphics as simple as possible. With screen legibility a high priority, the only alteration recommended to the standard web page is shifting the page background from grey to white. The legibility of type on the computer screen is already compromised by its low resolution. Avoid using background images if you do not have professional graphic design training or experience in constructing complex graphic communications the chances of making a functional or aesthetic error are high. Image maps have become features of most professionally designed web sites because they offer an effective combination of visual appeal and, when used properly, space-efficient functionality.