PNG Exists Because of a Christmas Eve Patent Demand
On December 24, 1994, Unisys announced it would charge royalties on every program that wrote a GIF. PNG was sketched within weeks.
GIF, designed by CompuServe in 1987, used a compression algorithm called LZW — Lempel-Ziv-Welch. CompuServe had not realized in 1987 that LZW was patented. Unisys held the patent and figured it out around 1993, and on December 24, 1994 the two companies jointly announced a licensing deal. Any software that read or wrote GIFs would now owe royalties: 1.5% of the program's price, or 15 cents per copy, whichever was greater.
The web, by 1994, was running on GIFs. Browsers, image editors, shareware paint programs — all of them wrote LZW. The reaction online was immediate and ugly. Developers had built freeware around an open format and discovered after the fact that the format wasn't open at all.
Thomas Boutell started organizing a replacement within weeks. The working group went through several names — including the in-joke "PING," for "PING Is Not GIF" — before settling on Portable Network Graphics. The first PNG specification shipped in 1996. It used a different, patent-free compression scheme (DEFLATE), added true color and an alpha channel, and was designed from the start to be unencumbered.
The Unisys patent expired in the United States on June 20, 2003 and in most other jurisdictions over the following year. By then PNG had taken over still images on the web, and the lesson had been absorbed everywhere: a format that survives is one nobody can charge for.
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