PNG (pronounced “ping”) is the Portable Network Graphics format, a format for storing bitmapped (raster) images on computers. Unofficially its acronym stands for “PNG’s Not GIF.” PNG was designed to be the successor to the once-popular GIF format, which became decidedly less popular right around New Year’s Day 1995 when Unisys and CompuServe suddenly announced that programs implementing GIF would require royalties, because of Unisys’ patent on the LZW compression method used in GIF. Since GIF had been showing its age in a number of ways even prior to that, the announcement only catalyzed the development of a new and much-improved replacement format. PNG is the result.
(By the way, despite the implications in some of CompuServe’s old press releases and in occasional trade-press articles, PNG’s development was not instigated by either CompuServe or the World Wide Web Consortium, nor was it led by them. Individuals from both organizations contributed to the effort, but the PNG development group exists as a separate, Internet-based entity.)
The motivation for creating the PNG format came in early 1995 when it came to light that the LZW data compression algorithm used in the GIF format had been patented by Unisys. There were also other problems with the GIF format which made a replacement desirable, notably its limitation to 256 colors at a time when computers capable of displaying far more than 256 colors were becoming common. Although GIF allows for animation, it was decided that PNG should be a single-image format. A companion format called MNG has been defined for animation.
* October 1, 1996 – Version 1.0 of the PNG specification was released, and later appeared as RFC 2083. It became a W3C Recommendation on 1996-10-01.
* December 31, 1998 – Version 1.1, with some small changes and the addition of three new chunks, was released.
* August 11, 1999 – Version 1.2, adding one extra chunk, was released.
* November 10, 2003 – PNG is now an International Standard (ISO/IEC 15948:2003). This version of PNG differs only slightly from version 1.2 and adds no new chunks.
* March 3, 2004 – ISO/IEC 15948:2004.
Note that the PNG specification was updated to version 1.1 on New Year’s Eve 1998 (that is, 31 December 1998). It included new chunks for cross-platform color correction (sRGB and iCCP), a revised and much more sensible description of gamma correction, and a number of other minor improvements and clarifications (all fully backward compatible, of course!). A second, more minor update (version 1.2) was released in August 1999; its only change was the addition of the iTXt chunk (international text).
In addition, PNG began the long process of international standardization* in 1999 (see the 10 May 1999 news item for details), thanks largely to its inclusion in VRML97. It finally completed that process and became the joint ISO/IEC standard 15948:2004 nearly five years later (see the 3 March 2004 news item), a few months after it was also rereleased by the W3C (with identical content) as their “PNG Second Edition” Recommendation.
*PNG was already part of the UK profile for MHEG-5 on digital terrestrial television; MHEG-5 is the international standard for a next-generation teletext system that shares a number of features with HTML. PNG is also used in MHP, the Java-based Multimedia Home Platform for digital video systems, and was included in HAVi, the somewhat defunct Home Audio-Video Interoperability standard for 1394-based home networking.
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