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.

Similar functionality is provided in the JPG_TRANSFORM plugin to IrfanView.

See also

• JPEG
• Lossless editing

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)
• Jpeg Faqs
• Additional features for libjpeg