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Portable Network Graphics (PNG)

format animated gif chunks

Definition: Portable Network Graphics (PNG) format uses lossless data compression andcontains support for device-independent color through gamma correction and the XYZ colormodel.  

The PNG (Portable Network Graphics) format was originally designed to replace the GIF format. PNG, now on version 1.2, is an International Standard (ISO/IEC 15948:2003), also released as a W3C Recommendation on November 10, 2003.

PNG uses lossless data compression and contains support for device-independent color through gamma correction and the XYZ color model. A PNG file consists of an 8-bytesignature (89 50 4E 47 0D 0A 1A 0A in hexadecimal) followed by a number of chunks, each of which conveys certain information about the image. Chunk types can come from threemain sources: the PNG standard, registered public chunk types maintained by the PNGDevelopment Group, and private chunks, defined by some applications. This chunk-basedstructure is designed to allow the PNG format to be extended while maintaining compatibilitywith older versions. Chunks follow the format shown in Table 1.

The MIME media type for PNG is image/png. Most current Web browsers support (most features of) the PNG format, paving the way for the PNG format to finally replace GIF forstill images.

An extension of PNG, called APNG (Animated Portable Network Graphics), has beenproposed to allow for animated PNG files, similar to their animated graphics interchangeformat (GIF) counterpart, but compatible with non-animated PNG files.

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