HOME

TheInfoList




JPEG ( ) is a commonly used method of
lossy compression In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...
for
digital image A digital image is an composed of s, also known as ''pixels'', each with ', ' of numeric representation for its or that is an output from its fed as input by its denoted with ''x'', ''y'' on the x-axis and y-axis, respectively. Depending on ...
s, particularly for those images produced by
digital photography Digital photography uses cameras A camera is an optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the ...
. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and
image qualityImage quality can refer to the level of accuracy in which different imaging systems capture, process, store, compress, transmit and display the signals that form an image. Another definition refers to image quality as "the weighted combination of all ...
. JPEG typically achieves 10:1 compression with little perceptible loss in image quality. Since its introduction in 1992, JPEG has been the most widely used
image compression Image compression is a type of data compression In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image proc ...
standard in the world, and the most widely used digital
image format Image file formats are standardized means of organizing and storing digital image A digital image is an image File:TEIDE.JPG, An Synthetic aperture radar, SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on board the Spac ...
, with several billion JPEG images produced every day as of 2015. The term "JPEG" is an initialism/acronym for the
Joint Photographic Experts Group The Joint Photographic Experts Group (JPEG) is the joint committee between / / and that created and maintains the , , , , , , and related standards. It also has the responsibility for maintenance of the and standards that were developed by the ...
, which created the standard in 1992. The basis for JPEG is the
discrete cosine transform A discrete cosine transform (DCT) expresses a finite sequence of data points In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics ...
(DCT), a lossy image compression technique that was first proposed by Nasir Ahmed in 1972. JPEG was largely responsible for the proliferation of digital images and
digital photo Digital photography uses cameras A camera is an optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the ...
s across the Internet, and later
social media Social media are interactive technologies that facilitate the creation Creation may refer to: Religion * Creation ''ex nihilo'', the concept that matter was created by God out of nothing * Creation myth A creation myth (or cosmogonic myth) ...

social media
. JPEG compression is used in a number of
image file formats Image file formats are standardized means of organizing and storing digital image A digital image is an image File:TEIDE.JPG, An Synthetic aperture radar, SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on board the Spac ...
. JPEG/
Exif Exchangeable image file format (officially Exif, according to JEIDA/JEITA/CIPA specifications) is a standard that specifies the formats for image File:TEIDE.JPG, An Synthetic aperture radar, SAR radar imaging, radar image acquired by the S ...
is the most common image format used by
digital camera A digital camera is a camera A camera is an optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behav ...

digital camera
s and other photographic image capture devices; along with JPEG/
JFIF The JPEG File Interchange Format (JFIF) is an standard published as Recommendation T.871 and 10918-5. It defines supplementary specifications for the that contains the image data encoded with the algorithm. The base specifications for a JPEG c ...
, it is the most common format for storing and transmitting
photographic image File:View_from_the_Window_at_Le_Gras_colorized_2020_new.png, 396x396px, ''View from the Window at Le Gras'' (1826 or 1827), by Nicéphore Niépce, the earliest known surviving photograph of a real-world scene, made with a camera obscura. Origina ...
s on the
World Wide Web The World Wide Web (WWW), commonly known as the Web, is an information system An information system (IS) is a formal, sociotechnical Sociotechnical systems (STS) in organizational development is an approach to complex organizational ...
. These format variations are often not distinguished, and are simply called JPEG. The
MIME media type Multipurpose Internet Mail Extensions (MIME) is an Internet standard that extends the format of email upThe email_address.html"_;"title="at_sign,_a_part_of_every_SMTP_email_address">at_sign,_a_part_of_every_SMTP_email_address Electronic ...
for JPEG is ''image/jpeg'', except in older
Internet Explorer Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, (from August 16, 1995 to March 30, 2021) commonly abbreviated IE or MSIE) is a discontinued series of s developed by and included in the line of s, starti ...
versions, which provides a MIME type of ''image/pjpeg'' when uploading JPEG images. JPEG files usually have a
filename extension A filename extension, file extension or file type is an identifier specified as a suffix to the name A name is a term used for identification by an external observer. They can identify a class or category of things, or a single thing, either un ...
of .jpg or .jpeg. JPEG/JFIF supports a maximum image size of 65,535×65,535 pixels, hence up to 4 gigapixels for an
aspect ratio The aspect ratio of a geometric Geometry (from the grc, γεωμετρία; '' geo-'' "earth", '' -metron'' "measurement") is, with arithmetic Arithmetic (from the Ancient Greek, Greek wikt:en:ἀριθμός#Ancient Greek, ἀριθμό ...
of 1:1. In 2000, the JPEG group introduced a format intended to be a successor,
JPEG 2000 JPEG 2000 (JP2) is an image compression Image compression is a type of data compression In signal processing, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original r ...
, but it was unable to replace the original JPEG as the dominant image standard.


History


Background

The original JPEG specification published in 1992 implements processes from various earlier
research papers Academic publishing is the subfield of publishing Publishing is the activity of making information, literature, music, software and other content available to the public for sale or for free. Traditionally, the term refers to the distributio ...
and
patents A patent is a type of intellectual property Intellectual property (IP) is a category of property that includes intangible creations of the human intellect. There are many types of intellectual property, and some countries recognize more than ...
cited by the
CCITT The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications Telecommunication is the transmission of information by various types of technologies over , radio, , or other systems. It has its origin ...
(now
ITU-T The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications and Information Communication Technology such as X.509 for cybersecurity, Y.3172 and Y.3173 for machine learning, and H.264/MPEG-4 AVC for video ...
) and Joint Photographic Experts Group. The main basis for JPEG's
lossy compression In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...
algorithm is the
discrete cosine transform A discrete cosine transform (DCT) expresses a finite sequence of data points In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics ...
(DCT), which was first proposed by Nasir Ahmed as an
image compression Image compression is a type of data compression In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image proc ...
technique in 1972. Ahmed developed a practical DCT algorithm with T. Natarajan of
Kansas State University Kansas State University (KSU, Kansas State, or K-State) is a public In public relations and communication science, publics are groups of individual people, and the public (a.k.a. the general public) is the totality of such groupings. Thi ...
and
K. R. Rao Kamisetty Ramamohan Rao was an Indian-American electrical engineer. He was a professor of Electrical Engineering at the University of Texas at Arlington (UT Arlington). Academically known as K. R. Rao, he is credited with the co-invention of ...
of the
University of Texas The University of Texas at Austin, shortened to UT Austin, UT, or Texas, is a public In public relations and communication science, publics are groups of individual people, and the public (a.k.a. the general public) is the totality of s ...
in 1973. Their seminal 1974 paper is cited in the JPEG specification, along with several later research papers that did further work on DCT, including a 1977 paper by Wen-Hsiung Chen, C.H. Smith and S.C. Fralick that described a fast DCT algorithm, as well as a 1978 paper by N.J. Narasinha and S.C. Fralick, and a 1984 paper by B.G. Lee. The specification also cites a 1984 paper by Wen-Hsiung Chen and W.K. Pratt as an influence on its quantization algorithm, and
David A. Huffman David Albert Huffman (August 9, 1925 – October 7, 1999) was an American pioneer in computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as pr ...
's 1952 paper for its
Huffman coding In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algor ...
algorithm. The JPEG specification cites patents from several companies. The following patents provided the basis for its
arithmetic coding Arithmetic coding is a form of entropy encoding In information theory, an entropy coding (or entropy encoding) is a lossless compression , lossless data compression scheme that is independent of the specific characteristics of the medium. One of ...
algorithm. *
IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the C ...

IBM
** February 4, 1986 Kottappuram M. A. Mohiuddin and Jorma J. Rissanen Multiplication-free multi-alphabet arithmetic code ** February 27, 1990 G. Langdon, J.L. Mitchell, W.B. Pennebaker, and Jorma J. Rissanen Arithmetic coding encoder and decoder system ** June 19, 1990 W.B. Pennebaker and J.L. Mitchell Probability adaptation for arithmetic coders *
Mitsubishi Electric , established on 15 January 1921, is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Mult ...
**
1021672
January 21, 1989 Toshihiro Kimura, Shigenori Kino, Fumitaka Ono, Masayuki Yoshida Coding system **
2-46275
February 26, 1990 Fumitaka Ono, Tomohiro Kimura, Masayuki Yoshida, and Shigenori Kino Coding apparatus and coding method The JPEG specification also cites three other patents from IBM. Other companies cited as patent holders include
AT&T AT&T Inc. is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, a s ...

AT&T
(two patents) and Canon Inc. Absent from the list is , filed by Compression Labs' Wen-Hsiung Chen and Daniel J. Klenke in October 1986. The patent describes a DCT-based image compression algorithm, and would later be a cause of controversy in 2002 (see '' Patent controversy'' below). However, the JPEG specification did cite two earlier research papers by Wen-Hsiung Chen, published in 1977 and 1984.


JPEG standard

"JPEG" stands for
Joint Photographic Experts Group The Joint Photographic Experts Group (JPEG) is the joint committee between / / and that created and maintains the , , , , , , and related standards. It also has the responsibility for maintenance of the and standards that were developed by the ...
, the name of the committee that created the JPEG standard and also other still picture coding standards. The "Joint" stood for
ISO The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task w ...

ISO
TC97 WG8 and
CCITT The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications Telecommunication is the transmission of information by various types of technologies over , radio, , or other systems. It has its origin ...
SGVIII. Founded in 1986, the group developed the JPEG standard during the late 1980s. Among several
transform coding Transform coding is a type of data compression In signal processing, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is e ...
techniques they examined, they selected the
discrete cosine transform A discrete cosine transform (DCT) expresses a finite sequence of data points In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics ...
(DCT), as it was by far the most efficient practical compression technique. The group published the JPEG standard in 1992. In 1987, ISO TC 97 became ISO/IEC JTC1 and, in 1992, CCITT became ITU-T. Currently on the JTC1 side, JPEG is one of two sub-groups of
ISO The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task w ...
/
IECIEC may refer to: Businesses and organisations * International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organizati ...
Joint Technical Committee 1, Subcommittee 29, Working Group 1 (
ISO/IEC JTC 1/SC 29ISO/IEC JTC 1/SC 29 Coding of audio, picture, multimedia and hypermedia information is a standardization subcommittee of the Joint Technical Committee ISO/IEC JTC1, ISO/IEC JTC 1 of the International Organization for Standardization (ISO) and the Int ...
/WG 1) – titled as ''Coding of still pictures''. On the ITU-T side, ITU-T SG16 is the respective body. The original JPEG Group was organized in 1986, issuing the first JPEG standard in 1992, which was approved in September 1992 as
ITU-T The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications and Information Communication Technology such as X.509 for cybersecurity, Y.3172 and Y.3173 for machine learning, and H.264/MPEG-4 AVC for video ...
Recommendation T.81 and, in 1994, as
ISO The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task w ...
/
IECIEC may refer to: Businesses and organisations * International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organizati ...
10918-1. The JPEG standard specifies the
codec A codec is a device or computer program In imperative programming, a computer program is a sequence of instructions in a programming language that a computer can execute or interpret. In declarative programming, a ''computer program'' is a Set ...
, which defines how an image is compressed into a stream of
byte The byte is a unit of digital information that most commonly consists of eight bit The bit is a basic unit of information in computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It ...
s and decompressed back into an image, but not the file format used to contain that stream. The
Exif Exchangeable image file format (officially Exif, according to JEIDA/JEITA/CIPA specifications) is a standard that specifies the formats for image File:TEIDE.JPG, An Synthetic aperture radar, SAR radar imaging, radar image acquired by the S ...
and
JFIF The JPEG File Interchange Format (JFIF) is an standard published as Recommendation T.871 and 10918-5. It defines supplementary specifications for the that contains the image data encoded with the algorithm. The base specifications for a JPEG c ...
standards define the commonly used file formats for interchange of JPEG-compressed images. JPEG standards are formally named as ''Information technology – Digital compression and coding of continuous-tone still images''. ISO/IEC 10918 consists of the following parts:
Ecma International Ecma International () is a Nonprofit organization, nonprofit standards organization for information and communication systems. It acquired its current name in 1994, when the European Computer Manufacturers Association (ECMA) changed its name to ...
TR/98 specifies the JPEG File Interchange Format (JFIF); the first edition was published in June 2009.


Patent controversy

In 2002, Forgent Networks asserted that it owned and would enforce
patent A patent is a type of intellectual property Intellectual property (IP) is a category of property Property is a system of rights that gives people legal control of valuable things, and also refers to the valuable things themselves. Depe ...

patent
rights on the JPEG technology, arising from a patent that had been filed on October 27, 1986, and granted on October 6, 1987: by Compression Labs' Wen-Hsiung Chen and Daniel J. Klenke. While Forgent did not own Compression Labs at the time, Chen later sold Compression Labs to Forgent, before Chen went on to work for
Cisco Cisco Systems, Inc. (Cisco) is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multin ...

Cisco
. This led to Forgent acquiring ownership over the patent. Forgent's 2002 announcement created a furor reminiscent of
Unisys Unisys Corporation is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational sta ...
' attempts to assert its rights over the GIF image compression standard. The JPEG committee investigated the patent claims in 2002 and were of the opinion that they were invalidated by
prior art Prior art (also known as state of the art or background art) is a concept in patent law used to determine the patentability of an invention, in particular whether an invention meets the Novelty (patent), novelty and the inventive step or non-obvio ...
, a view shared by various experts. By the time Chen had filed his patent for a DCT-based image compression algorithm with Klenke in 1986, most of what would later become the JPEG standard had already been formulated in prior literature. JPEG representative Richard Clark also claimed that Chen himself sat in one of the JPEG committees, but Forgent denied this claim. Between 2002 and 2004, Forgent was able to obtain about US$105 million by licensing their patent to some 30 companies. In April 2004, Forgent sued 31 other companies to enforce further license payments. In July of the same year, a consortium of 21 large computer companies filed a countersuit, with the goal of invalidating the patent. In addition, Microsoft launched a separate lawsuit against Forgent in April 2005. In February 2006, the
United States Patent and Trademark Office The United States Patent and Trademark Office (USPTO) is an agency in the U.S. Department of Commerce that issues patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using ...
agreed to re-examine Forgent's JPEG patent at the request of the
Public Patent Foundation In public relations Public relations (PR) is the practice of deliberately managing the release and spread of information between an individual or an organization (such as a business, government agency, or a nonprofit organization) and the ...
. On May 26, 2006 the USPTO found the patent invalid based on
prior art Prior art (also known as state of the art or background art) is a concept in patent law used to determine the patentability of an invention, in particular whether an invention meets the Novelty (patent), novelty and the inventive step or non-obvio ...
. The USPTO also found that Forgent knew about the
prior art Prior art (also known as state of the art or background art) is a concept in patent law used to determine the patentability of an invention, in particular whether an invention meets the Novelty (patent), novelty and the inventive step or non-obvio ...
, yet it intentionally avoided telling the Patent Office. This makes any appeal to reinstate the patent highly unlikely to succeed. Forgent also possesses a similar patent granted by the
European Patent Office The European Patent Office (EPO) is one of the two organs of the European Patent Organisation The European Patent Organisation (sometimes abbreviated EPOrg in order to distinguish it from the European Patent Office, one of the two organs of the ...
in 1994, though it is unclear how enforceable it is. As of October 27, 2006, the U.S. patent's 20-year term appears to have expired, and in November 2006, Forgent agreed to abandon enforcement of patent claims against use of the JPEG standard. The JPEG committee has as one of its explicit goals that their standards (in particular their baseline methods) be implementable without payment of license fees, and they have secured appropriate license rights for their
JPEG 2000 JPEG 2000 (JP2) is an image compression Image compression is a type of data compression In signal processing, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original r ...
standard from over 20 large organizations. Beginning in August 2007, another company, Global Patent Holdings, LLC claimed that its patent () issued in 1993, is infringed by the downloading of JPEG images on either a website or through e-mail. If not invalidated, this patent could apply to any website that displays JPEG images. The patent was under reexamination by the U.S. Patent and Trademark Office from 2000-2007; in July 2007, the Patent Office revoked all of the original claims of the patent but found that an additional claim proposed by Global Patent Holdings (claim 17) was valid.Ex Parte Reexamination Certificate for U.S. Patent No. 5,253,341
Global Patent Holdings then filed a number of lawsuits based on claim 17 of its patent. In its first two lawsuits following the reexamination, both filed in Chicago, Illinois, Global Patent Holdings sued the
Green Bay Packers The Green Bay Packers are a professional American football American football, referred to simply as football in the United States and Canada and also known as gridiron, is a team sport A team sport includes any sport Spo ...

Green Bay Packers
,
CDW CDW Corporation, headquartered in Lincolnshire, Illinois Lincolnshire is a village in Vernon Township, Lake County, Illinois, Lake County, in the United States of America, U.S. state of Illinois. The village is a northern suburb of Chicago. T ...
,
Motorola Motorola, Inc. () was an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational sta ...

Motorola
,
Apple An apple is an edible fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this fie ...
,
Orbitz Orbitz.com is a travel fare aggregator website and travel metasearch engine A metasearch engine (or search aggregator) is an online Information retrieval tool that uses the data of a web search engine to produce its own results. Metasearch ...
,
Officemax OfficeMax is an American office supplies Office supplies are consumables Consumables (also known as consumable goods, non-durable goods, or soft goods) are goods that are intended to be consumed. People have, for example, always consumed foo ...
,
Caterpillar Caterpillars ( ) are the larval stage A larva (plural larvae ) is a distinct juvenile form many animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Anim ...
,
Kraft The second incarnation of Kraft Foods (legal name Kraft Foods Group) is an American food manufacturing and processing , split from in 2012 and headquartered in . It became part of in 2015. A merger with Heinz, arranged by Heinz owners and ...

Kraft
and
Peapod Peapod Online Grocer (US), LLC is an American online grocer In computer technology and telecommunications Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers ...
as defendants. A third lawsuit was filed on December 5, 2007 in South Florida against
ADT Security Services ADT Inc., formerly The ADT Corporation, is an American company that provides residential, small and large business electronic security, fire protection, and other related alarm An alarm device is a mechanism that gives an audible, visual o ...
,
AutoNation AutoNation is an American automotive retailer based in Fort Lauderdale which provides new and pre-owned vehicles and associated services in the United States. The company was founded by Wayne Huizenga Harry Wayne Huizenga Sr. (; December 29, 1 ...
, Florida Crystals Corp., HearUSA, MovieTickets.com, Ocwen Financial Corp. and
Tire KingdomTire Kingdom is a large American tire store chain located primarily in the southern part of the United States. In 2000, it became a subsidiary of TBC Corporation. Background Tire Kingdom was founded by Chuck Curcio in Florida in 1972, starting with ...
, and a fourth lawsuit on January 8, 2008 in South Florida against the
Boca Raton Resort & Club The Boca Raton Resort & Club, located at 501 East Camino Real, Boca Raton, Florida, is one of the premier resort destinations and private club facilities in the United States. The resort, which was founded in 1926, today comprises 1,047 hotel room ...
. A fifth lawsuit was filed against Global Patent Holdings in Nevada. That lawsuit was filed by
Zappos.com Zappos.com is an American online shoe and clothing retailer based in Las Vegas, Nevada, United States. The company was founded in 1999 by Nick Swinmurn and launched under the domain name Shoesite.com. In July 2009, Amazon (company), Amazon acqu ...
, Inc., which was allegedly threatened by Global Patent Holdings, and sought a judicial declaration that the '341 patent is invalid and not infringed. Global Patent Holdings had also used the '341 patent to sue or threaten outspoken critics of broad software patents, including Gregory Aharonian and the anonymous operator of a website blog known as the " Patent Troll Tracker." On December 21, 2007, patent lawyer Vernon Francissen of Chicago asked the U.S. Patent and Trademark Office to reexamine the sole remaining claim of the '341 patent on the basis of new prior art. On March 5, 2008, the U.S. Patent and Trademark Office agreed to reexamine the '341 patent, finding that the new prior art raised substantial new questions regarding the patent's validity. U.S. Patent Office – Granting Reexamination on 5,253,341 C1 In light of the reexamination, the accused infringers in four of the five pending lawsuits have filed motions to suspend (stay) their cases until completion of the U.S. Patent and Trademark Office's review of the '341 patent. On April 23, 2008, a judge presiding over the two lawsuits in Chicago, Illinois granted the motions in those cases. On July 22, 2008, the Patent Office issued the first "Office Action" of the second reexamination, finding the claim invalid based on nineteen separate grounds. On Nov. 24, 2009, a Reexamination Certificate was issued cancelling all claims. Beginning in 2011 and continuing as of early 2013, an entity known as Princeton Digital Image Corporation, based in Eastern Texas, began suing large numbers of companies for alleged infringement of . Princeton claims that the JPEG image compression standard infringes the '056 patent and has sued large numbers of websites, retailers, camera and device manufacturers and resellers. The patent was originally owned and assigned to General Electric. The patent expired in December 2007, but Princeton has sued large numbers of companies for "past infringement" of this patent. (Under U.S. patent laws, a patent owner can sue for "past infringement" up to six years before the filing of a lawsuit, so Princeton could theoretically have continued suing companies until December 2013.) As of March 2013, Princeton had suits pending in New York and Delaware against more than 55 companies. General Electric's involvement in the suit is unknown, although court records indicate that it assigned the patent to Princeton in 2009 and retains certain rights in the patent.


Typical usage

The JPEG compression algorithm operates at its best on photographs and paintings of realistic scenes with smooth variations of tone and color. For web usage, where reducing the amount of data used for an image is important for responsive presentation, JPEG's compression benefits make JPEG popular. JPEG/
Exif Exchangeable image file format (officially Exif, according to JEIDA/JEITA/CIPA specifications) is a standard that specifies the formats for image File:TEIDE.JPG, An Synthetic aperture radar, SAR radar imaging, radar image acquired by the S ...
is also the most common format saved by digital cameras. However, JPEG is not well suited for line drawings and other textual or iconic graphics, where the sharp contrasts between adjacent pixels can cause noticeable artifacts. Such images are better saved in a such as
TIFF Tag Image File Format, abbreviated TIFF or TIF, is an image file format for storing raster graphics images, popular among graphic artists, the publishing industry, and photographers. TIFF is widely supported by image scanner, scanning, FAX, faxi ...

TIFF
,
GIF The Graphics Interchange Format (GIF; or , see pronunciation) is a bitmap In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algor ...
, PNG, or a
raw image format A camera raw image file contains minimally processed data from the image sensor of either a digital camera, a motion picture film scanner, or other image scanner. Raw files are named so because they are not yet processed and therefore are not ...
. The JPEG standard includes a lossless coding mode, but that mode is not supported in most products. As the typical use of JPEG is a
lossy compression In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...
method, which reduces the image fidelity, it is inappropriate for exact reproduction of imaging data (such as some scientific and medical imaging applications and certain technical
image processing Digital image processing is the use of a digital computer A computer is a machine A machine is a man-made device that uses power to apply forces and control movement to perform an action. Machines can be driven by animals and people ...
work). JPEG is also not well suited to files that will undergo multiple edits, as some image quality is lost each time the image is recompressed, particularly if the image is cropped or shifted, or if encoding parameters are changed – see digital generation loss for details. To prevent image information loss during sequential and repetitive editing, the first edit can be saved in a lossless format, subsequently edited in that format, then finally published as JPEG for distribution.


JPEG compression

JPEG uses a lossy form of compression based on the
discrete cosine transform A discrete cosine transform (DCT) expresses a finite sequence of data points In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics ...
(DCT). This mathematical operation converts each frame/field of the video source from the spatial (2D) domain into the frequency domain (a.k.a. transform domain). A perceptual model based loosely on the human psychovisual system discards high-frequency information, i.e. sharp transitions in intensity, and color hue. In the transform domain, the process of reducing information is called quantization. In simpler terms, quantization is a method for optimally reducing a large number scale (with different occurrences of each number) into a smaller one, and the transform-domain is a convenient representation of the image because the high-frequency coefficients, which contribute less to the overall picture than other coefficients, are characteristically small-values with high compressibility. The quantized coefficients are then sequenced and losslessly packed into the output bitstream. Nearly all software implementations of JPEG permit user control over the compression ratio (as well as other optional parameters), allowing the user to trade off picture-quality for smaller file size. In embedded applications (such as miniDV, which uses a similar DCT-compression scheme), the parameters are pre-selected and fixed for the application. The compression method is usually
lossy In information technology, lossy compression or irreversible compression is the class of data compression, data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to r ...
, meaning that some original image information is lost and cannot be restored, possibly affecting image quality. There is an optional
lossless Lossless compression is a class of data compression In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image ...
mode defined in the JPEG standard. However, this mode is not widely supported in products. There is also an
interlaced Interlaced video (also known as interlaced scan) is a technique for doubling the perceived frame rate of a video display without consuming extra Bandwidth (signal processing), bandwidth. The interlaced signal contains two field (video), fields of ...
''progressive'' JPEG format, in which data is compressed in multiple passes of progressively higher detail. This is ideal for large images that will be displayed while downloading over a slow connection, allowing a reasonable preview after receiving only a portion of the data. However, support for progressive JPEGs is not universal. When progressive JPEGs are received by programs that do not support them (such as versions of
Internet Explorer Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, (from August 16, 1995 to March 30, 2021) commonly abbreviated IE or MSIE) is a discontinued series of graphical user interface, graphical web browsers develo ...
before
Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on July 22, 2009, and became generally available on October 22, ...
) the software displays the image only after it has been completely downloaded. There are also many medical imaging, traffic and camera applications that create and process 12-bit JPEG images both grayscale and color. 12-bit JPEG format is included in an Extended part of the JPEG specification. The libjpeg codec supports 12-bit JPEG and there even exists a high-performance version.


Lossless editing

A number of alterations to a JPEG image can be performed losslessly (that is, without recompression and the associated quality loss) as long as the image size is a multiple of 1 MCU block (Minimum Coded Unit) (usually 16 pixels in both directions, for 4:2:0
chroma subsampling Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information Information is processed, organised and structured data. It provides context for data and enables decision making process. For examp ...
). Utilities that implement this include: * jpegtran and its GUI, Jpegcrop. *
IrfanView IrfanView () is an image viewer, editor, organiser and converter program for Microsoft Windows. It can also play video and audio files, and has some image creation and painting capabilities. IrfanView is free for non-commercial use; commercial u ...

IrfanView
using "JPG Lossless Crop (PlugIn)" and "JPG Lossless Rotation (PlugIn)", which require installing the JPG_TRANSFORM plugin. *
FastStone Image Viewer FastStone Image Viewer is an image viewer and image organizer, organizer for Microsoft Windows, provided free of charge for personal and educational use, . The program also includes basic image editing tools. Features Highlights: *Relatively fas ...
using "Lossless Crop to File" and "JPEG Lossless Rotate". * XnViewMP using "JPEG lossless transformations". *
ACDSee ACDSee is an image organizer An image organizer or image management application is application software focused on organising digital images. Image organizers represent one kind of desktop organizer software applications. Image organizer software ...
supports lossless rotation (but not lossless cropping) with its "Force lossless JPEG operations" option. Blocks can be rotated in 90-degree increments, flipped in the horizontal, vertical and diagonal axes and moved about in the image. Not all blocks from the original image need to be used in the modified one. The top and left edge of a JPEG image must lie on an 8 × 8 pixel block boundary, but the bottom and right edge need not do so. This limits the possible lossless crop operations, and also prevents flips and rotations of an image whose bottom or right edge does not lie on a block boundary for all channels (because the edge would end up on top or left, where – as aforementioned – a block boundary is obligatory). Rotations where the image is not a multiple of 8 or 16, which value depends upon the chroma subsampling, are not lossless. Rotating such an image causes the blocks to be recomputed which results in loss of quality. When using lossless cropping, if the bottom or right side of the crop region is not on a block boundary, then the rest of the data from the partially used blocks will still be present in the cropped file and can be recovered. It is also possible to transform between baseline and progressive formats without any loss of quality, since the only difference is the order in which the coefficients are placed in the file. Furthermore, several JPEG images can be losslessly joined together, as long as they were saved with the same quality and the edges coincide with block boundaries.


JPEG files

The
file format A file format is a standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metrology), an object that bears ...
known as "JPEG Interchange Format" (JIF) is specified in Annex B of the standard. However, this "pure" file format is rarely used, primarily because of the difficulty of programming encoders and decoders that fully implement all aspects of the standard and because of certain shortcomings of the standard: * Color space definition * Component sub-sampling registration * Pixel aspect ratio definition. Several additional standards have evolved to address these issues. The first of these, released in 1992, was the
JPEG File Interchange Format The JPEG File Interchange Format (JFIF) is an image file format Image file formats are standardized means of organizing and storing digital image A digital image is an image An SAR radar imaging, radar image acquired by the SIR-C/X-SAR ...
(or JFIF), followed in recent years by
Exchangeable image file format Exchangeable image file format (officially Exif, according to JEIDA/JEITA/CIPA specifications) is a standard that specifies the formats for images, sound In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (e ...
(Exif) and
ICC ICC may refer to: Buildings * International Commerce Centre, a skyscraper in Hong Kong * International Commercial Center, a skyscraper in Ulaanbaatar, Mongolia * International Convention Centre (disambiguation), any of several convention centers * ...
color profiles. Both of these formats use the actual JIF byte layout, consisting of different ''markers'', but in addition, employ one of the JIF standard's extension points, namely the ''application markers'': JFIF uses APP0, while Exif uses APP1. Within these segments of the file that were left for future use in the JIF standard and are not read by it, these standards add specific metadata. Thus, in some ways, JFIF is a cut-down version of the JIF standard in that it specifies certain constraints (such as not allowing all the different encoding modes), while in other ways, it is an extension of JIF due to the added metadata. The documentation for the original JFIF standard states: :''JPEG File Interchange Format is a minimal file format which enables JPEG bitstreams to be exchanged between a wide variety of platforms and applications. This minimal format does not include any of the advanced features found in the TIFF JPEG specification or any application specific file format. Nor should it, for the only purpose of this simplified format is to allow the exchange of JPEG compressed images.'' Image files that employ JPEG compression are commonly called "JPEG files", and are stored in variants of the JIF image format. Most image capture devices (such as digital cameras) that output JPEG are actually creating files in the
Exif Exchangeable image file format (officially Exif, according to JEIDA/JEITA/CIPA specifications) is a standard that specifies the formats for image File:TEIDE.JPG, An Synthetic aperture radar, SAR radar imaging, radar image acquired by the S ...
format, the format that the camera industry has standardized on for metadata interchange. On the other hand, since the Exif standard does not allow color profiles, most image editing software stores JPEG in
JFIF The JPEG File Interchange Format (JFIF) is an standard published as Recommendation T.871 and 10918-5. It defines supplementary specifications for the that contains the image data encoded with the algorithm. The base specifications for a JPEG c ...
format, and also includes the APP1 segment from the Exif file to include the metadata in an almost-compliant way; the JFIF standard is interpreted somewhat flexibly. Strictly speaking, the JFIF and Exif standards are incompatible, because each specifies that its marker segment (APP0 or APP1, respectively) appear first. In practice, most JPEG files contain a JFIF marker segment that precedes the Exif header. This allows older readers to correctly handle the older format JFIF segment, while newer readers also decode the following Exif segment, being less strict about requiring it to appear first.


JPEG filename extensions

The most common
filename extension A filename extension, file extension or file type is an identifier specified as a suffix to the name A name is a term used for identification by an external observer. They can identify a class or category of things, or a single thing, either un ...
s for files employing JPEG compression are .jpg and .jpeg, though .jpe, .jfif and .jif are also used. It is also possible for JPEG data to be embedded in other file types –
TIFF Tag Image File Format, abbreviated TIFF or TIF, is an image file format for storing raster graphics images, popular among graphic artists, the publishing industry, and photographers. TIFF is widely supported by image scanner, scanning, FAX, faxi ...
encoded files often embed a JPEG image as a
thumbnail Thumbnails (/ˈθʌmneɪl/) are reduced-size versions of pictures or video Video is an electronic Electronic may refer to: *Electronics Electronics comprises the physics, engineering, technology and applications that deal with the ...

thumbnail
of the main image; and
MP3 MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio Digital audio is a representation of sound recorded in, or converted into, Digital signal (signal processing), digital form. In digital a ...

MP3
files can contain a JPEG of
cover art Cover art is a type of artwork presented as an illustration An illustration is a decoration, interpretation or visual explanation of a text, concept or process, designed for integration in print and digital published media, such as posters, fl ...
in the
ID3v2 ID3 is a metadata Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive metadata ...
tag.


Color profile

Many JPEG files embed an ICC color profile (
color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of color -- whether such representation entails an analog signal, analog or a ...
). Commonly used color profiles include
sRGB sRGB is a standard RGB (red, green, blue) color space that HP and Microsoft Microsoft Corporation is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countr ...
and
Adobe RGB The Adobe RGB (1998) color space or opRGB is a color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of color -- whe ...
. Because these color spaces use a non-linear transformation, the
dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lem ...
of an 8-bit JPEG file is about 11 stops; see
gamma curve Gamma correction or gamma is a nonlinear operation used to encode and decode luminance Luminance is a Photometry (optics), photometric measure of the luminous intensity per units of measurement, unit area of light travelling in a given direction ...
.


Syntax and structure

A JPEG image consists of a sequence of ''segments'', each beginning with a ''marker'', each of which begins with a 0xFF byte, followed by a byte indicating what kind of marker it is. Some markers consist of just those two bytes; others are followed by two bytes (high then low), indicating the length of marker-specific payload data that follows. (The length includes the two bytes for the length, but not the two bytes for the marker.) Some markers are followed by entropy-coded data; the length of such a marker does not include the entropy-coded data. Note that consecutive 0xFF bytes are used as fill bytes for
padding Padding is thin cushioned material sometimes added to clothes. Padding may also be referred to as batting when used as a layer in lining quilts or as a packaging or stuffing material. When padding is used in clothes, it is often done in an attempt ...
purposes, although this fill byte padding should only ever take place for markers immediately following entropy-coded scan data (see JPEG specification section B.1.1.2 and E.1.2 for details; specifically "In all cases where markers are appended after the compressed data, optional 0xFF fill bytes may precede the marker"). Within the entropy-coded data, after any 0xFF byte, a 0x00 byte is inserted by the encoder before the next byte, so that there does not appear to be a marker where none is intended, preventing framing errors. Decoders must skip this 0x00 byte. This technique, called byte stuffing (see JPEG specification section F.1.2.3), is only applied to the entropy-coded data, not to marker payload data. Note however that entropy-coded data has a few markers of its own; specifically the Reset markers (0xD0 through 0xD7), which are used to isolate independent chunks of entropy-coded data to allow parallel decoding, and encoders are free to insert these Reset markers at regular intervals (although not all encoders do this). There are other ''Start Of Frame'' markers that introduce other kinds of JPEG encodings. Since several vendors might use the same APP''n'' marker type, application-specific markers often begin with a standard or vendor name (e.g., "Exif" or "Adobe") or some other identifying string. At a restart marker, block-to-block predictor variables are reset, and the bitstream is synchronized to a byte boundary. Restart markers provide means for recovery after bitstream error, such as transmission over an unreliable network or file corruption. Since the runs of macroblocks between restart markers may be independently decoded, these runs may be decoded in parallel.


JPEG codec example

Although a JPEG file can be encoded in various ways, most commonly it is done with JFIF encoding. The encoding process consists of several steps: # The representation of the colors in the image is converted from RGB color model, RGB to YCbCr, , consisting of one Luma (video), luma component (Y'), representing brightness, and two chrominance, chroma components, (CB and CR), representing color. This step is sometimes skipped. # The resolution of the chroma data is reduced, usually by a factor of 2 or 3. This reflects the fact that the eye is less sensitive to fine color details than to fine brightness details. # The image is split into blocks of 8×8 pixels, and for each block, each of the Y, CB, and CR data undergoes the
discrete cosine transform A discrete cosine transform (DCT) expresses a finite sequence of data points In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics ...
(DCT). A DCT is similar to a Fourier transform in the sense that it produces a kind of spatial frequency spectrum. # The amplitudes of the frequency components are Quantization (image processing), quantized. Human vision is much more sensitive to small variations in color or brightness over large areas than to the strength of high-frequency brightness variations. Therefore, the magnitudes of the high-frequency components are stored with a lower accuracy than the low-frequency components. The quality setting of the encoder (for example 50 or 95 on a scale of 0–100 in the Independent JPEG Group's library) affects to what extent the resolution of each frequency component is reduced. If an excessively low quality setting is used, the high-frequency components are discarded altogether. # The resulting data for all 8×8 blocks is further compressed with a lossless algorithm, a variant of Huffman encoding. The decoding process reverses these steps, except the ''quantization'' because it is irreversible. In the remainder of this section, the encoding and decoding processes are described in more detail.


Encoding

Many of the options in the JPEG standard are not commonly used, and as mentioned above, most image software uses the simpler JFIF format when creating a JPEG file, which among other things specifies the encoding method. Here is a brief description of one of the more common methods of encoding when applied to an input that has 24 bits per pixel (eight each of RGB color model, red, green, and blue). This particular option is a lossy data compression method.


Color space transformation

First, the image should be converted from RGB color model, RGB into a different
color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of color -- whether such representation entails an analog signal, analog or a ...
called YCbCr, (or, informally, YCbCr). It has three components Y', CB and CR: the Y' component represents the brightness of a pixel, and the CB and CR components represent the chrominance (split into blue and red components). This is basically the same color space as used by digital television, digital color television as well as digital video including DVD Video, video DVDs, and is similar to the way color is represented in analog PAL video and Multiplexed Analogue Components, MAC (but not by analog NTSC, which uses the YIQ color space). The color space conversion allows greater compression without a significant effect on perceptual image quality (or greater perceptual image quality for the same compression). The compression is more efficient because the brightness information, which is more important to the eventual perceptual quality of the image, is confined to a single channel. This more closely corresponds to the perception of color in the human visual system. The color transformation also improves compression by statistical decorrelation. A particular conversion to is specified in the JFIF standard, and should be performed for the resulting JPEG file to have maximum compatibility. However, some JPEG implementations in "highest quality" mode do not apply this step and instead keep the color information in the RGB color model, where the image is stored in separate channels for red, green and blue brightness components. This results in less efficient compression, and would not likely be used when file size is especially important.


Downsampling

Due to the densities of color- and brightness-sensitive receptors in the human eye, humans can see considerably more fine detail in the brightness of an image (the Y' component) than in the hue and color saturation of an image (the Cb and Cr components). Using this knowledge, encoders can be designed to compress images more efficiently. The transformation into the YCbCr, color model enables the next usual step, which is to reduce the spatial resolution of the Cb and Cr components (called "downsampling" or "
chroma subsampling Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information Information is processed, organised and structured data. It provides context for data and enables decision making process. For examp ...
"). The ratios at which the downsampling is ordinarily done for JPEG images are YUV 4:4:4, 4:4:4 (no downsampling), YUV 4:2:2, 4:2:2 (reduction by a factor of 2 in the horizontal direction), or (most commonly) YUV 4:2:0, 4:2:0 (reduction by a factor of 2 in both the horizontal and vertical directions). For the rest of the compression process, Y', Cb and Cr are processed separately and in a very similar manner.


Block splitting

After Chroma Subsampling, subsampling, each Channel (digital image), channel must be split into 8×8 blocks. Depending on chroma subsampling, this yields Minimum Coded Unit (MCU) blocks of size 8×8 (4:4:4 – no subsampling), 16×8 (4:2:2), or most commonly 16×16 (4:2:0). In video compression MCUs are called macroblocks. If the data for a channel does not represent an integer number of blocks then the encoder must fill the remaining area of the incomplete blocks with some form of dummy data. Filling the edges with a fixed color (for example, black) can create ringing artifacts along the visible part of the border; repeating the edge pixels is a common technique that reduces (but does not necessarily completely eliminate) such artifacts, and more sophisticated border filling techniques can also be applied.


Discrete cosine transform

Next, each 8×8 block of each component (Y, Cb, Cr) is converted to a frequency-domain representation, using a normalized, two-dimensional type-II
discrete cosine transform A discrete cosine transform (DCT) expresses a finite sequence of data points In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics ...
(DCT), see Citation 1 in Discrete cosine transform#Citations, discrete cosine transform. The DCT is sometimes referred to as "type-II DCT" in the context of a family of transforms as in Discrete cosine transform#DCT-II, discrete cosine transform, and the corresponding inverse (IDCT) is denoted as "type-III DCT". As an example, one such 8×8 8-bit subimage might be: : \left[ \begin 52 & 55 & 61 & 66 & 70 & 61 & 64 & 73 \\ 63 & 59 & 55 & 90 & 109 & 85 & 69 & 72 \\ 62 & 59 & 68 & 113 & 144 & 104 & 66 & 73 \\ 63 & 58 & 71 & 122 & 154 & 106 & 70 & 69 \\ 67 & 61 & 68 & 104 & 126 & 88 & 68 & 70 \\ 79 & 65 & 60 & 70 & 77 & 68 & 58 & 75 \\ 85 & 71 & 64 & 59 & 55 & 61 & 65 & 83 \\ 87 & 79 & 69 & 68 & 65 & 76 & 78 & 94 \end \right]. Before computing the DCT of the 8×8 block, its values are shifted from a positive range to one centered on zero. For an 8-bit image, each entry in the original block falls in the range [0, 255]. The midpoint of the range (in this case, the value 128) is subtracted from each entry to produce a data range that is centered on zero, so that the modified range is [-128, 127]. This step reduces the dynamic range requirements in the DCT processing stage that follows. This step results in the following values: :g= \begin x \\ \longrightarrow \\ \left[ \begin -76 & -73 & -67 & -62 & -58 & -67 & -64 & -55 \\ -65 & -69 & -73 & -38 & -19 & -43 & -59 & -56 \\ -66 & -69 & -60 & -15 & 16 & -24 & -62 & -55 \\ -65 & -70 & -57 & -6 & 26 & -22 & -58 & -59 \\ -61 & -67 & -60 & -24 & -2 & -40 & -60 & -58 \\ -49 & -63 & -68 & -58 & -51 & -60 & -70 & -53 \\ -43 & -57 & -64 & -69 & -73 & -67 & -63 & -45 \\ -41 & -49 & -59 & -60 & -63 & -52 & -50 & -34 \end \right] \end \Bigg\downarrow y. The next step is to take the two-dimensional DCT, which is given by: :\ G_ = \frac \alpha(u) \alpha(v) \sum_^7 \sum_^7 g_ \cos \left[\frac \right] \cos \left[\frac \right] where * \ u is the horizontal spatial frequency, for the integers \ 0 \leq u < 8. * \ v is the vertical spatial frequency, for the integers \ 0 \leq v < 8. * \alpha(u) = \begin \frac, & \mboxu=0 \\ 1, & \mbox \end is a normalizing scale factor to make the transformation orthonormal * \ g_ is the pixel value at coordinates \ (x,y) * \ G_ is the DCT coefficient at coordinates \ (u,v). If we perform this transformation on our matrix above, we get the following (rounded to the nearest two digits beyond the decimal point): :G= \begin u \\ \longrightarrow \\ \left[ \begin -415.38 & -30.19 & -61.20 & 27.24 & 56.12 & -20.10 & -2.39 & 0.46 \\ 4.47 & -21.86 & -60.76 & 10.25 & 13.15 & -7.09 & -8.54 & 4.88 \\ -46.83 & 7.37 & 77.13 & -24.56 & -28.91 & 9.93 & 5.42 & -5.65 \\ -48.53 & 12.07 & 34.10 & -14.76 & -10.24 & 6.30 & 1.83 & 1.95 \\ 12.12 & -6.55 & -13.20 & -3.95 & -1.87 & 1.75 & -2.79 & 3.14 \\ -7.73 & 2.91 & 2.38 & -5.94 & -2.38 & 0.94 & 4.30 & 1.85 \\ -1.03 & 0.18 & 0.42 & -2.42 & -0.88 & -3.02 & 4.12 & -0.66 \\ -0.17 & 0.14 & -1.07 & -4.19 & -1.17 & -0.10 & 0.50 & 1.68 \end \right] \end \Bigg\downarrow v. Note the top-left corner entry with the rather large magnitude. This is the DC coefficient (also called the constant component), which defines the basic hue for the entire block. The remaining 63 coefficients are the AC coefficients (also called the alternating components). The advantage of the DCT is its tendency to aggregate most of the signal in one corner of the result, as may be seen above. The quantization step to follow accentuates this effect while simultaneously reducing the overall size of the DCT coefficients, resulting in a signal that is easy to compress efficiently in the entropy stage. The DCT temporarily increases the bit-depth of the data, since the DCT coefficients of an 8-bit/component image take up to 11 or more bits (depending on fidelity of the DCT calculation) to store. This may force the codec to temporarily use 16-bit numbers to hold these coefficients, doubling the size of the image representation at this point; these values are typically reduced back to 8-bit values by the quantization step. The temporary increase in size at this stage is not a performance concern for most JPEG implementations, since typically only a very small part of the image is stored in full DCT form at any given time during the image encoding or decoding process.


Quantization

The human eye is good at seeing small differences in brightness over a relatively large area, but not so good at distinguishing the exact strength of a high frequency brightness variation. This allows one to greatly reduce the amount of information in the high frequency components. This is done by simply dividing each component in the frequency domain by a constant for that component, and then rounding to the nearest integer. This rounding operation is the only lossy operation in the whole process (other than chroma subsampling) if the DCT computation is performed with sufficiently high precision. As a result of this, it is typically the case that many of the higher frequency components are rounded to zero, and many of the rest become small positive or negative numbers, which take many fewer bits to represent. The elements in the quantization matrix control the compression ratio, with larger values producing greater compression. A typical quantization matrix (for a quality of 50% as specified in the original JPEG Standard), is as follows: :Q= \begin 16 & 11 & 10 & 16 & 24 & 40 & 51 & 61 \\ 12 & 12 & 14 & 19 & 26 & 58 & 60 & 55 \\ 14 & 13 & 16 & 24 & 40 & 57 & 69 & 56 \\ 14 & 17 & 22 & 29 & 51 & 87 & 80 & 62 \\ 18 & 22 & 37 & 56 & 68 & 109 & 103 & 77 \\ 24 & 35 & 55 & 64 & 81 & 104 & 113 & 92 \\ 49 & 64 & 78 & 87 & 103 & 121 & 120 & 101 \\ 72 & 92 & 95 & 98 & 112 & 100 & 103 & 99 \end. The quantized DCT coefficients are computed with :B_ = \mathrm \left( \frac \right) \mbox j=0,1,2,\ldots,7; k=0,1,2,\ldots,7 where G is the unquantized DCT coefficients; Q is the quantization matrix above; and B is the quantized DCT coefficients. Using this quantization matrix with the DCT coefficient matrix from above results in: :B= \left[ \begin -26 & -3 & -6 & 2 & 2 & -1 & 0 & 0 \\ 0 & -2 & -4 & 1 & 1 & 0 & 0 & 0 \\ -3 & 1 & 5 & -1 & -1 & 0 & 0 & 0 \\ -3 & 1 & 2 & -1 & 0 & 0 & 0 & 0 \\ 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \end \right]. For example, using −415 (the DC coefficient) and rounding to the nearest integer : \mathrm \left( \frac \right) = \mathrm \left( -25.96 \right) = -26. Notice that most of the higher-frequency elements of the sub-block (i.e., those with an ''x'' or ''y'' spatial frequency greater than 4) are quantized into zero values.


Entropy coding

Entropy coding is a special form of lossless data compression. It involves arranging the image components in a "zigzag" order employing run-length encoding (RLE) algorithm that groups similar frequencies together, inserting length coding zeros, and then using
Huffman coding In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algor ...
on what is left. The JPEG standard also allows, but does not require, decoders to support the use of
arithmetic coding Arithmetic coding is a form of entropy encoding In information theory, an entropy coding (or entropy encoding) is a lossless compression , lossless data compression scheme that is independent of the specific characteristics of the medium. One of ...
, which is mathematically superior to Huffman coding. However, this feature has rarely been used, as it was historically covered by
patent A patent is a type of intellectual property Intellectual property (IP) is a category of property Property is a system of rights that gives people legal control of valuable things, and also refers to the valuable things themselves. Depe ...

patent
s requiring royalty-bearing licenses, and because it is slower to encode and decode compared to Huffman coding. Arithmetic coding typically makes files about 5–7% smaller. The previous quantized DC coefficient is used to predict the current quantized DC coefficient. The difference between the two is encoded rather than the actual value. The encoding of the 63 quantized AC coefficients does not use such prediction differencing. The zigzag sequence for the above quantized coefficients are shown below. (The format shown is just for ease of understanding/viewing.) : If the ''i''-th block is represented by B_i and positions within each block are represented by (p,q) where p = 0, 1, ..., 7 and q = 0, 1, ..., 7, then any coefficient in the DCT image can be represented as B_i (p,q). Thus, in the above scheme, the order of encoding pixels (for the -th block) is B_i (0,0), B_i (0,1), B_i (1,0), B_i (2,0), B_i (1,1), B_i (0,2), B_i (0,3), B_i (1,2) and so on. This encoding mode is called baseline ''sequential'' encoding. Baseline JPEG also supports ''progressive'' encoding. While sequential encoding encodes coefficients of a single block at a time (in a zigzag manner), progressive encoding encodes similar-positioned batch of coefficients of all blocks in one go (called a ''scan''), followed by the next batch of coefficients of all blocks, and so on. For example, if the image is divided into N 8×8 blocks B_0,B_1,B_2,...,B_, then a 3-scan progressive encoding encodes DC component, B_i (0,0) for all blocks, i.e., for all i = 0, 1, 2, ..., N-1, in first scan. This is followed by the second scan which encoding a few more components (assuming four more components, they are B_i (0,1) to B_i (1,1), still in a zigzag manner) coefficients of all blocks (so the sequence is: B_0 (0,1),B_0 (1,0),B_0 (2,0),B_0 (1,1),B_1 (0,1),B_1 (1,0),...,B_N (2,0),B_N (1,1)), followed by all the remained coefficients of all blocks in the last scan. Once all similar-positioned coefficients have been encoded, the next position to be encoded is the one occurring next in the zigzag traversal as indicated in the figure above. It has been found that ''baseline progressive'' JPEG encoding usually gives better compression as compared to ''baseline sequential'' JPEG due to the ability to use different Huffman tables (see below) tailored for different frequencies on each "scan" or "pass" (which includes similar-positioned coefficients), though the difference is not too large. In the rest of the article, it is assumed that the coefficient pattern generated is due to sequential mode. In order to encode the above generated coefficient pattern, JPEG uses Huffman encoding. The JPEG standard provides general-purpose Huffman tables; encoders may also choose to generate Huffman tables optimized for the actual frequency distributions in images being encoded. The process of encoding the zig-zag quantized data begins with a run-length encoding explained below, where: * is the non-zero, quantized AC coefficient. * ''RUNLENGTH'' is the number of zeroes that came before this non-zero AC coefficient. * ''SIZE'' is the number of bits required to represent . * ''AMPLITUDE'' is the bit-representation of . The run-length encoding works by examining each non-zero AC coefficient and determining how many zeroes came before the previous AC coefficient. With this information, two symbols are created: : Both ''RUNLENGTH'' and ''SIZE'' rest on the same byte, meaning that each only contains four bits of information. The higher bits deal with the number of zeroes, while the lower bits denote the number of bits necessary to encode the value of . This has the immediate implication of ''Symbol 1'' being only able store information regarding the first 15 zeroes preceding the non-zero AC coefficient. However, JPEG defines two special Huffman code words. One is for ending the sequence prematurely when the remaining coefficients are zero (called "End-of-Block" or "EOB"), and another when the run of zeroes goes beyond 15 before reaching a non-zero AC coefficient. In such a case where 16 zeroes are encountered before a given non-zero AC coefficient, ''Symbol 1'' is encoded "specially" as: (15, 0)(0). The overall process continues until "EOB" denoted by (0, 0) is reached. With this in mind, the sequence from earlier becomes: :(0, 2)(-3);(1, 2)(-3);(0, 1)(-2);(0, 2)(-6);(0, 1)(2);(0, 1)(-4);(0, 1)(1);(0, 2)(-3);(0, 1)(1);(0, 1)(1); :(0, 2)(5);(0, 1)(1);(0, 1)(2);(0, 1)(-1);(0, 1)(1);(0, 1)(-1);(0, 1)(2);(5, 1)(-1);(0, 1)(-1);(0, 0); (The first value in the matrix, −26, is the DC coefficient; it is not encoded the same way. See above.) From here, frequency calculations are made based on occurrences of the coefficients. In our example block, most of the quantized coefficients are small numbers that are not preceded immediately by a zero coefficient. These more-frequent cases will be represented by shorter code words.


Compression ratio and artifacts

The resulting compression ratio can be varied according to need by being more or less aggressive in the divisors used in the quantization phase. Ten to one compression usually results in an image that cannot be distinguished by eye from the original. A compression ratio of 100:1 is usually possible, but will look distinctly Compression artifact, artifacted compared to the original. The appropriate level of compression depends on the use to which the image will be put. Those who use the
World Wide Web The World Wide Web (WWW), commonly known as the Web, is an information system An information system (IS) is a formal, sociotechnical Sociotechnical systems (STS) in organizational development is an approach to complex organizational ...
may be familiar with the irregularities known as compression artifacts that appear in JPEG images, which may take the form of noise around contrasting edges (especially curves and corners), or "blocky" images. These are due to the quantization step of the JPEG algorithm. They are especially noticeable around sharp corners between contrasting colors (text is a good example, as it contains many such corners). The analogous artifacts in MPEG video are referred to as ''mosquito noise,'' as the resulting "edge busyness" and spurious dots, which change over time, resemble mosquitoes swarming around the object.Phuc-Tue Le Dinh and Jacques Patry
Video compression artifacts and MPEG noise reduction
Video Imaging DesignLine. February 24, 2006. Retrieved May 28, 2009.
These artifacts can be reduced by choosing a lower level of image compression, compression; they may be completely avoided by saving an image using a Lossless data compression, lossless file format, though this will result in a larger file size. The images created with Ray tracing (graphics), ray-tracing programs have noticeable blocky shapes on the terrain. Certain low-intensity compression artifacts might be acceptable when simply viewing the images, but can be emphasized if the image is subsequently processed, usually resulting in unacceptable quality. Consider the example below, demonstrating the effect of lossy compression on an edge detection processing step. Some programs allow the user to vary the amount by which individual blocks are compressed. Stronger compression is applied to areas of the image that show fewer artifacts. This way it is possible to manually reduce JPEG file size with less loss of quality. Since the quantization stage ''always'' results in a loss of information, JPEG standard is always a lossy compression codec. (Information is lost both in quantizing and rounding of the floating-point numbers.) Even if the quantization matrix is a matrix of ones, information will still be lost in the rounding step.


Decoding

Decoding to display the image consists of doing all the above in reverse. Taking the DCT coefficient matrix (after adding the difference of the DC coefficient back in) : \left[ \begin -26 & -3 & -6 & 2 & 2 & -1 & 0 & 0 \\ 0 & -2 & -4 & 1 & 1 & 0 & 0 & 0 \\ -3 & 1 & 5 & -1 & -1 & 0 & 0 & 0 \\ -3 & 1 & 2 & -1 & 0 & 0 & 0 & 0 \\ 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \end \right] and taking the Hadamard product (matrices), entry-for-entry product with the quantization matrix from above results in : \left[ \begin -416 & -33 & -60 & 32 & 48 & -40 & 0 & 0 \\ 0 & -24 & -56 & 19 & 26 & 0 & 0 & 0 \\ -42 & 13 & 80 & -24 & -40 & 0 & 0 & 0 \\ -42 & 17 & 44 & -29 & 0 & 0 & 0 & 0 \\ 18 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \end \right] which closely resembles the original DCT coefficient matrix for the top-left portion. The next step is to take the two-dimensional inverse DCT (a 2D type-III DCT), which is given by: f_ = \frac \sum_^7 \sum_^7 \alpha(u) \alpha(v) F_ \cos \left[\frac \right] \cos \left[\frac \right] where * \ x is the pixel row, for the integers \ 0 \leq x < 8. * \ y is the pixel column, for the integers \ 0 \leq y < 8. * \ \alpha(u) is defined as above, for the integers \ 0 \leq u < 8. * \ F_ is the reconstructed approximate coefficient at coordinates \ (u,v). * \ f_ is the reconstructed pixel value at coordinates \ (x,y) Rounding the output to integer values (since the original had integer values) results in an image with values (still shifted down by 128) : \left[ \begin -66 & -63 & -71 & -68 & -56 & -65 & -68 & -46 \\ -71 & -73 & -72 & -46 & -20 & -41 & -66 & -57 \\ -70 & -78 & -68 & -17 & 20 & -14 & -61 & -63 \\ -63 & -73 & -62 & -8 & 27 & -14 & -60 & -58 \\ -58 & -65 & -61 & -27 & -6 & -40 & -68 & -50 \\ -57 & -57 & -64 & -58 & -48 & -66 & -72 & -47 \\ -53 & -46 & -61 & -74 & -65 & -63 & -62 & -45 \\ -47 & -34 & -53 & -74 & -60 & -47 & -47 & -41 \end \right] and adding 128 to each entry : \left[ \begin 62 & 65 & 57 & 60 & 72 & 63 & 60 & 82 \\ 57 & 55 & 56 & 82 & 108 & 87 & 62 & 71 \\ 58 & 50 & 60 & 111 & 148 & 114 & 67 & 65 \\ 65 & 55 & 66 & 120 & 155 & 114 & 68 & 70 \\ 70 & 63 & 67 & 101 & 122 & 88 & 60 & 78 \\ 71 & 71 & 64 & 70 & 80 & 62 & 56 & 81 \\ 75 & 82 & 67 & 54 & 63 & 65 & 66 & 83 \\ 81 & 94 & 75 & 54 & 68 & 81 & 81 & 87 \end \right]. This is the decompressed subimage. In general, the decompression process may produce values outside the original input range of [0, 255]. If this occurs, the decoder needs to clip the output values so as to keep them within that range to prevent overflow when storing the decompressed image with the original bit depth. The decompressed subimage can be compared to the original subimage (also see images to the right) by taking the difference (original − uncompressed) results in the following error values: : \left[ \begin -10 & -10 & 4 & 6 & -2 & -2 & 4 & -9 \\ 6 & 4 & -1 & 8 & 1 & -2 & 7 & 1 \\ 4 & 9 & 8 & 2 & -4 & -10 & -1 & 8 \\ -2 & 3 & 5 & 2 & -1 & -8 & 2 & -1 \\ -3 & -2 & 1 & 3 & 4 & 0 & 8 & -8 \\ 8 & -6 & -4 & -0 & -3 & 6 & 2 & -6 \\ 10 & -11 & -3 & 5 & -8 & -4 & -1 & -0 \\ 6 & -15 & -6 & 14 & -3 & -5 & -3 & 7 \end \right] with an average absolute error of about 5 values per pixels (i.e., \frac \sum_^7 \sum_^7 , e(x,y), = 4.8750). The error is most noticeable in the bottom-left corner where the bottom-left pixel becomes darker than the pixel to its immediate right.


Required precision

The encoding description in the JPEG standard does not fix the precision needed for the output compressed image. However, the JPEG standard (and the similar MPEG standards) includes some precision requirements for the ''de''coding, including all parts of the decoding process (variable length decoding, inverse DCT, dequantization, renormalization of outputs); the output from the reference algorithm must not exceed: * a maximum of one bit of difference for each pixel component * low mean square error over each 8×8-pixel block * very low mean error over each 8×8-pixel block * very low mean square error over the whole image * extremely low mean error over the whole image These assertions are tested on a large set of randomized input images, to handle the worst cases. The former IEEE 1180–1990 standard contained some similar precision requirements. The precision has a consequence on the implementation of decoders, and it is critical because some encoding processes (notably used for encoding sequences of images like MPEG) need to be able to construct, on the encoder side, a reference decoded image. In order to support 8-bit precision per pixel component output, dequantization and inverse DCT transforms are typically implemented with at least 14-bit precision in optimized decoders.


Effects of JPEG compression

JPEG compression artifacts blend well into photographs with detailed non-uniform textures, allowing higher compression ratios. Notice how a higher compression ratio first affects the high-frequency textures in the upper-left corner of the image, and how the contrasting lines become more fuzzy. The very high compression ratio severely affects the quality of the image, although the overall colors and image form are still recognizable. However, the precision of colors suffer less (for a human eye) than the precision of contours (based on luminance). This justifies the fact that images should be first transformed in a color model separating the luminance from the chromatic information, before subsampling the chromatic planes (which may also use lower quality quantization) in order to preserve the precision of the luminance plane with more information bits.


Sample photographs

For information, the uncompressed 24-bit RGB bitmap image below (73,242 pixels) would require 219,726 bytes (excluding all other information headers). The filesizes indicated below include the internal JPEG information headers and some metadata. For highest quality images (Q=100), about 8.25 bits per color pixel is required. On grayscale images, a minimum of 6.5 bits per pixel is enough (a comparable Q=100 quality color information requires about 25% more encoded bits). The highest quality image below (Q=100) is encoded at nine bits per color pixel, the medium quality image (Q=25) uses one bit per color pixel. For most applications, the quality factor should not go below 0.75 bit per pixel (Q=12.5), as demonstrated by the low quality image. The image at lowest quality uses only 0.13 bit per pixel, and displays very poor color. This is useful when the image will be displayed in a significantly scaled-down size. A method for creating better quantization matrices for a given image quality using PSNR instead of the Q factor is described in Minguillón & Pujol (2001). :: The medium quality photo uses only 4.3% of the storage space required for the uncompressed image, but has little noticeable loss of detail or visible artifacts. However, once a certain threshold of compression is passed, compressed images show increasingly visible defects. See the article on rate–distortion theory for a mathematical explanation of this threshold effect. A particular limitation of JPEG in this regard is its non-overlapped 8×8 block transform structure. More modern designs such as
JPEG 2000 JPEG 2000 (JP2) is an image compression Image compression is a type of data compression In signal processing, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original r ...
and JPEG XR exhibit a more graceful degradation of quality as the bit usage decreases – by using transforms with a larger spatial extent for the lower frequency coefficients and by using overlapping transform basis functions.


Lossless further compression

From 2004 to 2008, new research emerged on ways to further compress the data contained in JPEG images without modifying the represented image.I. Bauermann and E. Steinbacj. Further Lossless Compression of JPEG Images. Proc. of Picture Coding Symposium (PCS 2004), San Francisco, US, December 15–17, 2004.N. Ponomarenko, K. Egiazarian, V. Lukin and J. Astola. Additional Lossless Compression of JPEG Images, Proc. of the 4th Intl. Symposium on Image and Signal Processing and Analysis (ISPA 2005), Zagreb, Croatia, pp. 117–120, September 15–17, 2005.M. Stirner and G. Seelmann. Improved Redundancy Reduction for JPEG Files. Proc. of Picture Coding Symposium (PCS 2007), Lisbon, Portugal, November 7–9, 2007Ichiro Matsuda, Yukio Nomoto, Kei Wakabayashi and Susumu Itoh. Lossless Re-encoding of JPEG images using block-adaptive intra prediction. Proceedings of the 16th European Signal Processing Conference (EUSIPCO 2008). This has applications in scenarios where the original image is only available in JPEG format, and its size needs to be reduced for archiving or transmission. Standard general-purpose compression tools cannot significantly compress JPEG files. Typically, such schemes take advantage of improvements to the naive scheme for coding DCT coefficients, which fails to take into account: * Correlations between magnitudes of adjacent coefficients in the same block; * Correlations between magnitudes of the same coefficient in adjacent blocks; * Correlations between magnitudes of the same coefficient/block in different channels; * The DC coefficients when taken together resemble a downscale version of the original image multiplied by a scaling factor. Well-known schemes for Lossless compression#Graphics, lossless coding of continuous-tone images can be applied, achieving somewhat better compression than the Huffman coded DPCM used in JPEG. Some standard but rarely used options already exist in JPEG to improve the efficiency of coding DCT coefficients: the
arithmetic coding Arithmetic coding is a form of entropy encoding In information theory, an entropy coding (or entropy encoding) is a lossless compression , lossless data compression scheme that is independent of the specific characteristics of the medium. One of ...
option, and the progressive coding option (which produces lower bitrates because values for each coefficient are coded independently, and each coefficient has a significantly different distribution). Modern methods have improved on these techniques by reordering coefficients to group coefficients of larger magnitude together; using adjacent coefficients and blocks to predict new coefficient values; dividing blocks or coefficients up among a small number of independently coded models based on their statistics and adjacent values; and most recently, by decoding blocks, predicting subsequent blocks in the spatial domain, and then encoding these to generate predictions for DCT coefficients. Typically, such methods can compress existing JPEG files between 15 and 25 percent, and for JPEGs compressed at low-quality settings, can produce improvements of up to 65%. A freely available tool called packJPG is based on the 2007 paper "Improved Redundancy Reduction for JPEG Files."


Derived formats for stereoscopic 3D


JPEG Stereoscopic

JPS is a stereoscopic JPEG image used for creating 3D effects from 2D images. It contains two static images, one for the left eye and one for the right eye; encoded as two side-by-side images in a single JPG file. JPEG Stereoscopic (JPS, extension .jps) is a JPEG-based format for stereoscopy, stereoscopic images. It has a range of configurations stored in the JPEG APP3 marker field, but usually contains one image of double width, representing two images of identical size in cross-eyed (i.e. left frame on the right half of the image and vice versa) side-by-side arrangement. This file format can be viewed as a JPEG without any special software, or can be processed for rendering in other modes.


JPEG Multi-Picture Format

JPEG Multi-Picture Format (MPO, extension .mpo) is a JPEG-based format for storing multiple images in a single file. It contains two or more JPEG files concatenated together. It also defines a JPEG APP2 marker segment for image description. Various devices use it to store 3D images, such as Fujifilm FinePix Real 3D W1, HTC Evo 3D, JVC GY-HMZ1U AVCHD/MVC extension camcorder, Nintendo 3DS, Panasonic Lumix DMC-TZ20, Panasonic Lumix DMC-TZ30, DMC-TZ30, Panasonic Lumix DMC-TZ60, DMC-TZ60, DMC-TS4 (FT4), and Sony DSC-HX7V. Other devices use it to store "preview images" that can be displayed on a TV. In the last few years, due to the growing use of stereoscopic images, much effort has been spent by the scientific community to develop algorithms for stereoscopic
image compression Image compression is a type of data compression In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image proc ...
.


Implementations

A very important implementation of a JPEG codec is the free programming library ''libjpeg'' of the Independent JPEG Group. It was first published in 1991 and was key for the success of the standard. This library or a direct derivative of it is used in countless applications. Recent versions introduce proprietary extensions libjpeg#history, which broke ABI compatibility with previous versions. In March 2017, Google released the open source project Guetzli, which trades off a much longer encoding time for smaller file size (similar to what Zopfli does for PNG and other lossless data formats). ISO/IEC Joint Photography Experts Group maintains a reference software implementation which can encode both base JPEG (ISO/IEC 10918-1 and 18477-1) and JPEG XT extensions (ISO/IEC 18477 Parts 2 and 6-9), as well as JPEG-LS (ISO/IEC 14495).


JPEG XT

JPEG XT (ISO/IEC 18477) was published in June 2015; it extends base JPEG format with support for higher integer bit depths (up to 16 bit), high dynamic range imaging and floating-point coding, lossless coding, and alpha channel coding. Extensions are backward compatible with the base JPEG/JFIF file format and 8-bit lossy compressed image. JPEG XT uses an extensible file format based on JFIF. Extension layers are used to modify the JPEG 8-bit base layer and restore the high-resolution image. Existing software is forward compatible and can read the JPEG XT binary stream, though it would only decode the base 8-bit layer.


JPEG XL

Since August 2017, JTC1/SC29/WG1 issued a series of draft calls for proposals on JPEG XLthe next generation image compression standard with substantially better compression efficiency (60% improvement) comparing to JPEG. The standard is expected to exceed the still image compression performance shown by HEVC HM, Daala and WebP, and unlike previous efforts attempting to replace JPEG, to provide lossless more efficient recompression transport and storage option for traditional JPEG images. The core requirements include support for very high-resolution images (at least 40 MP), 8–10 bits per component, RGB/YCbCr/ICtCp color encoding, animated images, alpha channel coding, Rec.709 color space (sRGB) and gamma function (2.4-power), Rec.2100 wide color gamut color space (Rec.2020) and high dynamic range transfer functions (PQ and HLG), and high-quality compression of synthetic images, such as bitmap fonts and gradients. The standard should also offer higher bit depths (12–16 bit integer and floating point), additional color spaces and transfer functions (such as Log C from Arri Alexa, Arri), embedded preview images, lossless alpha channel encoding, image region coding, and low-complexity encoding. Any patented technologies would be licensed on a royalty-free basis. The proposals were submitted by September 2018, leading to a committee draft in July 2019, with current target publication date in October 2019.


See also

* Better Portable Graphics, a format based on intra-frame encoding of the HEVC * C-Cube, an early implementer of JPEG in chip form * Comparison of graphics file formats * Comparison of layout engines (graphics) * Deblocking filter (video), the similar deblocking methods could be applied to JPEG * Design rule for Camera File system (DCF) * File extensions * Graphics editing program * High Efficiency Image File Format, image container format for High Efficiency Video Coding, HEVC and other image coding formats * Lenna (test image), the traditional standard image used to test image processing algorithms * Lossless Image Codec FELICS * Motion JPEG * WebP


References


External links


JPEG Compress Online Tool site

JPEG Standard (JPEG ISO/IEC 10918-1 ITU-T Recommendation T.81)
at W3.org
Official Joint Photographic Experts Group (JPEG) site

JFIF File Format
at W3.org
JPEG viewer in 250 lines of easy to understand Python code

Example images over the full range of quantization levels from 1 to 100
at visengi.com
Public domain JPEG compressor in a single C++ source file, along with a matching decompressor
at code.google.com
JPEG decoder open source code, copyright (C) 1995–1997, Thomas G. Lane
{{DEFAULTSORT:JPEG JPEG, Articles containing video clips Computer-related introductions in 1992 Discovery and invention controversies American inventions Indian inventions Japanese inventions Taiwanese inventions ITU-T recommendations ITU-T Recommendations Series IEC standards ISO standards Lossy compression algorithms Image compression Open formats Raster graphics file formats