The Portable Network Graphics format is gaining momentum as a free, Internet-based graphics standard.
With a number of technical advantages over the aging GIF format and the recent endorsement of the World Wide Web Consortium, Portable Network Graphics, or PNG (pronounced “ping”), is poised to become the Web graphics format of choice. Making good on that promise, though, requires the support of browser vendors Netscape Communications Corp. and Microsoft Corp.
The PNG format was conceived in early 1995, soon after Unisys Corp. announced that its patents on the LZW compression method covered the popular - and previously free - GIF format. Hoping to design a royalty-free alternative to GIF and overcome many of the old format’s limitations, a collection of Internet and graphics experts formed the PNG Group.
In recent months PNG has received a boost as a number of organizations and software developers announced their support. On Oct. 1 the World Wide Web Consortium gave its endorsement of the format.
The PNG specification offers a number of features geared toward graphics professionals, including built-in gamma and color correction, support for 48-bit color, and tight compression. PNG also sports a true alpha channel, allowing designers to blend images seamlessly in complex backgrounds.
PNG is also designed to support the addition of new features and retain compatibility with older image viewers. For example, one proposed extension to the format would embed multiple images in a single PNG file. A low-resolution image would be used for screen display, while a larger version would be used when printing to a high-resolution output device.
Another proposed extension would allow vector images and text call outs to be laid atop the image’s bit-mapped data. Viewers that did not support extensions to the standard PNG format would read the essential bit-map data and skip the extra information.
For PNG to attain widespread use it must be supported within Web browsers and applications - the former so that users can view the images without a plug-in, as is currently required, and the latter so that designers can save images in the PNG format.
A Microsoft spokesman said the company plans to support PNG in a future version of Internet Explorer for Windows 95, but the spokesman said Mac support has not been determined. A Netscape representative said only that the company is looking closely at the PNG format.
Adobe Photoshop 4.0, Macromedia FreeHand 7 Graphics Studio, and a number of popular freeware and shareware image-conversion utilities will also open and save PNG files. The Virtual Reality Modeling Language 2.0 standard, announced in August, also requires PNG support for compliance.
Still, some vendors are hesitant to adopt the standard. “We’re waiting for it to show up in the major browsers, honestly,” said Steve Guttman, vice president of marketing for Aptos, Calif.-based Fractal Design Corp. “We’d love to avoid paying a GIF licensing fee to Unisys; we’ll embrace PNG with open arms.”
In the meantime, designers can save images in PNG format either by using DeBabelizer from Equilibrium of Sausalito, Calif., or via a Photoshop plug-in from Infinop Inc. of Denton, Texas. Browser users can view those images with PNG Live, a free PNG display plug-in for Netscape Navigator developed by Infinop and New York-based Siegel & Gale.
Andrew Zolli, senior Internet technologist for Siegel & Gale, said PNG will be a dream come true for Web professionals. After the company’s Web designers became frustrated with GIF’s limitations, they began work on PNG Live.
“The designers were saying, ‘I wish we could get around the eight-bit limit,’” Zolli said, “and the production staff was saying, ‘I wish we could get around having to re-dither images every time we put them in a new context.’”
Though limitations in Netscape’s plug-in architecture prevent PNG Live from taking advantage of the format’s alpha channels, interest among users has been high. Zolli said the company had about 75,000 downloads of the plug-in in the first month.
Tom Lane, organizer of the Independent JPEG group and one of the PNG specification’s editors, agreed that support from Web-browser developers is critical. “It’s pretty clear that the main factor holding back PNG’s acceptance on the Web is that the largest browsers don’t handle it,” Lane said. "You can get plug-ins that provide partial support, but that’s not good enough to persuade Webmasters.
“I think that PNG will eventually come to be a dominant file format,” Lane said, “but I’m thinking in years, not weeks or months. It took that long for the existing standards to become widespread, and it will take that long for PNG.”