libjpeg

libjpegis a freelibrarywithfunctionsfor handling theJPEGimage data format. It implements a JPEGcodec(encoding and decoding) alongside various utilities for handling JPEG data. It is written inCand distributed asfree softwaretogether with itssource codeunder the terms of a custompermissive(BSD-like) free software license, which demandsattribution. The original variant is maintained and published by the Independent JPEG Group (IJG). Meanwhile, there are severalforkswith additional features.

libjpeg

Developer(s)	Independent JPEG Group Guido Vollbeding (maintainer)
Initial release	October 7, 1991(1991-10-07)
Stable release	9f / 14 January 2024(14 January 2024)
Repository	github.com/thorfdbg/libjpeg
Written in	C
Operating system	Cross-platform
Type	library
License	CustomBSD-like (free software)
Website	ijg.org jpegclub.org

JPEGJFIFimages are widely used on the Web. The amount of compression can be adjusted to achieve the desired trade-off between file size and visual quality.

Utilities

The following utility programs are shipped together with libjpeg:

cjpeg and djpeg

for performing conversions between JPEG and some other popular image file formats.

rdjpgcom and wrjpgcom

for inserting and extracting textual comments in JPEG files.

jpegtran

for transformation of existing JPEG files.

jpegtran

jpegtran transforms JPEG data without reencoding
(here with user interfaceCropGUI)

Thecommand-lineprogramjpegtranprovides several features for reformatting and recoding the representation of theDCTcoefficients, for transformation of actual image data and for discarding auxiliary data in JPEG files, respectively. The transformations regarding the representation of the coefficients comprise:

• optimisation of theHuffman codinglayer of a JPEG file to increase compression,
• conversion between progressive and sequential JPEG formats,
• conversion between Huffman andarithmetic codingin theentropy codinglayer.

These transformations are each completely lossless and reversible. The transformations on the image data comprise:

• eliminate non-standard application-specific data inserted by some image programs,
• perform certain transformations on a file, such as:
  • discarding of colour channels (conversion to greyscale),
  • rotating andflippingin steps of 90 degrees,
  • croppingor joining at image block borders (every 8×8 or 16×16 pixels),
  • rescaling.

These arelosslessand reversible only regarding the image data that is kept. Reencoding with repeated lossy quantisation of the image data (generation loss) does not take place.

History

The JPEG implementation of the Independent JPEG Group (IJG) was first publicly released on 7 October 1991 and has been considerably developed since that time. The development was initially mainly done byTom Lane. Theopen-sourceimplementation of the IJG was one of the major open-source packages and was key to the success of the JPEG standard. Many companies incorporated it into a variety of products such as image editors and web browsers.

For version 5, which was released on September 24, 1994, the whole code base was rewritten. It introduced the utility programsrdjpgcomandwrjpgcomfor handling embedded text comments. The version 6 from 2 August 1995 came with support for progressive JPEG and for the first time with the utility programjpegtran.This utility was extended with features to rotate and flip images and grayscale reduction in version 6b.

libjpeg-turbo and descendants

From version 6b of libjpeg of 27 March 1998, Miyasaka Masaru forked a branch namedlibjpeg/SIMD,which included x86 SIMD optimisations. It got substantial contributions from the TigerVNC and the VirtualGL projects in 2009. On that basis the libjpeg-turbo project was created in 2010.

On 4 March 2014, the first version of the filesize-optimising forkMozJPEGwas published. For this version Josh Aas from Mozilla Research reworked thePerlscriptjpegcrushfromx264's main developer Loren Merritt and integrated it into the code base of libjpeg-turbo.

On 10 July 2014, Mozilla released version 2.0, which mainly added trellis quantisation and is now able to reduce the size of baseline JPEGs also.Facebook,Inc. donated60000dollarsfor the development of the next version,andCloudFlareassigned a developer for the improvement of MozJPEG.

In 2019, libjpeg-turbo became the ISO and ITU endorsed reference implementation for the JPEG format.

In April 2024, Google introducedJpegli,a new JPEG coding library that offers enhanced capabilities and a 35% compression ratio improvement at high quality compression settings, while the coding speed is comparable with MozJPEG.

Change in IJG leadership

After 11 years and a change in leadership, the IJG under Guido Vollbeding released new versions of libjpeg (7 through 9), of which each broke ABI compatibility with previous versions.The changes that were held in prospect after the 6x series were not delivered. In version 7, support forarithmetic codingwas introduced, which earlier has been rejected because of thepatentsituation, as well as the crop feature in jpegtran (-crop).

Versions 8 and 9 served basically for the introduction of controversialincompatible format extensions. These are widely regarded as ineffective and inferior to existing, standardised solutions.Their standardisation was rejected after submission to theITU-T.The original organiser Tom Lane and others criticize these changes as a break from the goals of the IJG.

Versions

Version	Released	New features
ITU T.81 JPEG Compatible
Old version, no longer maintained:1	1991	First release Baseline or optimized JPEG GIF or PPM output
Old version, no longer maintained:2	1991	Internal improvements More input/output formats
Old version, no longer maintained:3	1992	Internal and image quality improvements
Old version, no longer maintained:4	1992	Internal and speed improvements
Old version, no longer maintained:4a	1993-02-18
Old version, no longer maintained:5	1994-09-24	Internal improvements and revised API
Old version, no longer maintained:5a	1994-12-07
Old version, no longer maintained:5b	1995-03-15
Old version, no longer maintained:6	1995-08-02	Progressive JPEG jpegtran (convert between baseline and progressive)
Old version, no longer maintained:6a	1996-02-07
Old version, yet still maintained:6b	1998-03-27	jpegtran extended to lossless rotate (used bylibjpeg-turbo,MozJPEGandJpegli)
Old version, no longer maintained:7	2009-06-27	jpegtran extended to lossless crop T.851 Arithmetic Coding Scaled DCT
Proprietary non-compatible extensions
Old version, no longer maintained:8	2010-01-10	SmartScale extension (ITU rejected) jpegtran extended to use SmartScale Internal fixes
Old version, no longer maintained:8a	2010-02-28	RGBA
Old version, no longer maintained:8b	2010-05-16	Memory corruption & build fixes
Old version, no longer maintained:8c	2011-01-16	Option for selecting DCT block size (SmartScale)
Old version, no longer maintained:8d	2012-01-15	RGB JPEG (no color transform to YCbCr)
Old version, no longer maintained:9	2013-01-13	YCoCgcolor Lossless compression (1x1 DCT)
Old version, no longer maintained:9a	2014-01-19	"JFIFv2 "scRGBWide color gamut (standard unknown) 8-12 bit color (standardJPEG)
Old version, no longer maintained:9b	2016-01-17	Computation improvements
Old version, no longer maintained:9c	2018-01-14	jpegtran -wipe
Old version, no longer maintained:9d	2020-01-12	Code cleanup Huffman optimization x64 support (MSVC) jpegtran -drop
Old version, no longer maintained:9e	2022-01-16	ARM and ARM64 support (MSVC)
Current stable version:9f	2024-01-14	ARM64EC support (MSVC) Xcode build system C++Builder/RAD Studio build system

Legend:	Old version, not maintained	Old version, still maintained	Current stable version	Latest preview version	Future release

Forks

Well-known forks are libjpeg-turbo, which optimises for speed of execution, and MozJPEG, which optimises for smaller file sizes.

There is also asimilarly named libraryfrom theISO,which aims to be a complete implementation of JPEG,JPEG XTandJPEG-LSstandards.

libjpeg-turbo

libjpeg-turbo

Developer(s)	libjpeg-turbo Project
Initial release	November 19, 2010(2010-11-19)
Stable release	3.0.4 / 14 September 2024(14 September 2024)
Repository	github.com/libjpeg-turbo
Website	libjpeg-turbo.org

libjpeg-turbo is aforkof libjpeg that usesSIMDinstructionsto accelerate baseline JPEG encoding and decoding. Many projects are now using libjpeg-turbo instead of libjpeg, including popular Linux distributions (Fedora,Debian,Mageia,openSUSE,...),Mozilla,andChrome.Apart from performance, some projects have chosen to use libjpeg-turbo because it allows them to retain backwardABIcompatibility with the older libjpeg v6b release.libjpeg v7, v8 and v9 broke ABI compatibility with prior releases.

libjpeg-turbo implements the standard-compliant arithmetic coding and lossless crop features seen in libjpeg v7. It can also be configured to be compatible with the libjpeg v7 or v8 ABI, but it does implement DCT scaling and the proprietary SmartScale, which builds on DCT scaling.libjpeg-turbo chooses not to support SmartScale, because it is not anITU-Tstandard and because their own research finds it (and DCT scaling) ineffective.By extension, since the only major new feature in libjpeg v9 is specific to the SmartScale format, the libjpeg-turbo Project has chosen to forgo emulating libjpeg v9.

Since 2019, libjpeg-turbo is one of the two JPEG reference implementations, available as ISO/IEC 10918-7 and ITU-T T.873.The other reference implementation is ISO libjpeg which also includes support for JPEG XT and JPEG LS.

MozJPEG

MozJPEG

MozJPEG tries several partitionings of the spectrum of DCT coefficients
Developer(s)	Mozilla Research
Initial release	March 4, 2014(2014-03-04)
Stable release	4.1.5 / October 12, 2023(2023-10-12)
Website	github.com/mozilla/mozjpeg

MozJPEG is a fork from libjpeg-turbo done by Josh Aas and others from Mozilla Research. It aims to speed up loading times of webpages by achieving a reduction in file size (of about 10%) and therefore transmission time through improvement of coding efficiency while retaining image quality. To achieve this, it uses more processing power for the encoding (asymmetry) while retaining full compatibility with the JPEG standard and requiring no changes on the decoder side.

The techniques MozJPEG uses to achieve high compression include optimisingHuffmantrees, using progressive coding to optimally split the spectrum of DCT coefficients into separate scans, and through the use oftrellis quantisation.Additionally, the presets are aggressively tuned towards the minimisation of file sizes.

Besides libjpeg-turbo, MozJPEG also builds upon jpegcrush, aPerlscript by Loren Merritt.

Jpegli

Jpegli

Developer(s)	Google
Initial release	November 14, 2020(2020-11-14)
Stable release	0.10.2 / March 8, 2024(2024-03-08)
Website	github.com/google/jpegli

In April 2024, Google introducedJpegli,a new JPEG coding library that offers enhanced capabilities and a 35% compression ratio improvement at high quality compression settings, while the coding speed is comparable with MozJPEG.

ISO libjpeg

Main article:JPEG XT § libjpeg

ISO/IECJoint Photography Experts Groupmaintains a reference software implementation for baseJPEG(ISO/IEC 10918-1 and 18477-1) andJPEG XTextensions (ISO/IEC 18477 Parts 2 and 6-9), as well as losslessJPEG-LS(ISO/IEC 14495).It also includes some of the optimizations of MozJPEG. Though also named libjpeg, it is not related to the source code provided by Independent JPEG Group (IJG) and does not support proprietary extensions introduced by IJG since 2007.

See also

• Lossless editing
• The Guetzli JPEG encoder

External links

• JPEG FAQs
• Nyman, Robert; Aas, Josh (Aug 6, 2014)."Using MozJPEG to Create Efficient JPEGs".Hacks.Mozilla.