Chapter 23. Animated GIFs

Users need no special software or plug-in. All they need is a browser that supports animation -- which is fortunately the overwhelming majority of browsers in use as of this writing.
GIF is the standard file format for the Web. Animated GIFs are not a unique file format in themselves, but merely take advantage of the full capabilities of the original GIF89a specification. Even if a browser cannot display all of its frames, the GIF will still be visible as a static image.
They're easy to create. There are scores of GIF animation tools available (some are built into larger web graphics applications), and they're simple to learn and use.
They require no server configuration. Because they are standard GIF files, you do not need to define a new file type on the server.
They use streaming technology. Users don't need to wait for the entire file to download to see something. Each frame displays as soon as it downloads.

The only drawbacks to animated GIFs are that they can contain no sound or interactivity (you can't make different parts respond to mouse actions), and they may cause some extra work for the user's hard disk to keep refreshing the images.

23.1. How They Work

Animated GIFs work a lot like traditional cell animation. The file contains a number of frames layered on top of each other. In simple animations, each frame is a complete scene. In more sophisticated animations, the first frame provides the background and subsequent frames just provide the changing portion of the image.

The GIF animation consists of a number of images and a set of instructions that specify the length of delay between frames, as well as other attributes like transparency and palettes.

Chapter 23. Animated GIFs

Contents:

23.1. How They Work