The PNG story Web Designing

PNG was developed in January and February 1995 as an effort to find a non-proprietary alternative to GIF when Unisys threatened to enforce its patent on LZW compression and collect licensing fees from developers of GIF-supporting programs. This caused a flurry of outrage and activity on the Internet.

Days after the announcement, Thomas Boutell posted the first draft of the PNG specification to the comp.graphics newsgroup. A community of programmers then quickly cooperated in specifying and implementing an impressive list of features:

  • 8-bit palette support (like GIF), support of 16-bit grayscale, and up to 48-bit truecolor (RGB) support
  • A lossless compression scheme and better compression than GIF for indexed color (palette) images
  • Two-dimensional progressive display that is more sophisticated than GIF's one dimensional interlacing
  • An alpha channel that can contain 8-bit or 16-bit transparency information, which means pixels can have up to 65,000 shades of transparency (not just "on" or "off" like GIF); 8-bit (256 shades of transparency) is far more common
  • Gamma correction information to make the PNG display with its intended brightness regardless of platform
  • Several methods for checking file integrity and corruption
  • Text storage capabilities for keyword information, such as copyright
  • Nonpatented compression free from licensing restrictions

The PNG format became an official W3C Recommendation in October of 1996. Since then, browser and software developers have given the format more attention, but there is still a long way to go.


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