The PNG Guide is an eBook based on Greg Roelofs' book, originally published by O'Reilly.

Mainstream Support and Present Status

If 1996 was the year of PNG's standardization, 1997 was the year of PNG applications. After having taken over libpng development from Guy Eric Schalnat in June 1996, Andreas Dilger shepherded it through versions 0.89 to 0.96, adding numerous features and finding and fixing bugs; application developers seemed not to mind the library's ``beta'' version number, and increasingly employed it in their mainstream apps. With native support in popular programs such as Adobe's Photoshop and Illustrator, Macromedia's Freehand, JASC's Paint Shop Pro, Ulead's PhotoImpact, and Microsoft's Office 97 suite, PNG's star was clearly rising. But perhaps the crowning moment came in the autumn, with fresh versions of the Big Two web browsers. Microsoft's Internet Explorer 4.0 in October and Netscape's Navigator 4.04 in November both included native, albeit somewhat limited, PNG support. At last, the widespread use of PNG on the Web came within the realm of possibility.

The theme for 1998 seems to have been maturity. Having been handed the reins of principal libpng development at the beginning of the year, Glenn Randers-Pehrson fixed many bugs, finished the documentation and generally polished libpng into a stable release worthy of a ``1.0'' version number by early March--three years to the day, in fact, after the PNG specification was frozen. In February, the UK Digital Television Group released the MHEG-5 UK Profile for next-generation teletext on digital terrestrial television; the profile included PNG as one of its bitmap formats, and as a result, manufacturers such as Philips, Sony, Pace and Nokia were expected to be shipping digital televisions and set-top boxes with built-in PNG support by the time this book reaches print. At the very end of March 1998, Netscape released Mozilla, the pre-alpha source code to Communicator 5.0, which allowed interested third parties (like the PNG Group) to tinker with the popular browser and make it work as intended. In October, the PNG Group approved some important additions and clarifications to one of the more difficult technical aspects of the PNG spec, namely, gamma and color correction; these changes defined the PNG 1.1 specification--the first official revision in three and a half years. And at roughly the same time, a joint committee of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) began the yearlong process to make Portable Network Graphics an official international standard (to be known as ISO/IEC 15948 upon approval).

But a history bereft of darker events is perhaps not so interesting...and, sadly enough, for a brief period in April 1998, it appeared that things might once again be percolating on the legal front. Specifically, there were rumors that Stac, Inc., believed the deflate compression engine in zlib (which is used by libpng) infringed on two of their patents. Careful reading of the patents in question, United States patents 4,701,745 and 5,016,009, suggests that although it is possible to write an infringing deflate engine, the one actually used in zlib does not do so.[55] Moreover, as this is written, a full year has passed with no public claims from Stac, no further private contacts, and no confirmation of the original rumors. However, until this is tested in court or Stac makes a public announcement clearing zlib of suspicion, at least a small cloud will remain over the Portable Network Graphics format as a whole. The irony should be evident to one and all.

[55] It should go without saying--but lawyers like it to be said anyway--that this is not official legal advice. Consult a patent attorney to be (more) certain. But note that deflate is also being standardized into open Internet protocols such as PPP.

Last Update: 2010-Nov-26