Unisys might want five kilobucks from you. If the program you used to create GIFs for your Web site employs an unlicensed copy of the Lempel-Ziv-Welch compression algorithm, then Unisys says you are guilty of "contributory infringement" on its patent for the algorithm. Think of it as being an accessory after the crime.

And note that the US$5,000 Unisys wants is only if you aren't posting such GIFs on a commercial Web site and don't require a password. If your site is commercial then you need to talk to Unisys -- and start saving up those nickels and dimes.

Developer News spoke to Oliver Picher, spokesman for Unisys. Picher is in charge of fielding questions about the LZW patent and is a friendly fellow who's clearly fascinated with the ramifications of patents in the real world. We posed a question to him: "Let's say I have a Web site and someone sends me a file that was compressed using an unlicensed copy of the LZW algorithm -- a GIF for example -- and all I do is allow others to download that file from my site. In other words, I neither compress nor decompress the file; I simply make it available. Do I need a license from Unisys?"

Picher laughed, "Great question!" He explained that such an action is considered "contributory infringement" because you're helping an infringer. He went on to downplay the official Unisys position by observing, "If you ask a highway patrolman if you can speed he'll say no, even though the odds are you won't get caught." Unisys is not out searching for violators of its patent, Picher said. He added that most programs producing GIFs are licensed, so there's usually no problem.

Check that old code

If you're involved in Web development this situation can directly affect you because GIFs are so ubiquitous. But even if you're not a Web developer, LZW has been around for a long time and was long thought to be in the public domain. It may even be buried in some code you're maintaining.

So if you create or distribute software that uses LZW compression technology in any way, you must deal with the ramifications of the Unisys patent. As a recipient, user, or distributor of hardware or software products containing LZW compression capability, Unisys cautions you to make sure that you are lawfully acquiring and distributing licensed LZW software.

In 1983 Sperry filed for a patent on the LZW technique. Terry A. Welch described the LZW algorithm in the June 1984 issue of IEEE Computer Magazine, but he did not mention that the algorithm had a patent pending. In 1985 the patent was granted.

Thanks to Welch's article, LZW became a popular technique for data compression. CompuServe used the algorithm in the design of GIF files, and the GIF format grew in popularity when, oblivious to the patent, CompuServe released GIF as a free and open specification in 1987. During the same period other developers, who also were oblivious to the patent, incorporated the LZW algorithm into program code. Adobe postscript uses the algorithm. So do Tiff files, many archiving programs, and some modem file transfer programs.

Making a buck

It seems that Unisys finally discovered their patent in 1989 and started working out licensing terms. In 1994, after signing a licensing agreement for the GIF format, CompuServe attempted to pass the licensing costs on to its users. Confusion and anger reigned, and the LZW-free PNG format was the ultimate result of an attempt to avoid the licensing costs.

Things settled back down after CompuServe, Adobe, Corel, and other companies began licensing the algorithm. Then some companies apparently found a way to avoid paying royalty-based licensing fees. They charged for image editing software that did not support the GIF format, but included a free GIF plug-in with the software package.

Unisys keeps tightening its policies in an effort to eliminate these attempts at avoiding royalty payments on commercial software. But in doing so they seem to have made it difficult for some who want to license the technology. The tightening of the reins happened again earlier this year, when Unisys notified Web site operators that they are violating the patent if they post GIF graphics created with an unlicensed program.

Outraged, several open source advocates set up the Burn All GIFs Web site. On this site they called for replacing all GIF format files with PNG format files and designated 5 Nov. 1999 as "Burn all .gifs day." A 29 Aug. 1999 posting on slashdot.org, "Unisys Enforcing GIF Patents", provided fuel for the flames. Two days later another slashdot.org article, "Unisys Not Suing (most) Webmasters for Using GIFs", attempted to quell the flames. This article clarified the latest Unisys licensing policies and included comments from an interview with Mark Starr, General Patent and Technology Counsel for Unisys.

Wouldn't it be wonderful if GIF files could be replaced across the board with PNG files? Unfortunately, a complete replacement is not yet possible. For one thing, PNG has no support for animated graphics, so using it to replace animated GIFs is out. Some browsers, such as the Macintosh version of Microsoft Internet Explorer, have no support for PNG files. The current version of Netscape and the Windows version of Internet Explorer have various problems, including the inability to properly display PNG files with transparent backgrounds and interlaced images. There is a Web site that provides a complete list of PNG-enabled browsers along with their limitations.

The JPEG format is also not an adequate substitute for GIF. See either Squeeze the Most Out of Web Graphics or Stir-Fried Graphics for why it's not. And if you need a general purpose, loss-less compression algorithm, you might want to take a look at zlib.

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