Torvalds continues to direct the development of the kernel.39. History and development The motivation for creating the PNG format was in early 1995, after it had come to light that the Lempel–Ziv–Welch (LZW) data compression algorithm used in the GIF format had been patented by Unisys For more on this controversy, see: GIF (Unisys and LZW patent enforcement) There were also other problems with the GIF format which made a replacement desirable, notably its limitation to 256 colors at a time when computers capable of displaying far more than 256 colors were becoming common Although GIF allows for animation, it was decided that PNG should be a single-image format A companion format called MNG (Multi-image Network Graphics) has been defined for animation A January 1995 precursory discussion thread, on the usenet newsgroup "comp.graphics" with the subject Thoughts on a GIF-replacement file format, had many propositions, which would later be part of the PNG file format In this thread Oliver Fromme, author of the popular MS-DOS JPEG viewer QPEG, proposed the PING name, meaning PING is not GIF, and also the PNG extension for the first time. Portable Network Graphics PNG supports palette-based (palettes of 24-bit RGB or 32-bit RGBA colors), greyscale, greyscale with alpha, RGB, or RGBA images PNG was designed for transferring images on the Internet, not for print graphics, and so does not support non-RGB color spaces (such as CMYK) PNG files nearly always use file extension "PNG" or "png" and are assigned MIME media type "image/png" it was approved for this use by the Internet Engineering Steering Group on October 14, 1996. In fact, it’s been consistently ranked the best free photo editor for Mac, or close to it, since not long after its debut in 1996 ().Portable Network Graphics Portable Network Graphics PNG A PNG image with an 8-bit transparency channel (top) The same image is overlaid onto a checkered background (bottom), typically used in graphics software to indicate transparency Filename extension png Internet media type image/png Type code PNGf PNG Uniform Type Identifier public.png Developed by PNG Development Group (donated to W3C) Initial release OctoType of format lossless bitmap image format Extended to APNG, JNG and MNG Standard(s) ISO 15948, IETF RFC 2083 Open format? Yes Portable Network Graphics (PNG) is a bitmapped image format that employs lossless data compression PNG was created to improve upon and replace GIF (Graphics Interchange Format) as an image-file format not requiring a patent license It is pronounced /ˈpɪŋ/ ping, or pee-en-jee The PNG acronym is optionally recursive, unofficially standing for PNG's Not GIF. Why we love it: GIMP short for GNU Image Manipulation Program has long been a contender for the best free image editor. Where you can use it: Browsers for Mac, Windows, Linux.
![]() What Photo Editing Program Like Zondor Software To IndicatePLTE contains the palette list of colors IHDR must be the first chunk it contains the header. March 3, 2004: ISO/IEC 15948:2004 Technical details File header A PNG file starts with an 8-byte signature The hexadecimal byte values are 89 50 4E 47 0D 0A 1A 0A the decimal values are 137 80 78 71 13 10 26 10 Each of the header bytes is there for a specific reason: Bytes Purpose 89 Has the high bit set to detect transmission systems that not support bit data and to reduce the chance that a text file is mistakenly interpreted as a PNG, or vice versa 50 4E 47 In ASCII, the letters PNG, allowing a person to identify the format easily if it is viewed in a text editor 0D 0A A DOS-style line ending (CRLF) to detect DOS-UNIX line ending conversion of the data 1A A byte that stops display of the file under DOS when the command type has been used—the end-of-file character 0A A UNIX-style line ending (LF) to detect UNIX-DOS line ending conversion Portable Network Graphics "Chunks" within the file After the header comes a series of chunks, each of which conveys certain information about the image Chunks declare themselves as critical or ancillary, and a program encountering an ancillary chunk that it does not understand can safely ignore it This chunk-based storage layer structure, similar in concept to a container format, is designed to allow the PNG format to be extended while maintaining compatibility with older versions—it provides forward compatibility, and this same file structure (with different signature and chunks) is used in the associated MNG, JNG, and APNG formats A chunk consists of four parts: Length (4 bytes), Chunk type/name (4 bytes), Chunk data (length bytes) and CRC (Cyclic Redundancy Code / Checksum, bytes) Length (4 bytes) Chunk type (4 bytes) Chunk data CRC (length bytes) (4 bytes) Chunks are given a four letter case sensitive ASCII type/name compare FourCC The case of the different letters in the name (bit of the numeric value of the character) is a bit field that provides the decoder with some information on the nature of chunks it does not recognize The case of the first letter indicates if the chunk is critical or not If the first letter is uppercase, the chunk is critical if not, the chunk is ancillary Critical chunks contain information that is necessary to read the file If a decoder encounters a critical chunk it does not recognize, it must abort reading the file or supply the user with an appropriate warning The case of the second letter indicates if the chunk is "public" (either in the specification or the registry of special purpose public chunks) or "private" (not standardised) Uppercase is public and lowercase is private This ensures that public and private chunk names can never conflict with each other (although two private chunk names could conflict) The third letter must be uppercase to conform to the PNG specification It is reserved for future expansion Decoders should treat a chunk with a lower case third letter the same as any other unrecognised chunk The case of the fourth letter indicates if a chunk is safe to copy by editors that not recognize it If lowercase, the chunk may be safely copied regardless of the extent of modifications to the file If uppercase, it may only be copied if the modifications have not touched any critical chunks Critical chunks A decoder must be able to interpret these to read and render a PNG file November 10, 2003: PNG is now an International Standard (ISO/IEC 15948:2003) This version of PNG differs only slightly from version 1.2 and adds no new chunks August 11, 1999: Version 1.2, adding one extra chunk, was released December 31, 1998: Version 1.1, with some small changes and the addition of three new chunks, was released ![]()
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