libjpeg

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libjpeg
Logo IJG libjpeg v9
Developer(s) Independent JPEG Group
Initial release October 7, 1991; 26 years ago (1991-10-07)
Stable release
9c / January 14, 2018; 8 months ago (2018-01-14)
Written in C
Operating system Cross-platform
Type library
License Custom BSD-like (free software)
Website ijg.org

libjpeg is a free library with functions for handling the JPEG image data format. It implements a JPEG codec (encoding and decoding) alongside various utilities for handling JPEG data. It is written in C and distributed as free software together with its source code under the terms of a custom permissive (BSD-like) free software license, which demands attribution. The original variant is maintained and published by the Independent JPEG Group (IJG). Meanwhile, there are several forks with additional features.

JPEG JFIF images 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.[1]

Utilities[edit]

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[edit]

jpegtran transforms JPEG data without reencoding
(here with user interface CropGUI)

The command-line program jpegtran provides several features for reformatting and recoding the representation of the DCT coefficients, for transformation of actual image data and for discarding auxiliary data in JPEG files, respectively. The transformations regarding the representation of the coefficients comprise:

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 and flipping in steps of 90 degrees,
    • cropping at image block borders (every 8×8 or 16×16 pixels),
    • rescaling.[5]

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

There is an associated Windows application, Jpegcrop, which provides a user interface to jpegtran. For Unix-like systems like Linux there is the free CropGUI with similar functionality. More programs supporting JPEG lossless transformation functions based on the IJG code are given on the Lossless Applications List.

History[edit]

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 by Tom Lane. The open-source implementation 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.[6]

For version 5, which was released on September 24, 1994, the whole code base was rewritten. It introduced the utility programs rdjpgcom and wrjpgcom for 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 program jpegtran. This utility was extended with features to rotate and flip images and grayscale reduction in version 6b.

From version 6b of libjpeg of 27 March 1998, Miyasaka Masaru forked a branch named libjpeg/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.[7]

After 11 years and a change in leadership, the IJG released new versions of libjpeg (7 through 9), of which each broke ABI compatibility with previous versions.[8] The changes that were held in prospect after the 6x series were not delivered.[9] In version 7, support for arithmetic coding was introduced, which earlier has been rejected because of the patent situation, as well as the crop feature in jpegtran (-crop).[9]

Versions 8 and 9 served basically for the introduction of controversial[10] incompatible format extensions. These are widely regarded as ineffective and inferior to existing, standardised solutions.[11][12] Their standardisation was rejected after submission to the ITU-T. The original organiser Tom Lane and others criticize these changes as a break from the goals of the IJG.[10]

On 4 March 2014, the first version of the filesize-optimising fork mozjpeg was published. For this version Josh Aas from Mozilla Research reworked the Perl script jpegcrush from x264's main developer Loren Merritt and integrated it into the code base of libjpeg-turbo.[13]

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. donated 60000 dollars for the development of the next version,[14] and CloudFlare assigned a developer for the improvement of mozjpeg.[15]

Versions[edit]

Version Released New features
ITU T.81 JPEG Compatible
Old version, no longer supported: 1 1991 First release
Baseline or optimized JPEG
GIF or PPM output
Old version, no longer supported: 2 1991 Internal improvements
More input/output formats
Old version, no longer supported: 3 1992 Internal and image quality improvements
Old version, no longer supported: 4 1992 Internal and speed improvements
Old version, no longer supported: 4a 1993-02-18
Old version, no longer supported: 5 1994-09-24 Internal improvements and revised API
Old version, no longer supported: 5a 1994-12-07
Old version, no longer supported: 5b 1995-03-15
Old version, no longer supported: 6 1995-08-02 Progressive JPEG
jpegtran (convert between baseline and progressive)
Old version, no longer supported: 6a 1996-02-07
Old version, no longer supported: 6b 1998-03-27 jpegtran extended to lossless rotate
Proprietary non-compatible extensions
Old version, no longer supported: 7 2009-06-27 jpegtran extended to lossless crop

T.851 Arithmetic Coding[16]
SmartScale extension[17][18]

Old version, no longer supported: 8 2010-01-10 Internal fixes
jpegtran extended to use SmartScale
Old version, no longer supported: 8a 2010-02-28 RGBA
Old version, no longer supported: 8b 2010-05-16
Old version, no longer supported: 8c 2011-01-16 Variable DCT block size
Old version, no longer supported: 8d 2012-01-15 RGB JPEG (no color transform to YCbCr)
Old version, no longer supported: 9 2013-01-13 YCoCg color
Lossless compression[19]
Old version, no longer supported: 9a 2014-01-19 Wide color gamut (JFIF v2)
8-12 bit color
Old version, no longer supported: 9b 2016-01-17
Current stable version: 9c 2018-01-14
Legend: Old version Older version, still supported Current stable version Latest preview version Future release

Forks[edit]

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

There is also a similarly named library from the ISO, which aims to be a complete implementation of JPEG, JPEG XT and JPEG-LS standards.[20]

libjpeg-turbo[edit]

libjpeg-turbo
Logo libjpeg-turbo
Developer(s) libjpeg-turbo Project
Initial release 2010; 8 years ago (2010)
Stable release
2.0.0 / July 27, 2018; 57 days ago (2018-07-27)
Website libjpeg-turbo.org

libjpeg-turbo is a fork of libjpeg that uses SIMD instructions to accelerate baseline JPEG encoding and decoding. Many projects are now using libjpeg-turbo instead of libjpeg, including popular GNU/Linux distributions (Fedora, Debian, Mageia, openSUSE, ...), Mozilla, and Chrome.[21][22][23] Apart from performance, some projects have chosen to use libjpeg-turbo because it allows them to retain backward ABI compatibility with the older libjpeg v6b release.[24] libjpeg v7, v8 and v9 broke ABI compatibility with prior releases.[8]

libjpeg-turbo can be configured to be compatible with the libjpeg v7 or v8 ABI, but it does not implement the complete set of features in recent IJG releases, including the SmartScale format extension.[25] The libjpeg-turbo Project has chosen not to support SmartScale, citing concerns regarding the fact that it is not an ITU-T standard and citing their own research that questions the usefulness of the feature. 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.[11] Therefore, SmartScale files created by libjpeg v8 and later will not be decompressed correctly by libjpeg-turbo.

mozjpeg[edit]

mozjpeg
mozjpeg
mozjpeg tries several partitionings of the spectrum of DCT coefficients
mozjpeg tries several partitionings of the spectrum of DCT coefficients
Developer(s) Mozilla Research
Initial release March 4, 2014; 4 years ago (2014-03-04)
Stable release
3.3.1 / March 17, 2018; 6 months ago (2018-03-17)[26]
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 at unchanged 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 optimising Huffman trees, using progressive coding to optimally split the spectrum of DCT coefficients into separate scans, and through the use of trellis quantisation. Additionally, the presets are aggressively tuned towards the minimisation of file sizes.

Besides libjpeg-turbo, mozjpeg also builds upon jpegcrush, a Perl script by Loren Merritt.[13][27]

ISO libjpeg[edit]

libjpeg
Developer(s) Thomas Richter /JPEG Reference AhG
Initial release July 27, 2012; 6 years ago (2012-07-27)
Stable release
1.53 / May 18, 2017; 15 months ago (2017-05-18)
Website github.com/thorfdbg/libjpeg

ISO/IEC Joint Photography Experts Group maintains a reference software implementation for base JPEG (ISO/IEC 10918-1 and 18477-1) and JPEG XT extensions (ISO/IEC 18477 Parts 2 and 6-9), as well as lossless JPEG-LS (ISO/IEC 14495).[28]. 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[edit]

References[edit]

  1. ^ JPEG JFIF
  2. ^ Jpegcrop Preferences and Options description
  3. ^ Filmic Games >> The greatest failure of our patent system was... Archived 2012-09-01 at the Wayback Machine.
  4. ^ 680385 - Firefox does not show arithmetic coded jpegs
  5. ^ New jpegtran features
  6. ^ JPEG homepage
  7. ^ http://libjpeg-turbo.virtualgl.org/
  8. ^ a b "libjpeg: API/ABI changes review". Retrieved 2017-10-28. 
  9. ^ a b Mans Rullgard (Hardwarebug.org), August 4, 2009: IJG is back
  10. ^ a b Tom Lane, January 16, 2013: jpeg-9, API/ABI compatibility, and the future role of this project
  11. ^ a b "What About libjpeg v9?". libjpeg-turbo team. Retrieved February 8, 2013. 
  12. ^ Mans Rullgard (Hardwarebug.org), February 1, 2010: IJG swings again, and misses
  13. ^ a b André Kramer (heise.de-Newsticker), January 14, 2013: Mozilla-Encoder verbessert JPEG-Kompression
  14. ^ Sebastian Grüner, 16. Juli 2014: mozjpeg 2.0: Facebook unterstützt JPEG-Encoder von Mozilla
  15. ^ http://www.soeren-hentzschel.at/mozilla/2014/07/30/cloudflare-moechte-zu-mozillas-jpeg-encoder-beitragen/
  16. ^ "ITU-T T.81 (JPEG-1)-based still-image coding using an alternative arithmetic coder" (pdf). September 2009. 
  17. ^ ITU-T JPEG-Plus Proposal R3
  18. ^ Evolution of JPEG
  19. ^ JPEG 9 Lossless Coding
  20. ^ https://github.com/thorfdbg/libjpeg
  21. ^ Software That Uses or Provides libjpeg-turbo. February 9, 2012.
  22. ^ Issue 48789 – chromium – Use libjpeg-turbo instead of libjpeg. April 14, 2011.
  23. ^ Bug 698519 – Update to libjpeg-turbo 1.2. February 28, 2012
  24. ^ libjpeg for F14. February 9, 2012.
  25. ^ libjpeg-turbo README file Archived 2014-08-12 at the Wayback Machine.
  26. ^ "mozilla/mozjpeg". GitHub. March 17, 2018. Retrieved September 17, 2018. 
  27. ^ Andreas Donath (golem.de), March 6, 2014: Mozilla will JPEGs besser komprimieren
  28. ^ https://jpeg.org/jpegxt/software.html

External links[edit]