Libjpeg
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| Developer(s) | Independent JPEG Group |
|---|---|
| Initial release | October 7, 1991 |
| Stable release |
9b / January 17, 2016
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| Development status | active |
| Written in | C |
| Operating system | Cross-platform |
| Type | library |
| License | Custom BSD-like (free software) |
| Website | ijg |
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| Developer(s) | libjpeg-turbo Project |
|---|---|
| Initial release | 2010 |
| Stable release |
1.5.1 / September 21, 2016
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| Development status | active |
| Website | libjpeg-turbo.org |
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mozjpeg tries several partitionings of the spectrum of DCT coefficients
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| Developer(s) | Mozilla Research |
|---|---|
| Initial release | March 4, 2014 |
| Stable release |
3.1 / May 18, 2015
|
| Development status | active |
| Website | github.com/mozilla/mozjpeg |
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.
The following utility programs are shipped together with libjpeg:
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:
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.
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