Chapter 16. PNG Format
The Portable Network Format (PNG for short—pronounced “ping”) is a versatile and full-featured graphics file format poised to make a big wave on the Web . . . it’s just taking its time doing so.
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) and 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 1-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 ...
Get Web Design in a Nutshell now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
