Web Design in a Nutshell

When to Use GIFs

GIF is a versatile format for condensing color images for use on the Web. It is particularly well-suited for any image with areas of flat color, such as logos, line art, icons, cartoon-like illustrations, etc. It will compress them cleanly (since it is a lossless compression) and efficiently (LZW compression looks for repetition of pixel colors).

You will also need to use GIF format if you want a portion of the image to be transparent, since it is the only format universally supported by browsers. PNG files can contain transparency information (actually, in a more sophisticated way than GIF), but as of this writing, browser support is too spotty to use them confidently.

GIF is also a good option for adding simple animation to your page without relying on plug-in technology, Java programming, or server-intensive methods. Most browsers display an animated GIF as easily as any other GIF. See Chapter 18, for more information on GIF animation.

GIFs are not particularly good for photographic images. With the 8-bit limit, true color information is lost and the subtle gradations of tone become pixilated when the image is reduced to 256 colors. The quality of the image may be greatly reduced. In addition, GIF is not able to condense photo-realistic image content efficiently.

In many cases (especially for very small images), GIF will work just fine for all image types, but you will get much better image quality and smaller file sizes if you save photographs and continuous-tone ...