Last revision July 20, 2004
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When creating graphics to include in your Web pages, keep this consideration in mind: there is a trade off between quality of the graphic image when displayed, and size of the file, which directly relates to how long it takes to download.
On a direct network connection to a local server, you can expect to download images at speeds of 20 to 100 Kb per second. Direct network connections to more distant, or heavily loaded servers (at other institutions, for example) often proceed at only 5 to 20 Kb per second. If someone is logged into a network via modem connection, the best he can achieve is 1 to 5 Kb per second.
Use the minimum sized graphic that will do the job. In addition to simply using smaller images, you can reduce the size of graphics files by either using more compression (lower percent ratio) for JPEG images, or by reducing the color depth for GIF images (from 24 to 8 bits).
Provide thumbnails or indexes to large collections of graphics; then users can download and view only the ones they want.
Use the GIF format for line art and the JPEG format for photographic images. These formats can be displayed directly by all modern browsers. Other graphics formats often require the browser to start an auxiliary program in order to display the image. To help make it clear which format is being used for your images, save GIF image files with the suffix .gif as part of the filename, and save JPEG image files with the suffix .jpeg or .jpg as part of the filename.