87-444: Paeth may refer to: Paeth filter , a filtering algorithm used in the compression of PNG images Alan W. Paeth (born 1956), Canadian computer scientist who developed the Paeth filter Sascha Paeth (born 1970), German musician Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with
174-588: A charter, a rationale, and a moderation policy if the group is to be moderated. Discussion of the new newsgroup proposal follows, and is finished with the members of the Big-8 Management Board making the decision, by vote, to either approve or disapprove the new newsgroup. Unmoderated newsgroups form the majority of Usenet newsgroups, and messages submitted by readers for unmoderated newsgroups are immediately propagated for everyone to see. Minimal editorial content filtering vs propagation speed form one crux of
261-603: A cross post to the *.answers group at the head of the hierarchy seen by some as a refining of information in that news group. Some subgroups are recursive—to the point of some silliness in alt.* . Usenet was originally created to distribute text content encoded in the 7- bit ASCII character set. With the help of programs that encode 8-bit values into ASCII, it became practical to distribute binary files as content. Binary posts, due to their size and often-dubious copyright status, were in time restricted to specific newsgroups, making it easier for administrators to allow or disallow
348-519: A depth of 8 bits per channel (24 bits per palette entry). Additionally, an optional list of 8-bit alpha values for the palette entries may be included; if not included, or if shorter than the palette, the remaining palette entries are assumed to be opaque. The palette must not have more entries than the image bit depth allows for, but it may have fewer (for example, if an image with 8-bit pixels only uses 90 colors then it does not need palette entries for all 256 colors). The palette must contain entries for all
435-454: A disproportionately high volume of customer support incidents (frequently complaining of missing news articles). Some ISPs outsource news operations to specialist sites, which will usually appear to a user as though the ISP itself runs the server. Many of these sites carry a restricted newsfeed, with a limited number of newsgroups. Commonly omitted from such a newsfeed are foreign-language newsgroups and
522-456: A flurry of criticism from Usenet users. One of them was Thomas Boutell, who on 4 January 1995 posted a precursory discussion thread on the Usenet newsgroup "comp.graphics" in which he devised a plan for a free alternative to GIF. Other users in that thread put forth many propositions that would later be part of the final file format. Oliver Fromme, author of the popular JPEG viewer QPEG , proposed
609-429: A mailing list associated with a CompuServe forum. The full specification of PNG was released under the approval of W3C on 1 October 1996, and later as RFC 2083 on 15 January 1997. The specification was revised on 31 December 1998 as version 1.1, which addressed technical problems for gamma and color correction . Version 1.2, released on 11 August 1999, added the iTXt chunk as the specification's only change, and
696-573: A moderator must bear the Approved: header line. Moderators ensure that the messages that readers see in the newsgroup conform to the charter of the newsgroup, though they are not required to follow any such rules or guidelines. Typically, moderators are appointed in the proposal for the newsgroup, and changes of moderators follow a succession plan. Historically, a mod.* hierarchy existed before Usenet reorganization. Now, moderated newsgroups may appear in any hierarchy, typically with .moderated added to
783-499: A news server might attempt to control the spread of spam by refusing to accept or forward any posts that trigger spam filters , or a server without high-capacity data storage may refuse to carry any newsgroups used primarily for file sharing , limiting itself to discussion-oriented groups. However, unlike BBSes and web forums, the dispersed nature of Usenet usually permits users who are interested in receiving some content to access it simply by choosing to connect to news servers that carry
870-682: A newsgroup under the Big Eight which contains discussions about children's books, but a group in the alt hierarchy may be dedicated to one specific author of children's books. Binaries are posted in alt.binaries.* , making it the largest of all the hierarchies. Many other hierarchies of newsgroups are distributed alongside these. Regional and language-specific hierarchies such as japan.* , malta.* and ne.* serve specific countries and regions such as Japan , Malta and New England . Companies and projects administer their own hierarchies to discuss their products and offer community technical support, such as
957-458: 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 or to Amiga ' s IFF , 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)
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#17328515802481044-412: A readership which is potentially widely distributed. These protocols most commonly use a flooding algorithm which propagates copies throughout a network of participating servers. Whenever a message reaches a server, that server forwards the message to all its network neighbors that haven't yet seen the article. Only one copy of a message is stored per server, and each server makes it available on demand to
1131-763: A reformatted version of 1.2 was released as a second edition of the W3C standard on 10 November 2003, and as an International Standard ( ISO/IEC 15948:2004 ) on 3 March 2004. Although GIF allows for animation , it was initially decided that PNG should be a single-image format. In 2001, the developers of PNG published the Multiple-image Network Graphics (MNG) format, with support for animation. MNG achieved moderate application support, but not enough among mainstream web browsers and no usage among web site designers or publishers. In 2008, certain Mozilla developers published
1218-689: A server, just (local) telephone service. The name Usenet comes from the term "users' network". The first Usenet group was NET.general , which quickly became net.general . The first commercial spam on Usenet was from immigration attorneys Canter and Siegel advertising green card services. On the Internet, Usenet is transported via the Network News Transfer Protocol (NNTP) on Transmission Control Protocol (TCP) port 119 for standard, unprotected connections, and on TCP port 563 for Secure Sockets Layer (SSL) encrypted connections. Usenet
1305-419: A significantly smaller file size. Before DEFLATE is applied, the data is transformed via a prediction method: a single filter method is used for the entire image, while for each image line, a filter type is chosen to transform the data to make it more efficiently compressible. The filter type used for a scanline is prepended to the scanline to enable inline decompression. There is only one filter method in
1392-432: A small subset of them. PNG offers a variety of transparency options. With true-color and grayscale images either a single pixel value can be declared as transparent or an alpha channel can be added (enabling any percentage of partial transparency to be used). For paletted images, alpha values can be added to palette entries. The number of such values stored may be less than the total number of palette entries, in which case
1479-457: A takedown petition to be most effective across the whole network, it would have to be issued to the origin server to which the content has been posted, before it has been propagated to other servers. Removal of the content at this early stage would prevent further propagation, but with modern high speed links, content can be propagated as fast as it arrives, allowing no time for content review and takedown issuance by copyright holders. Establishing
1566-513: A telecommunications service, and assert that they are not responsible for the user-posted binary content transferred via their equipment. In the United States, Usenet providers can qualify for protection under the DMCA Safe Harbor regulations , provided that they establish a mechanism to comply with and respond to takedown notices from copyright holders. Removal of copyrighted content from
1653-418: A tree-like form. When a user posts an article, it is initially only available on that user's news server. Each news server talks to one or more other servers (its "newsfeeds") and exchanges articles with them. In this fashion, the article is copied from server to server and should eventually reach every server in the network. The later peer-to-peer networks operate on a similar principle, but for Usenet it
1740-412: A two-stage compression process: PNG uses DEFLATE , a non-patented lossless data compression algorithm involving a combination of LZ77 and Huffman coding . Permissively licensed DEFLATE implementations, such as zlib , are widely available. Compared to formats with lossy compression such as JPEG, choosing a compression setting higher than average delays processing, but often does not result in
1827-521: Is a raster-graphics file format that supports lossless data compression . 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". 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. The PNG working group designed
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#17328515802481914-484: Is a separate table contained in the PLTE chunk. Sample data for a single pixel consists of a tuple of between one and four numbers. Whether the pixel data represents palette indices or explicit sample values, the numbers are referred to as channels and every number in the image is encoded with an identical format. The permitted formats encode each number as an unsigned integer value using a fixed number of bits, referred to in
2001-405: Is also used by individual users to store backup data. While commercial providers offer easier to use online backup services , storing data on Usenet is free of charge (although access to Usenet itself may not be). The method requires the uploader to cede control over the distribution of the data; the files are automatically disseminated to all Usenet providers exchanging data for the news group it
2088-518: Is based on an algorithm by Alan W. Paeth . Compare to the version of DPCM used in lossless JPEG , and to the discrete wavelet transform using 1 × 2, 2 × 1, or (for the Paeth predictor) 2 × 2 windows and Haar wavelets . Compression is further improved by choosing filter types adaptively on a line-by-line basis. This improvement, and a heuristic method of implementing it commonly used by PNG-writing software, were created by Lee Daniel Crocker , who tested
2175-403: Is contained within nine hierarchies, eight of which are operated under consensual guidelines that govern their administration and naming. The current Big Eight are: The alt.* hierarchy is not subject to the procedures controlling groups in the Big Eight, and it is as a result less organized. Groups in the alt.* hierarchy tend to be more specialized or specific—for example, there might be
2262-419: Is more sophisticated than GIF's 1-dimensional, 4-pass scheme, and allows a clearer low-resolution image to be visible earlier in the transfer, particularly if interpolation algorithms such as bicubic interpolation are used. However, the 7-pass scheme tends to reduce the data's compressibility more than simpler schemes. The core PNG format does not support animation. MNG is an extension to PNG that does; it
2349-589: 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 whether the chunk is "public" (either in the specification or the registry of special-purpose public chunks) or "private" (not standardized). 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
2436-500: Is normally the sender, rather than the receiver, who initiates transfers. Usenet was designed under conditions when networks were much slower and not always available. Many sites on the original Usenet network would connect only once or twice a day to batch-transfer messages in and out. This is largely because the POTS network was typically used for transfers, and phone charges were lower at night. The format and transmission of Usenet articles
2523-476: Is one such web based front end and some web browsers can access Google Groups via news: protocol links directly. A minority of newsgroups are moderated, meaning that messages submitted by readers are not distributed directly to Usenet, but instead are emailed to the moderators of the newsgroup for approval. The moderator is to receive submitted articles, review them, and inject approved articles so that they can be properly propagated worldwide. Articles approved by
2610-624: Is posted to. In general the user must manually select, prepare and upload the data. The data is typically encrypted because it is available to anyone to download the backup files. After the files are uploaded, having multiple copies spread to different geographical regions around the world on different news servers decreases the chances of data loss. Major Usenet service providers have a retention time of more than 12 years. This results in more than 60 petabytes (60000 terabytes ) of storage (see image). When using Usenet for data storage, providers that offer longer retention time are preferred to ensure
2697-491: Is similar to that of Internet e-mail messages. The difference between the two is that Usenet articles can be read by any user whose news server carries the group to which the message was posted, as opposed to email messages, which have one or more specific recipients. Today, Usenet has diminished in importance with respect to Internet forums , blogs , mailing lists and social media . Usenet differs from such media in several ways: Usenet requires no personal registration with
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2784-408: Is similar to the line above, since the differences from prediction will generally be clustered around 0, rather than spread over all possible image values. This is particularly important in relating separate rows, since DEFLATE has no understanding that an image is a 2D entity, and instead just sees the image data as a stream of bytes. There are five filter types for filter method 0; each type predicts
2871-400: Is sufficient storage allocated to handle the amount of articles being added. Without sufficient retention time, a reader will be unable to download all parts of the binary before it is flushed out of the group's storage allocation. This was at one time how posting undesired content was countered; the newsgroup would be flooded with random garbage data posts, of sufficient quantity to push out all
2958-443: Is used in the associated MNG , JNG , and APNG formats. A chunk consists of four parts: length (4 bytes, big-endian ), chunk type/name (4 bytes ), chunk data (length bytes) and CRC (cyclic redundancy code/checksum; 4 bytes ). The CRC is a network-byte-order CRC-32 computed over the chunk type and chunk data, but not the length. Chunk types are given a four-letter case sensitive ASCII type/name; compare FourCC . The case of
3045-502: The alt.binaries hierarchy which largely carries software, music, videos and images, and accounts for over 99 percent of article data. There are also Usenet providers that offer a full unrestricted service to users whose ISPs do not carry news, or that carry a restricted feed. Newsgroups are typically accessed with newsreaders : applications that allow users to read and reply to postings in newsgroups. These applications act as clients to one or more news servers. Historically, Usenet
3132-586: The Animated Portable Network Graphics (APNG) format with similar goals. APNG is a format that is natively supported by Gecko - and Presto -based web browsers and is also commonly used for thumbnails on Sony's PlayStation Portable system (using the normal PNG file extension). In 2017, Chromium based browsers adopted APNG support. In January 2020, Microsoft Edge became Chromium based, thus inheriting support for APNG. With this all major browsers now support APNG. The original PNG specification
3219-617: The Blink rendering engine; support was re-added in Opera 46 (inherited from Chromium 59). Microsoft Edge has supported APNG since version 79.0, when it switched to a Chromium-based engine. The PNG Group decided in April 2007 not to embrace APNG. Several alternatives were under discussion, including ANG, aNIM/mPNG, "PNG in GIF" and its subset "RGBA in GIF". However, currently only APNG has widespread support. With
3306-425: The sci.* hierarchy. Or, talk.origins and talk.atheism are in the talk.* hierarchy. When a user subscribes to a newsgroup, the news client software keeps track of which articles that user has read. In most newsgroups, the majority of the articles are responses to some other article. The set of articles that can be traced to one single non-reply article is called a thread . Most modern newsreaders display
3393-630: The "image/png" MIME media type. PNG was published as an informational RFC 2083 in March 1997 and as an ISO/IEC 15948 standard in 2004. The motivation for creating the PNG format was the realization, on 28 December 1994, that the Lempel–Ziv–Welch (LZW) data compression algorithm used in the Graphics Interchange Format (GIF) format was patented by Unisys . The patent required that all software supporting GIF pay royalties, leading to
3480-452: The (typically local) readers able to access that server. The collection of Usenet servers has thus a certain peer-to-peer character in that they share resources by exchanging them, the granularity of exchange however is on a different scale than a modern peer-to-peer system and this characteristic excludes the actual users of the system who connect to the news servers with a typical client-server application, much like an email reader. RFC 850
3567-653: The Mozilla Foundation. It is based on PNG, supports animation and is simpler than MNG. APNG offers fallback to single-image display for PNG decoders that do not support APNG. Today, the APNG format is supported by all major web browsers. APNG is supported in Firefox 3.0 and up, Pale Moon (all versions), and Safari 8.0 and up. Chromium 59.0 added APNG support, followed by Google Chrome. Opera supported APNG in versions 10–12.1, but support lapsed in version 15 when it switched to
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3654-537: The PING name, eventually becoming PNG, a recursive acronym meaning PING is not GIF , and also the .png extension . Other suggestions later implemented included the deflate compression algorithm and 24-bit color support, the lack of the latter in GIF also motivating the team to create their file format. The group would become known as the PNG Development Group, and as the discussion rapidly expanded, it later used
3741-421: The PNG specification as the bit depth . Notice that this is not the same as color depth , which is commonly used to refer to the total number of bits in each pixel, not each channel. The permitted bit depths are summarized in the table along with the total number of bits used for each pixel. The number of channels depends on whether the image is grayscale or color and whether it has an alpha channel . PNG allows
3828-414: 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 unrecognized chunk. The case of the fourth letter indicates whether the chunk is safe to copy by editors that do 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
3915-554: The Usenet community. One little cited defense of propagation is canceling a propagated message, but few Usenet users use this command and some news readers do not offer cancellation commands , in part because article storage expires in relatively short order anyway. Almost all unmoderated Usenet groups tend to receive large amounts of spam . Usenet is a set of protocols for generating, storing and retrieving news "articles" (which resemble Internet mail messages) and for exchanging them among
4002-400: The articles arranged into threads and subthreads. For example, in the wine-making newsgroup rec.crafts.winemaking, someone might start a thread called; "What's the best yeast?" and that thread or conversation might grow into dozens of replies long, by perhaps six or eight different authors. Over several days, that conversation about different wine yeasts might branch into several sub-threads in
4089-447: The content to be suppressed. This has been compensated by service providers allocating enough storage to retain everything posted each day, including spam floods, without deleting anything. Modern Usenet news servers have enough capacity to archive years of binary content even when flooded with new data at the maximum daily speed available. In part because of such long retention times, as well as growing Internet upload speeds, Usenet
4176-486: The current PNG specification (denoted method 0), and thus in practice the only choice is which filter type to apply to each line. For this method, the filter predicts the value of each pixel based on the values of previous neighboring pixels, and subtracts the predicted color of the pixel from the actual value, as in DPCM . An image line filtered in this way is often more compressible than the raw image line would be, especially if it
4263-559: The data will survive for longer periods of time compared to services with lower retention time. While binary newsgroups can be used to distribute completely legal user-created works, free software , and public domain material, some binary groups are used to illegally distribute proprietary software , copyrighted media, and pornographic material. ISP-operated Usenet servers frequently block access to all alt.binaries.* groups to both reduce network traffic and to avoid related legal issues. Commercial Usenet service providers claim to operate as
4350-635: The development of the Third Edition of the PNG Specification, now maintained by the PNG working group, APNG will finally be incorporated into the specification as an extension. 89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52 00 00 00 01 00 00 00 01 08 02 00 00 00 90 77 53 DE 00 00 00 0C 49 44 41 54 08 D7 63 F8 CF C0 00 00 03 01 01 00 18 DD 8D B0 00 00 00 00 49 45 4E 44 AE 42 60 82 .PNG.... ....IHDR ..............wS . ....IDAT..c.... ......... ....IEN D.B`. Displayed in
4437-402: The different letters in the name (bit 5 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 whether 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
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#17328515802484524-494: The entire Usenet network is a nearly impossible task, due to the rapid propagation between servers and the retention done by each server. Petitioning a Usenet provider for removal only removes it from that one server's retention cache, but not any others. It is possible for a special post cancellation message to be distributed to remove it from all servers, but many providers ignore cancel messages by standard policy, because they can be easily falsified and submitted by anyone. For
4611-526: The fashion of hex editors , with on the left side byte values shown in hex format , and on the right side their equivalent characters from ISO-8859-1 with unrecognized and control characters replaced with periods. Additionally the PNG signature and individual chunks are marked with colors. Note they are easy to identify because of their human readable type names (in this example PNG, IHDR, IDAT, and IEND). Reasons to use this International Standard: Usenet Early research and development: Merging
4698-524: The feeds they want. Usenet is culturally and historically significant in the networked world, having given rise to, or popularized, many widely recognized concepts and terms such as " FAQ ", " flame ", " sockpuppet ", and " spam ". In the early 1990s, shortly before access to the Internet became commonly affordable, Usenet connections via FidoNet 's dial-up BBS networks made long-distance or worldwide discussions and other communication widespread, not needing
4785-399: The files reaches a server. Binary newsgroups can be used to distribute files, and, as of 2022, some remain popular as an alternative to BitTorrent to share and download files. Each news server allocates a certain amount of storage space for content in each newsgroup. When this storage has been filled, each time a new post arrives, old posts are deleted to make room for the new content. If
4872-410: The following combinations of channels, called the color type . The color type is specified as an 8-bit value however only the low three bits are used and, even then, only the five combinations listed above are permitted. So long as the color type is valid it can be considered as a bit field as summarized in the adjacent table: With indexed color images, the palette always stores trichromatic colors at
4959-460: 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. 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. PNG files have the ".png" file extension and
5046-738: The group concerned; information need not be stored on a remote server; archives are always available; and reading the messages does not require a mail or web client, but a news client. However, it is now possible to read and participate in Usenet newsgroups to a large degree using ordinary web browsers since most newsgroups are now copied to several web sites. The groups in alt.binaries are still widely used for data transfer. Many Internet service providers, and many other Internet sites, operate news servers for their users to access. ISPs that do not operate their own servers directly will often offer their users an account from another provider that specifically operates newsfeeds. In early news implementations,
5133-476: The group name. Usenet newsgroups in the Big-8 hierarchy are created by proposals called a Request for Discussion, or RFD. The RFD is required to have the following information: newsgroup name, checkgroups file entry, and moderated or unmoderated status. If the group is to be moderated, then at least one moderator with a valid email address must be provided. Other information which is beneficial but not required includes:
5220-487: The highest end systems). Alpha storage can be "associated" (" premultiplied ") or "unassociated", but PNG standardized on "unassociated" ("non-premultiplied") alpha, which means that imagery is not alpha encoded ; the emissions represented in RGB are not the emissions at the pixel level. This means that the over operation will multiply the RGB emissions by the alpha, and cannot represent emission and occlusion properly. PNG uses
5307-670: The historical gnu.* hierarchy from the Free Software Foundation . Microsoft closed its newsserver in June 2010, providing support for its products over forums now. Some users prefer to use the term "Usenet" to refer only to the Big Eight hierarchies; others include alt.* as well. The more general term "netnews" incorporates the entire medium, including private organizational news systems. Informal sub-hierarchy conventions also exist. *.answers are typically moderated cross-post groups for FAQs. An FAQ would be posted within one group and
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#17328515802485394-425: The idea in 1979, and it was established in 1980. Users read and post messages (called articles or posts , and collectively termed news ) to one or more topic categories, known as newsgroups . Usenet resembles a bulletin board system (BBS) in many respects and is the precursor to the Internet forums that have become widely used. Discussions are threaded , as with web forums and BBSes, though posts are stored on
5481-616: The identity of the person posting illegal content is equally difficult due to the trust-based design of the network. Like SMTP email, servers generally assume the header and origin information in a post is true and accurate. However, as in SMTP email, Usenet post headers are easily falsified so as to obscure the true identity and location of the message source. In this manner, Usenet is significantly different from modern P2P services; most P2P users distributing content are typically immediately identifiable to all other users by their network address , but
5568-418: The inclusion of ICC color profiles . The lowercase first letter in these chunks indicates that they are not needed for the PNG specification. The lowercase last letter in some chunks indicates that they are safe to copy, even if the application concerned does not understand them. Pixels in PNG images are numbers that may be either indices of sample data in the palette or the sample data itself. The palette
5655-435: The local one, while the local server will receive any news its peers have that it currently lacks. This results in the automatic proliferation of content posted by any user on any server to any other user subscribed to the same newsgroups on other servers. As with BBSes and message boards, individual news servers or service providers are under no obligation to carry any specific content, and may refuse to do so for many reasons:
5742-649: The manual deletion of infringing material using the provisions of World Intellectual Property Organization treaty implementations, such as the United States Online Copyright Infringement Liability Limitation Act , but this would require giving notice to each individual news server administrator. On the Internet, Usenet is transported via the Network News Transfer Protocol (NNTP) on TCP Port 119 for standard, unprotected connections and on TCP port 563 for SSL encrypted connections. The major set of worldwide newsgroups
5829-513: The methods on many images during the creation of the format; the choice of filter is a component of file size optimization, as discussed below. If interlacing is used, each stage of the interlacing is filtered separately, meaning that the image can be progressively rendered as each stage is received; however, interlacing generally makes compression less effective. PNG offers an optional 2-dimensional, 7-pass interlacing scheme—the Adam7 algorithm . This
5916-763: The modifications have not touched any critical chunks. A decoder must be able to interpret critical chunks to read and render a PNG file. As stated in the World Wide Web Consortium , bit depth is defined as "the number of bits per sample or per palette index (not per pixel)". The PLTE chunk is essential for color type 3 (indexed color). It is optional for color types two and six (truecolor and truecolor with alpha) and it must not appear for color types 0 and 4 (grayscale and grayscale with alpha). Other image attributes that can be stored in PNG files include gamma values, background color, and textual metadata information. PNG also supports color management through
6003-419: The network bandwidth available to a server is high but the storage allocation is small, it is possible for a huge flood of incoming content to overflow the allocation and push out everything that was in the group before it. The average length of time that posts are able to stay on the server before being deleted is commonly called the retention time . Binary newsgroups are only able to function reliably if there
6090-534: The networks and creating the Internet: Commercialization, privatization, broader access leads to the modern Internet: Examples of Internet services: Usenet ( / ˈ j uː z n ɛ t / ), USENET , or, "in full", User's Network , is a worldwide distributed discussion system available on computers. It was developed from the general-purpose Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Ellis conceived
6177-456: The newly developed news software such as A News . The name "Usenet" emphasizes its creators' hope that the USENIX organization would take an active role in its operation. The articles that users post to Usenet are organized into topical categories known as newsgroups , which are themselves logically organized into hierarchies of subjects. For instance, sci.math and sci.physics are within
6264-412: The origin information for a Usenet posting can be completely obscured and unobtainable once it has propagated past the original server. Also unlike modern P2P services, the identity of the downloaders is hidden from view. On P2P services a downloader is identifiable to all others by their network address. On Usenet, the downloader connects directly to a server, and only the server knows the address of who
6351-434: The pixel values present in the image. The standard allows indexed color PNGs to have 1, 2, 4 or 8 bits per pixel; grayscale images with no alpha channel may have 1, 2, 4, 8 or 16 bits per pixel. Everything else uses a bit depth per channel of either 8 or 16. The combinations this allows are given in the table above. The standard requires that decoders can read all supported color formats, but many image editors can only produce
6438-421: The remaining entries are considered fully opaque. The scanning of pixel values for binary transparency is supposed to be performed before any color reduction to avoid pixels becoming unintentionally transparent. This is most likely to pose an issue for systems that can decode 16-bits-per-channel images (as is required for compliance with the specification) but only output at 8 bits per channel (the norm for all but
6525-484: The rise of the World Wide Web (WWW), web front-ends (web2news) have become more common. Web front ends have lowered the technical entry barrier requirements to that of one application and no Usenet NNTP server account. There are numerous websites now offering web based gateways to Usenet groups, although some people have begun filtering messages made by some of the web interfaces for one reason or another. Google Groups
6612-435: The server and newsreader were a single program suite, running on the same system. Today, one uses separate newsreader client software, a program that resembles an email client but accesses Usenet servers instead. Not all ISPs run news servers. A news server is one of the most difficult Internet services to administer because of the large amount of data involved, small customer base (compared to mainstream Internet service), and
6699-544: The server sequentially. A major difference between a BBS or web message board and Usenet is the absence of a central server and dedicated administrator or hosting provider. Usenet is distributed among a large, constantly changing set of news servers that store and forward messages to one another via "news feeds". Individual users may read messages from and post to a local (or simply preferred) news server, which can be operated by anyone, and those posts will automatically be forwarded to any other news servers peered with
6786-709: The title Paeth . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Paeth&oldid=962406592 " Categories : Disambiguation pages Disambiguation pages with surname-holder lists Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Portable Network Graphics#Filtering [REDACTED] Portable Network Graphics ( PNG , officially pronounced / p ɪ ŋ / PING , colloquially pronounced / ˌ p iː ɛ n ˈ dʒ iː / PEE -en- JEE )
6873-507: The traffic. The oldest widely used encoding method for binary content is uuencode , from the Unix UUCP package. In the late 1980s, Usenet articles were often limited to 60,000 characters, and larger hard limits exist today. Files are therefore commonly split into sections that require reassembly by the reader. With the header extensions and the Base64 and Quoted-Printable MIME encodings, there
6960-485: The value of each byte (of the image data before filtering) based on the corresponding byte of the pixel to the left ( A ), the pixel above ( B ), and the pixel above and to the left ( C ) or some combination thereof, and encodes the difference between the predicted value and the actual value. Filters are applied to byte values, not pixels; pixel values may be one or two bytes, or several values per byte, but never cross byte boundaries. The filter types are: The Paeth filter
7047-515: Was a new generation of binary transport. In practice, MIME has seen increased adoption in text messages, but it is avoided for most binary attachments. Some operating systems with metadata attached to files use specialized encoding formats. For Mac OS, both BinHex and special MIME types are used. Other lesser known encoding systems that may have been used at one time were BTOA , XX encoding , BOO , and USR encoding. In an attempt to reduce file transfer times, an informal file encoding known as yEnc
7134-462: Was associated with the Unix operating system developed at AT&T , but newsreaders were soon available for all major operating systems. Email client programs and Internet suites of the late 1990s and 2000s often included an integrated newsreader. Newsgroup enthusiasts often criticized these as inferior to standalone newsreaders that made correct use of Usenet protocols, standards and conventions. With
7221-457: Was authored by an ad hoc group of computer graphics experts and enthusiasts. Discussions and decisions about the format were conducted by email. The original authors listed on RFC 2083 are: A PNG file starts with an eight- byte signature (refer to hex editor image on the right): 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
7308-625: Was conceived in 1979 and publicly established in 1980, at the University of North Carolina at Chapel Hill and Duke University , over a decade before the World Wide Web went online (and thus before the general public received access to the Internet ), making it one of the oldest computer network communications systems still in widespread use. It was originally built on the "poor man's ARPANET ", employing UUCP as its transport protocol to offer mail and file transfers, as well as announcements through
7395-459: Was designed by members of the PNG Group. MNG shares PNG's basic structure and chunks, but it is significantly more complex and has a different file signature, which automatically renders it incompatible with standard PNG decoders. This means that most web browsers and applications either never supported MNG or dropped support for it. The complexity of MNG led to the proposal of APNG by developers at
7482-429: Was introduced in 2001. It achieves about a 30% reduction in data transferred by assuming that most 8-bit characters can safely be transferred across the network without first encoding into the 7-bit ASCII space. The most common method of uploading large binary posts to Usenet is to convert the files into RAR archives and create Parchive files for them. Parity files are used to recreate missing data when not every part of
7569-450: Was the first formal specification of the messages exchanged by Usenet servers. It was superseded by RFC 1036 and subsequently by RFC 5536 and RFC 5537. In cases where unsuitable content has been posted, Usenet has support for automated removal of a posting from the whole network by creating a cancel message, although due to a lack of authentication and resultant abuse, this capability is frequently disabled. Copyright holders may still request
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