You might have noticed that a lot of the graphics on my pages have .png as the file extension, and that the handful of .gif files are served up from other sites. That is because I have a serious problem with Unisys, holder of a patent on the LZW compression algorithm used in the GIF graphics file format, that prevents me from using the GIF format.

The problem starts back around 1986, when the GIF format was first put forward as a standard graphics file format for the CompuServe on-line service. One of the criteria CompuServe had for the format was that there be no licensing or similar restrictions on it. This made sense from CompuServe's point of view as a seller of content, since at the time there were a lot of types of computers out there with a lot of OSes and restrictions on the software to create and especially view the format would limit CompuServe's potential customer base. When GIF was put forward, the patent problem was noted and CompuServe almost dismissed the format from consideration because of it. This would have essentially killed GIF as a graphics file format, since CompuServe was then the single largest on-line service and if it wouldn't use the format then few others would support it. Only after assurances that there would be no licensing restrictions or other limitations on use of the compression algorithm was the format adopted.

Now, fast-forward a couple of years. GIF is now almost ubiquitous as a graphics file format. Unisys, out of the blue, goes back on it's original promise of no restrictions and proposes to charge royalties for use of it's algorithm. This caused a major outcry, including from Compuserve who, while not the giant they were, is still a 600-pound gorilla of an on-line service with a lot of customers. Some developers were so incensed at Unisys's turnabout that they formed a group and started development of a new format, Portable Network Graphics ( PNG ) that would not use patented algorithms. The outcry and the momentum to abandon GIF ( in much the same manner as the ARC compressed-archive format was abandoned in favor of PKZIP by the BBS world, for similar reasons ) was so great that Unisys backed down and promised that they would only charge royalties on commercial software to create GIF files, and that non-commercial software and software of any sort to only view GIFs would never be subject to royalties. Development of PNG continued, but most of the world settled back down to using GIFs.

Fast-forward again to 1999. Again out of the blue, Unisys announces it will begin charging royalties on it's patented algorithm, and would take action against those using the algorithm without paying the royalties. When asked, Unisys said outright that the royalty covered all software, commercial or non-commercial, that created, viewed or otherwise manipulated files using it's algorithm. Moreover, when asked by Webmasters, they said that Web sites that had GIF files on them, whether created by the site owner or not, would have to pay the royalty if they could not prove that all GIF files had never been touched by any software that had not licensed the LZW algorithm. This meant you were liable for the licensing fees even if you didn't create the file and never viewed it, as long as it was served up off your machine. And the fees weren't cheap. The cheapest license for individual, non-commercial use started at $5000, and Web sites would not fall under that category.

Note that this was the second time Unisys had reneged on their promise concerning the LZW algorithm and GIF files. In outrage, a lot of Webmasters took the step of, where possible, replacing the GIF images on their sites with PNG images which weren't subject to Unisys's patent. The general feeling was that if Unisys was going to go back on their word like this, then we simply didn't need to deal with them at all. That's where I stand. I will not do business with a company that makes a promise when it's to it's benefit to do so and then reneges on that promise when it's to it's benefit not to honor it's promise.

Moreover, PNG has some technical advantages over GIF:

1. GIF is limited to 256 colors in a given image. It cannot store 24-bit TrueColor images at all. PNG, on the other hand, can store anything from black-and-white bitmaps to 24-bit color cleanly and without losing information in the compression.
2. When dealing with transparent parts of the image, GIF is limited to either completely transparent or completely opaque. PNG, on the other hand, supports full alpha-channel transparency, providing 256 levels of translucency between completely transparent and completely opaque. This lets you create images which are translucent with the background partially visible through the image.

1. Many Web browsers don't completely support PNG yet. Netscape v4 and Internet Explorer v4 support non-transparent PNG images, and transparent images where parts of the image are either completely transparent or completely opaque. They do not yet support partial, or alpha-channel, transparency. The current Mozilla milestone builds support alpha-channel transparency correctly, so the final release of Netscape v6 and Mozilla should handle all PNG images correctly.
2. PNG doesn't support animated images. Given the amount of time I've wasted waiting for an animated advertising banner to download so I could actually see the page itself, I consider this a Good Thing. Philosophically, the PNG developers decided to concentrate on making PNG support images, not animation. They spun off a working group to develope a format called Multiframe Network Graphics ( MNG ), based on PNG, to handle animation. The idea was that, since animated images are almost always a base image plus a series of frames describing changes from the base image or previous frame, PNG could be used to describe the base image and the MNG group could concentrate on efficient ways of describing the frame-by-frame changes needed to animate the image, probably also using parts of PNG to store the graphics data for each frame.