Mozilla's new Mozjpeg 2.0 image encoder improves JPEG compression

By on July 16, 2014, 1:45 PM
mozilla, software, compression, jpeg

Mozilla yesterday announced the launch of an updated version of its JPEG compression tool Mozjpeg. The latest version (2.0) snips down file sizes by 5 percent on average compared to the widely used libjpeg-turbo.

Although that might look like a small number, it's significant for image-heavy sites like Facebook, helping them save bandwidth and render faster. Also, depending on the image, that number can vary from slightly less than 5 percent to as high as 15 percent.

"The end goal is to reduce page load times and ultimately create an enhanced user experience for sites hosting images", said Josh Aas, senior technology strategist for Mozilla.

He also added that unlike Mozjpeg 1.0, which only focused on progressive JPEGs, the new version also improves images saved in the baseline format.

The project is being backed by Facebook, which has already begun testing the tool. The social network has also donated $60,000 to Mozilla to continue its work on this technology, including the next iteration, Mozjpeg 3.0.

"Facebook supports the work Mozilla has done in building a JPEG encoder that can create smaller JPEGs without compromising the visual quality of photos", Facebook software engineer Stacy Kerkela said. "We look forward to seeing the potential benefits mozjpeg 2.0 might bring in optimizing images".

The libjpeg-turbo library, on which Mozjpeg is based, uses fewer CPU cycles than the Mozilla's tool, and powers JPEG decoding in Firefox. "We recommend using libjpeg-turbo for a standard JPEG library and any decoding tasks. Use mozjpeg when creating JPEGs for the Web", Aas wrote.

The JPEG format, which has been in use for more than 20 years, is one of the most widely used image formats on the Internet. It's a lossy format, which means that you can remove some data to reduce the file size without significantly affecting the original image’s integrity.

Google has been promoting the use of its WebP image format, a derivative of the video format VP8, but Mozilla has long resisted the call to adopt it. A Mozilla study from 2013 concluded that newer formats such as WebP or JPEG XR were not significantly better than JPEG.

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