V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

PNG
       Portable Network Graphics [format] (RFC 2083)


The Free On-line Dictionary of Computing (30 December 2018):

Portable Network Graphics
PNG

    /ping/ (PNG) An extensible file format for the
   lossless, portable, well-compressed storage of raster
   images.  PNG provides a patent-free replacement for GIF and
   can also replace many common uses of TIFF.
   Indexed-colour, greyscale and truecolour images are
   supported, plus an optional alpha channel.  Sample depths
   range from 1 to 16 bits.

   PNG is designed for on-line viewing applications, such as the
   World Wide Web, so it is fully streamable with a
   progressive display option.  PNG is robust, providing both
   full file integrity checking and simple detection of common
   transmission errors.  Also, PNG can store gamma correction
   and chromaticity data for improved colour matching on
   heterogeneous platforms.

   Filename extension: .png.

   RFC 2083.  W3C PNG pages
   (http://w3.org/Graphics/PNG/).  PNG home page
   (http://wco.com/~png/).

   (1997-08-07)