The trigger: December 28, 1994
The story of PNG doesn't begin with an idea — it begins with a press release. On December 28, 1994, Unisys announced that it would start charging license fees for using the LZW compression algorithm — the very algorithm at the heart of GIF, the dominant image format of the day. CompuServe, which had originally created GIF (more on that in our GIF history article), passed the notice along to software vendors: anyone shipping a GIF encoder would now have to pay Unisys a royalty.
The young, commercial web went into shock. Within a few weeks, a loose group of open-source developers came together determined to build a patent-free replacement. Their spokesperson was Thomas Boutell, author of the popular GD library; alongside him was Adam M. Costello(Berkeley), who suggested the name "PNG." The official quip behind it: "PNG's Not GIF" — a recursive acronym that symbolized the exact opposite of the patent fight.
1995–1996: a format in 12 months
What started as a mailing list (png-list@uunet.uu.net, founded in January 1995) became a finished specification within a year. The developers never met in person, coordinated everything by email, and produced the first final version on October 1, 1996. As early as March 1997, PNG was published as RFC 2083 by the IETF — an unusually fast standardization, driven by the urgency of the patent question.
Three design goals were front and center: lossless, patent-free, web-friendly. Lossless meant "no pixel is altered" — unlike the then-new JPEG. Patent-free meant "Deflate instead of LZW" — the developers adopted the compression algorithm from the already-free zlib/gzip ecosystem, itself descended from Phil Katz's PKZIP legacy. Web-friendly meant "streamable" — PNG images can be displayed progressively, byte by byte, which was a must-have with the 28-Kbps modems of the era.
The killer feature: the alpha channel
In hindsight, PNG's real breakthrough wasn't patent-free compression but the alpha channel. GIF could only do binary transparency — a pixel was either fully visible or fully transparent. PNG introduced 8-bit alpha per pixel: 255 gradations between fully opaque and fully transparent. That made soft edges, drop shadows, and believable compositing over any background possible.
This step shaped two decades of digital design. UI icons with genuine anti-aliased edges, app symbols that look equally good on light and dark themes, logos on the web without an ugly edge halo — none of that was possible before PNG. The significance of this design layer shows up in modern PWA practice too; see our PWA app icons history article.
libpng: the library behind the format
Alongside the specification came libpng, the reference C library that is still baked into practically every browser, operating system, and image-editing program today. Written by Guy Eric Schalnat (Group 42) and maintained since 1995 by Glenn Randers-Pehrson, libpng is one of the longest-lived single-purpose open-source projects. A full re-implementation in another language (e.g. rust-png) is the exception; most of the time libpng is pulled in via FFI.
The practical consequence: whenever a security hole is found in libpng (which has happened roughly a dozen times since 1996), browser vendors worldwide ship patches within a few days. PNG decoders are a piece of critical infrastructure that almost no one consciously notices.
2008: PNG becomes ISO/IEC 15948
Ten years after the initial specification, PNG was also anchored in international standardization as ISO/IEC 15948 — a formality that mattered to regulated industries (medical imaging, government documentation). The spec barely changed in the process; it was simply cast into a formal ISO framework.
APNG: the unloved animation
One of the stranger episodes in PNG's history is APNG (Animated PNG). Mozilla staff proposed a backward-compatible animation extension in 2004 — much like animated GIF, but with real colors and alpha. The PNG committee officially rejected the proposal; Mozilla implemented it in Firefox anyway and published its own specification in 2008. It took until 2017 for Chrome and Safari to follow suit. Today APNG is broadly supported, but has largely been superseded by animated WebP; see GIF vs. WebP for animations.
Optimization tools: pngcrush, optipng, oxipng, ECT
Because PNG is lossless, its optimization revolves around clever encoding rather than "less quality." Three levers: choosing the per-row filter strategy (None, Sub, Up, Average, Paeth), reducing to indexed palettes (PNG-8), and stripping unnecessary chunks (embedded EXIF, ICC profiles, Photoshop edit history). Tools like pngcrush (Glenn Randers-Pehrson, 1998), optipng (Cosmin Truța), oxipng(a Rust re-implementation), and today's frontrunner ECT (Efficient Compression Tool) achieve 30–60% size reduction versus standard exports — without a single pixel looking any different.
Our PNG compressorruns a similar pipeline entirely in the browser — no file ever leaves your machine. If you want the background on encoder choice, you'll find it in the big compression guide.
2023–2026: PNG-3 and the HDR extension
For a long time PNG was considered a "finished specification." In 2023, however, a W3C working group started on PNG-3, which primarily brought two extensions: native HDR support (previously you had to resort to tone-mapping tricks) and an officially standardized APNG variant. In June 2025, PNG (Third Edition) was ratified as a W3C Recommendation — the first major PNG update in decades, and already implemented in most browsers.
Why PNG is here to stay
Even in 2026, PNG plays a role that lossless WebP and lossless AVIF can't take over: structural simplicity. The specification is barely 100 pages long, the reference decoder is under 10,000 lines of C, and every embedded system from 32-bit up can decode it without hardware acceleration. That makes PNG the safe choice for screenshots, diagrams, UI icons, and anything that should still be openable 20 years from now — see also our SVG/PNG/JPG for iconscomparison. For classic photos, JPEG remains the more efficient choice, and for modern web delivery it's WebP or AVIF; but for the lossless niche — painted graphics, pixel art, logos with an alpha channel, technical screenshots — PNG is structurally unchallenged.
Sources
RFC 2083 — PNG (Portable Network Graphics) Specification · W3C Recommendation PNG (Third Edition) · ISO/IEC 15948 — PNG · libpng project site · Mozilla APNG specification · Unisys LZW FAQ (Web Archive, 1996) · Greg Roelofs, "PNG: The Definitive Guide," O'Reilly 1999.