LZW Patent Expiration Dates: US vs Europe

The Lempel-Ziv-Welch (LZW) data compression algorithm, which powered the ubiquitous Graphics Interchange Format (GIF), was at the center of one of the early internet's fiercest intellectual property battles. Held primarily by the Unisys Corporation, the patents covering LZW restricted software developers from freely creating GIF-compatible tools throughout the 1990s and early 2000s. Because patent terms and filing dates varied by jurisdiction, the LZW patent expired in the United States on June 20, 2003, whereas the corresponding European patents did not expire until June 18, 2004. This one-year gap created a period of legal uncertainty for international developers and digital content distributors.

The Origin of the LZW Patent Dispute

Terry Welch published the LZW compression technique in 1984 while working for the Sperry Corporation, which later merged with Burroughs to form Unisys. In 1987, CompuServe adopted LZW compression for its new GIF image standard, unaware that Unisys had applied for patent protection on the underlying algorithm.

In late 1994, Unisys announced it would begin enforcing its patent rights by requiring commercial software developers who used GIF compression to pay licensing fees. In 1999, Unisys expanded its enforcement efforts to include unlicensed software used by website owners and individual end users. This led to widespread backlash in the open-source and web development communities, prompting the creation of the patent-free Portable Network Graphics (PNG) format and advocacy movements like "Burn All GIFs."

United States Patent Expiration: June 20, 2003

The primary United States patent covering LZW was U.S. Patent 4,558,302, titled "High speed data compression and decompression apparatus and method."

Under historical U.S. patent law, utility patents lasted 17 years from the date of grant. However, following the Uruguay Round Agreements Act in 1995, U.S. patents filed before June 8, 1995, were granted an expiration term calculated as whichever was longer: 17 years from the grant date or 20 years from the filing date. Because 20 years from the June 20, 1983 filing date extended beyond 17 years from the grant date, the U.S. patent expired on June 20, 2003.

European Patent Expiration: June 18, 2004

Unisys sought international patent protection for LZW through the European Patent Office (EPO) under European Patent EP 0129794.

Under the European Patent Convention (EPC), patents have a standard term of 20 years from the filing date. Because the European application was filed roughly one year after the original U.S. filing, the resulting national patents in major European countries—including the United Kingdom, Germany, France, and Italy—remained valid until June 18, 2004. Additional related patents in Canada and Japan also expired around this period, with Canada's patent expiring on July 7, 2004, and Japan's expiring on June 20, 2004.

Implications of the One-Year Difference

The timing difference between the U.S. and European expirations produced a cross-border legal disparity:

  1. Global Software Distribution: Software released after June 2003 could legally compress GIFs in the United States without a Unisys license. However, distributing that same software in Europe, or hosting GIF-generation software on servers located in European jurisdictions, still technically infringed upon Unisys's active patents.
  2. Delayed Open-Source Adoption: Major open-source libraries and distributions that operated globally, such as Debian and Red Hat, remained cautious. Many maintainers waited until the European, Japanese, and Canadian patents lapsed before fully integrating native, unencumbered LZW compression tools into their default packages.

By July 2004, all key international patents on the LZW algorithm had expired, placing the GIF format permanently into the public domain worldwide.