Chapter 19. GIF Format
Contents:
GIF87a Versus GIF89a
8-Bit Indexed Color
GIF Compression
When to Use GIFs
Tools Overview
Interlacing
Transparency
Minimizing GIF File Sizes
GIF (Graphic Interchange Format) was the first graphic file type to be displayed by early web browsers, and it remains the most popular and versatile format for distributing color images on the Web to this day. Any image can be saved as a GIF, but they excel at condensing graphical images with areas of flat color.
GIFs are completely platform-independent, meaning a GIF created on any platform can be viewed and edited on any other platform. They were originally developed by CompuServe to distribute images over their network to a variety of platforms (this is why you sometimes see GIFs referred to as "CompuServe GIF").
It is also the only graphic file format that is universally supported by all graphical browsers, regardless of version. If you want to be absolutely sure everyone will see your graphic, make it a GIF.
19.1. GIF87a Versus GIF89a
There are technically two types of GIF file: GIF87a and the newer, improved GIF89a. Both are fully supported on most browsers, and both use .gif as their file name suffix.
GIF87a is the original format for indexed color images. It uses LZW compression and has the option of being interlaced.
GIF89a is the same, but also includes transparency and animation capabilities (animation is discussed in Chapter 23, "Animated GIFs"). If you want to add these features to your graphic, you'll need to create the graphic with a tool that supports the GIF89a format. These features have become so popular with web developers that this format has become thede facto standard on the Web today. Detailed descriptions of each feature appear in the following sections of this chapter.
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| III. Graphics |  | 19.2. 8-Bit Indexed Color |
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