The patent required that all software supporting GIF pay royalties, leading to a flurry of criticism from Usenet users. The motivation for creating the PNG format was the realization that, on 28 December 1994, the Lempel–Ziv–Welch (LZW) data compression algorithm used in the Graphics Interchange Format (GIF) format was patented by Unisys. See also: Graphics Interchange Format § Unisys and LZW patent enforcement PNG was published as informational RFC 2083 in March 1997 and as an ISO/IEC 15948 standard in 2004. PNG files use the file extension PNG or png and are assigned MIME media type image/png. A PNG file contains a single image in an extensible structure of chunks, encoding the basic pixels and other information such as textual comments and integrity checks documented in RFC 2083. The PNG working group designed the format for transferring images on the Internet, not for professional-quality print graphics therefore non-RGB color spaces such as CMYK are not supported. PNG supports palette-based images (with palettes of 24-bit RGB or 32-bit RGBA colors), grayscale images (with or without an alpha channel for transparency), and full-color non-palette-based RGB or RGBA images. PNG was developed as an improved, non-patented replacement for Graphics Interchange Format (GIF) - unofficially, the initials PNG stood for the recursive acronym 'PNG's not GIF'.

Portable Network Graphics ( PNG, officially pronounced / p ɪ ŋ/ PING, sometimes pronounced / ˌ p iː ɛ n ˈ dʒ iː/ PEE-en- JEE) is a raster-graphics file format that supports lossless data compression.

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