PNG Second Edition has now become a W3C Recommendation. The World Wide Web Consortium (W3C) have released the Portable Network Graphics (PNG) Specification (2nd Edition) as a W3C Recommendation and also an International Standard, ISO/IEC 15948:2003.
PNG is a graphics file format that is used for raster images, including the use of Indexed-color, grayscale, truecolor, and additional support to the alpha channel. More information can be found in the W3C Graphics Activity website.