libjpeg

From Wikipedia, the free encyclopedia
  (Redirected from Jpegtran)
Jump to: navigation, search
libjpeg
Logo JPEG 9
Cjpeg-screenshot.png
Developer(s) Independent JPEG Group
Initial release October 7, 1991; 22 years ago (1991-10-07)
Stable release 9a / January 19, 2014; 5 months ago (2014-01-19)
Development status active
Written in C
Operating system Cross-platform
Type library
License Custom free software license; can be used in any application without royalty, with acknowledgment.
Website ijg.org

libjpeg is a widely used free software library written in C which implements JPEG decoding and encoding functions alongside various utilities for handling JPEG images. This library is maintained by the Independent JPEG Group (IJG), an informal organization which is not affiliated with the JPEG ISO committee.

The Open Source software implementation of the Independent JPEG Group (IJG), as well as being one of the major Open Source packages, was key to the success of the JPEG standard and was incorporated by many companies into a variety of products such as image editors and Internet browsers.[1]

The widely used IJG implementation was first publicly released in October 1991 and has been considerably developed since that time. 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.[2]

Utilities[edit]

The following utility programs are available 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 – a utility for lossless transcoding between different JPEG formats.

The jpegtran command-line program is useful to:

  • optimize the Huffman coding layer of a JPEG file to increase compression,
  • convert to JPEG Arithmetic coding to further increase compression (and back),[3][4][5]
  • convert between progressive and non-progressive JPEG formats,
  • eliminate non-standard application-specific data inserted by some image programs, or
  • to perform certain transformations on a file, such as:

...all done "losslessly" (i.e. without decompressing and recompressing the data, and so causing a reduction of image quality due to generation loss).

There is an associated Windows application, Jpegcrop, which provides a user interface to jpegtran. More programs supporting JPEG lossless transformation functions based on the IJG code are given on the Lossless Applications List.

Version roadmap[edit]

Overview[edit]

There are currently two conditions which trigger a major version bump of the JPEG library:

  1. New types of files can be created which are not compatible with prior releases, and
  2. Changes in the master records which break the binary compatibility (usually addition of entries for new functions).

In all major upgrades since v6 both conditions 1. and 2. came together, while the source compatibility (API) could largely be retained.

Major version New file format feature New master record entries References
Old version, no longer supported: 6 progressive JPEG support progressive_mode ... ITU-T Recommendation T.81
ISO/IEC IS 10918-1
Old version, no longer supported: 7 arithmetic coding support scale_num/scale_denom for
compression (encoding) ...
ITU-T JPEG-Plus Proposal ...[7]
Old version, no longer supported: 8 SmartScale
(variable block size)
block_size/lim_Se etc. Evolution of JPEG[8]
Current stable version: 9 internal color transform
(FF F8 LSE extension marker)
color_transform JPEG 9 Lossless Coding[9]
InfAI JPEG Development Site[10]
Legend: Old version Older version, still supported Current version Latest preview version Future release

For version 7 both conditions were different subjects (arith_code entry already existed), other versions are same subject.

Timeline[edit]

libjpeg-turbo[edit]

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 Fedora (since Fedora 14), Mozilla (since Firefox 5.0, while Firefox 13.0 and later gain additional performance by adding the accelerated Huffman coding routines from libjpeg-turbo 1.2.0 and later, which were previously excluded due to a license conflict), and Google Chrome (since version 11).[11][12][13] 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.[14] libjpeg v7, v8 and v9 broke ABI compatibility with prior releases.[15]

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.[16] 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.[17] Therefore, SmartScale files created by libjpeg v8 and later will not be decompressed correctly by libjpeg-turbo.

See also[edit]

References[edit]

External links[edit]