Portable Network Graphics Specification
Portable Network Graphics (PNG) Specification (Second Edition): Information technology- computer graphics and image processing - Portable Network Graphics (PNG); Functional specification ISO/IEC 15948:2003 (E)
This document describes PNG (Portable Network Graphics), 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-color, grayscale, and truecolor images are supported, plus an optional alpha channel. Sample depths range from 1 to 16 bits.