How Patent Litigation Accelerated PNG Over GIF

In the mid-1990s, the Graphics Interchange Format (GIF) was the universally accepted standard for web graphics, but an aggressive patent enforcement campaign by Unisys Corporation disrupted the entire internet ecosystem. When Unisys announced plans to charge royalties on the compression algorithm used in GIF files, the threat of legal liability created an urgent need for an open, unencumbered alternative. This sudden legal pressure mobilized the software development community to design the Portable Network Graphics (PNG) format from the ground up, accelerating its development, standardization, and long-term adoption across the modern web.

The LZW Patent Trap

CompuServe originally developed the GIF specification in 1987 to enable efficient image transfers across dial-up networks. The format relied on the Lempel-Ziv-Welch (LZW) data compression algorithm, which effectively shrank file sizes without discarding image data. However, unbeknownst to CompuServe at the time, Sperry Corporation had already filed a patent for LZW in 1983.

In 1986, Sperry merged with the Burroughs Corporation to form Unisys, inheriting the patent rights to LZW. For years, Unisys made little effort to police the use of LZW in image files, allowing GIF to become the foundational image format of the early World Wide Web. Because developers assumed the format was essentially public domain, thousands of software utilities, graphics tools, and nascent web browsers were built around native GIF support.

The 1994 Ultimatum

In late December 1994, Unisys and CompuServe stunned the web community by announcing that developers of commercial software using GIF technology would have to pay licensing fees for the underlying LZW patent.

The announcement triggered immediate panic and widespread outrage across the web. Open-source developers, who could neither afford the licensing fees nor legally distribute proprietary code under permissive licenses, faced the threat of patent infringement lawsuits. The threat deepened in 1999 when Unisys clarified that non-commercial websites and individual webmasters using unlicensed software to create GIFs could also be held liable for a flat licensing fee of several thousand dollars. The realization that an essential building block of the internet was held hostage by intellectual property claims galvanized developers into action.

The Rapid Mobilization of PNG

Within days of the 1994 announcement, a collaborative group of software developers led by Thomas Boutell gathered on Usenet newsgroups—primarily comp.graphics—to create an open, royalty-free successor to GIF. Initially codenamed "PBF" (Portable Bitmap Format) and quickly renamed "PNG" (Portable Network Graphics), the project had one paramount objective: complete freedom from patent claims.

Rather than relying on LZW, the group engineered PNG around the patent-unencumbered DEFLATE compression algorithm, the same method utilized by Phil Katz’s PKZIP and the open-source zlib library. The creators took deliberate precautions to research and avoid known compression patents, ensuring that any developer could build PNG-compatible tools without fear of litigation.

Remarkably, the technical specification for PNG 1.0 was completed in early 1995, just months after the Unisys announcement. By 1996, the World Wide Web Consortium (W3C) officially recommended PNG as an internet standard.

Technical Superiority by Design

Although patent avoidance was the primary catalyst, the PNG working group designed the format to be fundamentally superior to GIF in nearly every functional metric:

The "Burn All GIFs" Campaign and Ultimate Adoption

The persistent threat of litigation sparked political and cultural resistance that accelerated PNG's deployment. In August 1999, the Free Software Foundation and the League for Programming Freedom launched the "Burn All GIFs" campaign. Activists gathered outside Unisys offices, encouraging webmasters to purge every static GIF from their web servers and replace them with PNG files.

While early web browser implementations—most notably Microsoft Internet Explorer 6—struggled with proper alpha-channel rendering, the looming threat of legal action forced major software vendors and the W3C to prioritize native PNG support. Open-source libraries like libpng made integration trivial for developers eager to insulate their applications from Unisys's claims.

The Long-Term Impact

The Unisys LZW patents finally expired worldwide between 2003 and 2004, freeing the GIF format from legal encumbrance. By that point, however, the damage was irreversible. The patent dispute had permanently discredited GIF as an archival and general-purpose lossless graphic format, preserving its utility only for short, looping animations.

The threat of litigation transformed PNG from an experimental project into an essential web pillar. In attempting to monetize an existing standard through patent enforcement, Unisys unintentionally catalyzed the creation of a technologically superior, completely open standard that ultimately superseded it.