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Mozilla Releases Mozjpeg 2.0 Share This on LinkedIn   Share This on Google   Tweet This   Forward This

15 July 2014

Mozilla Research has released mozjpeg.20, according to a blog post by Josh Aas earlier today. Mozjpeg is "a production-quality JPEG encoder that improves compression while maintaining compatibility with the vast majority of deployed decoders," Aas said.

With the adoption of trellis quantization in the new release, Aas reports a five percent reduction in file size for both baseline and progressive JPEGs compared to standard JPEG performance. Previously file sizes were reduced only for progressive JPEGs:

With today's release, mozjpeg 2.0 can reduce file sizes for both baseline and progressive JPEGs by five percent on average compared to those produced by libjpeg-turbo, the standard JPEG library upon which mozjpeg is based. Many images will see further reductions.

In a footnote, he put the encoding/decoding issue in perspective:

We're fans of libjpeg-turbo -- it powers JPEG decoding in Firefox because its focus is on being fast and that isn't going to change any time soon. The mozjpeg project focuses solely on encoding and we trade some CPU cycles for smaller file sizes. We recommend using libjpeg-turbo for a standard JPEG library and any decoding tasks. Use mozjpeg when creating JPEGs for the Web.

Enhancements to the initial release in March include:

  • Trellis quantization to reduce file sizes for both baseline and progressive images
  • The cjpeg utility now supports JPEG input in order to simplify re-compression workflows
  • New options to specifically tune for PSNR, PSNR-HVS-M, SSIM, and MS-SSIM metrics
  • Generates a single DC scan by default to be compatible with decoders that can't handle arbitrary DC scans

Aas reported that Facebook has made a $60,000 contribution to mozjpeg development and is testing the technology on

And Mozilla Research has set up a thread on Google Groups to encourage discussion of the new technology.

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