page_title: Libjpeg
section_title: mozjpeg
hierarchical_section_title: Libjpeg / Forks / mozjpeg
caption_attribution_description: English: Screenshot of the command line utility cjpeg from the libjpeg package in a preliminary release of version 2 from the mozjpeg project. Shown is verbose console output from the compression of a portable pixmap (PPM) file. Deutsch: Bildschirmphoto des Kommandozeilen-Werkzeuges cjpeg, einem Hilfsprogramm zu libjpeg, hier in eine Vorabausgabe von Version 2 der Variante vom mozjpeg-Projekt. Es zeigt ausführliche Konsolenausgabe von der Kompression einer Portable-Pixmap-Datei.
context_page_description: libjpeg is a free library with functions for handling the JPEG image data format. It implements a JPEG codec 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 free software license, which demands attribution.
  The original variant is maintained and published by the Independent JPEG Group. 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.
context_section_description: mozjpeg is a fork from libjpeg-turbo done by Josh Aas and others from Mozilla Research. It aims to speed up loading times of webpages by achieving a reduction in file size (of about 10%) and therefore transmission time through improvement of coding efficiency while retaining image quality. To achieve this, it uses more processing power for the encoding (asymmetry) while retaining full compatibility with the JPEG standard and requiring no changes on the decoder side.
  The techniques mozjpeg uses to achieve high compression include optimising Huffman trees, using progressive coding to optimally split the spectrum of DCT coefficients into separate scans, and through the use of trellis quantisation. Additionally, the presets are aggressively tuned towards the minimisation of file sizes.
  Besides libjpeg-turbo, mozjpeg also builds upon jpegcrush, a Perl script by Loren Merritt.
caption: mozjpeg tries several partitionings of the spectrum of DCT coefficients
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