What does PNG mean?

PNG stands for Portable Network Graphics. It is an image format, it dates from 1995, and every part of the name was chosen deliberately: portable because it had to work identically on every machine, network because it was designed for images sent over one, graphics because it was aimed at logos and screenshots rather than photographs.

The people who wrote it also gave it a joke name. Early drafts called it PING, for “PING Is Not GIF” — a recursive acronym in the style of GNU. The joke tells you exactly what the format was for.

Why it was created at all

In 1987 CompuServe released GIF, and it became the way images moved around online. GIF used a compression method called LZW, and Unisys held a patent on LZW.

For seven years nobody made much of it. Then, at the end of 1994, Unisys announced it would enforce the patent and require licence fees from developers writing software that produced GIF files. Overnight, a format the whole internet depended on had an owner who wanted paying.

The response took about a week to start. A group on a Usenet mailing list began designing a replacement, and the first PNG specification was finished in early 1996. It was deliberately built on patent-free compression (DEFLATE, the same method inside ZIP files), it was published openly, and it was free to implement. In 2004 it became an ISO standard.

That origin explains most of PNG’s design. It was not trying to be a better photograph format. It was trying to be a GIF that nobody could charge for, and then it quietly became better than GIF at almost everything.

What lossless actually means

PNG is a lossless format. The word gets used loosely, so here is the precise version: the file you save contains enough information to reconstruct the original pixel grid exactly, value for value. Decode a PNG and you get back the numbers that went in.

Compare that with JPEG, which is lossy. JPEG achieves its small files by discarding information the eye is unlikely to miss — fine gradations of color, high-frequency detail in busy areas. The reconstruction is an approximation, and a good one, but it is not the original.

Three practical consequences follow.

Editing does not degrade the file. Open a PNG, crop it, save it, open it again, save it again. After fifty rounds it is still the same pixels. A JPEG re-compresses from the already-compressed version every time it is saved, and the damage accumulates. This is why work-in-progress files should not live as JPEGs.

Text and edges stay sharp. A screenshot saved as JPEG grows a faint halo of noise around every letter, because sharp black-on-white transitions are exactly the kind of high-frequency detail JPEG throws away. PNG has no such artifact, which is why every bug report with a legible screenshot in it is a PNG.

Photographs come out enormous. A 12-megapixel photo has no repeated regions for lossless compression to exploit, so PNG stores nearly all of it. The same photo is routinely five to ten times larger as a PNG than as a JPEG at quality most people cannot distinguish. Lossless is not a synonym for better. It is a trade, and for photographs it is usually the wrong side of the trade. The full comparison is in JPG vs PNG.

The other thing PNG brought: real transparency

GIF could mark one color as transparent. A pixel was either fully visible or fully gone, which is why old web graphics had jagged fringes around curved edges.

PNG added an alpha channel: a separate value per pixel describing how opaque it is, on a scale of 256 steps. A logo can fade smoothly into whatever background it lands on, and a drop shadow can be genuinely semi-transparent. Nothing else in common use offered this in 1995, and it is the single reason PNG became the default format for anything that has to sit on top of something else.

JPEG still cannot do transparency at all. If you need a transparent background, PNG or a newer format such as WebP is the only answer.

What PNG is not good at

Animation. The original specification has none. GIF kept that niche for two decades. An extension called APNG exists and browsers support it, but tool support is patchy and most people reach for video instead.

Photographs, as above. If your PNG is 8 MB and it is a picture of a beach, the format is the problem. Converting it to JPEG will cut the size by an order of magnitude with no visible change. You can do that in the browser with the image compressor, which lets you name the file size you need rather than guessing at a quality slider, and there is a broader guide to reducing file size covering the other file types.

Being small by default. PNG has real compression, but the ceiling is set by the content. Screenshots and flat graphics compress beautifully. Gradients, photographic noise, and anything scanned do not.

Pronouncing it

The specification says “ping”. Roughly nobody does. Both are understood, and the specification authors put the pronunciation in the standard precisely because they knew the argument was coming.