libjpeg is a free library that contains C software to implement JPEG image encoding, decoding, and transcoding.
This package 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. The original variant is maintained and published by the Independent JPEG Group (IJG).
Provision is made for supporting all variants of these processes, although some uncommon parameter settings aren't implemented yet. There has been no provision for supporting the hierarchical or lossless processes defined in the standard.
A set of library routines is provided for reading and writing JPEG image files, plus two sample applications "cjpeg" and "djpeg", which use the library to perform conversion between JPEG and some other popular image file formats. The library is intended to be reused in other applications.
In order to support file conversion and viewing software, there is considerable functionality beyond the bare JPEG coding/decoding capability; for example, the color quantization modules are not strictly part of JPEG decoding, but they are essential for output to colormapped file formats or colormapped displays. These extra functions can be compiled out of the library if not required for a particular application.
There is also "jpegtran", a utility for lossless transcoding between different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple applications for inserting and extracting textual comments in JFIF files.
9 July 2021
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