Libjpeg

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libjpeg is a library written entirely in C which contains a widely-used implementation of a JPEG decoder, JPEG encoder and other JPEG utilities. This library is maintained by the Independent JPEG Group.

Utilities

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 JFIF 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 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:
  • grayscaling,
  • rotating and flipping (within certain limits), and
  • cropping

...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.

libjpeg-turbo

libjpeg-turbo is a fork of libjpeg that uses SIMD instructions to accelerate JPEG encoding and decoding. Fedora 14 switched to libjpeg-turbo in 2010. Mozilla switched to libjpeg-turbo in Firefox 5.0.^[1]Chrome 11 also has switched to this version.^[2] The switch to turbo-jpeg was accelerated by the fact that libjpeg broke compatability with earlier versions at release 7, putting many basic applications in the awkward position of requiring upgrades to the entire software base of a user's computer. Libjpeg-turbo doesn't suffer from this incompatibility, hence it was easier to change libraries rather than deal with the Independent JPEG Group's arrogance.

See also

• JPEG
• Lossless editing

References

External links

• Independent JPEG Group Website
• Binary package of libjpeg for Microsoft Windows (at GnuWin32 in SourceForge)
• Binary packages of libjpeg for Microsoft Windows (MingW and Microsoft Visual C++ versions 7 and 8), and for Mac OS X (Universal, GCC 4.0; PowerPC, GCC 4.0; PowerPC, GCC 3.3) (at ClanLib)
• libjpeg-turbo, an ABI-/API-compatible extension of libjpeg which uses x86 SIMD instructions to achieve a substantial speedup over the reference implementation.
• Jpeg Faqs
• Additional features for libjpeg