Web Design in a Nutshell, 3rd Edition

Chapter 29. GIF Format

GIF (Graphic Interchange Format) was the first graphic file type to be displayed by early web browsers, and it remains one of the most popular and versatile formats for distributing color images on the Web to this day. The GIF format was originally developed by CompuServe in 1987 to distribute images over their network to a variety of platforms (this is why you sometimes see GIFs referred to as “CompuServe GIF”).

GIF files have the following characteristics:

• They are indexed color images with a maximum of 8-bit color information (256 colors).

• They use LZW compression, which is a lossless compression algorithm.

• They may be interlaced, displaying in a number of passes on download.

• They may contain transparent areas.

• They may contain multiple images, allowing for simple animations.

Any image can be saved as a GIF, but the format is most appropriate for images with areas of flat, solid color, such as logos, icons, charts, and so on (see Figure 29-1). Even if the image contains some photographic elements, if the majority of the image is flat color, GIF is your best bet. GIF is also a good option if you want portions of your image to be transparent, and it’s your only option if you want the graphic to contain animation.

The GIF format is not particularly good for photographic images, because quality suffers as a result of the reduction to 256 colors and its compression scheme cannot work efficiently, resulting in larger files. Use JPEG for photos instead.

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