W3C revises image format

The World Wide Web Consortium (W3C) on Monday recommended a second edition of the Portable Network Graphics (PNG, pronounced "ping") format, fixing 7 years' worth of errata and making minor technical adjustments.

And the format's second edition is getting a broader imprimatur. This time, it's also being published by the International Standardization Organization and the International Electrotechnical Commission, as ISO/IEC 15948:2003.

PNG was designed in response to a patent that had taken the Web by surprise. The patent, for the Lempel-Ziv-Welch, or LZW, a compression algorithm, forms the basis of the popular GIF (Graphics Interchange Format) design.

Once LZW patent owner Unisys announced its intention to seek royalties for the use of GIF graphics in software applications, free-software developers created PNG as a royalty free alternative.

While they were at it, they added some capabilities that GIF did not have, such as the ability to make images partially transparent.

Despite its added features and royalty free status, PNG has never approached GIF in terms of adoption. That's in part because of spotty support for the format by Microsoft's dominant Internet Explorer browser.

And this year PNG lost part of its original reason for being, when the LZW patent expired in the United States. The Canadian, Japanese, British, German, French and Italian LZW patents expire mid-2004.

An original author of the PNG format dismissed the notion that GIF's emergence into the public domain would harm PNG.

"That doesn't stop PNG from being technically superior to GIF," said Glenn Randers-Pehrson, editor of the PNG specification and a retired munitions engineer. "In addition to the partial transparencies, we have 16 million colors. That's opposed to 256 colors in GIF."

Randers-Pehrson also disputed the notion that PNG had not found users, and pointed out that by the measure of Google's image search engine, a substantial proportion of the Web's images use the format.

A Google search turned up roughly 3,050,000 JPEG images, 2,970,000 GIF images, and 994,000 PNG images.