GIF Info

Graphics Interchange Format (GIF) is a standard image file format that was proposed by a group of engineers from various software companies, and sponsored by Compuserve, back in 1987. This spec was called GIF87 or GIF87a.

In 1989, GIF was extended to support multiple image frames, positional overlays and cropping, index-key masking, and some user-interactive event handlers. This spec is referred to as GIF89a.

These enhancements provided support for transparent GIFs, which Netscape and other web browser vendors quickly adopted.

In 1996, Netscape added a LOOP extension that, combined with the GIF's new multi-frame extensions, provided GIF animation.

GIF animation provides many advantages:

Built-in streaming -- many other video formats must be entirely downloaded before they can be played; animated GIFs start playing as soon as data is received by the browser.
Transparency and overlays allow only portions of the image to be updated, making it easy for content authors to design optimized animated graphics.
Each frame can have its own delay, palette and interlace settings, allowing multi-resolution animation.

Legal Issue

GIF is dependent on LZW compression which is patented by Unisys. In 1995, Unisys began enforcing it's patent claim -- they settled with Compuserve, and provided a grandfather agreement with several major vendors using GIF prior to 1995.

However, Unisys claims that all other vendors creating GIF encoders (patent coverage of decoders is in dispute) must pay royalties on such products. This author was informed by Unisys that a royalty was required even if the GIF encoder was to be distributed for free.

As a result, Portable Network Graphics Format (PNG) was created as an alternative to GIF. It is royalty-free; however, it does not support animation.

GIF Specifications

Graphics Interchange Format (GIF 87)

Graphics Interchange Format (GIF 89a)

Excerpts from Royal Frazier's Animated GIF Tech Sheet

GIF References

Grafman's Animation Info

Netscape's GIF Animation Page