Google Touts Smaller JPEGs With Open Source Guetzli Encoder

The company bills this as a new (albeit slow at the moment) way for websites to crunch their images, reducing file size for faster page loading without sacrificing quality.

"Butteraugli takes into account. properties of vision that most JPEG encoders do not make use of", Google researchers said in a Guetzli research paper (PDF). This will enable webmasters to develop webpages that can load faster while using comparatively less data.

In fact, Google claims that its research shows that even when image file sizes are the same (meaning the libjpeg files are encoded in a higher quality setting, resulting in larger file sizes), human raters like the Guetzli images better. The name Guetzli means cookie in Swiss German. The website notes that one big distinction is that unlike some other image compression techniques like WebP and WebM, these new JPEGs are compatible with the current JPEG standard and also current devices, browsers and photo editing apps. Guetzli strikes a balance between minimal loss and file size by employing a search algorithm that tries to overcome the difference between the psychovisual modeling of JPEG's format, and Guetzli's psychovisual model, which approximates color perception and visual masking in a more thorough and detailed way than what is achievable by simpler color transforms and the discrete cosine transform.

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Secondly, Guetzli would seem set to have a significant resource footprint compared to the long-established image compression libraries now in use (mostly over Apache or other Linux-based frameworks). Uncompressed original is on the left.

Google is offering the Guetzli encoder as an open source software project for anyone to check out and possibly improve. Presumably Google are considering optimisations and rational solutions to speed up Guetzli's compression speed performance. For example, a multi-megabyte image stored in BMP or PNG format can look nearly exactly the same converted to a JPEG that's only a few hundred kilobytes in size.

Although Guetzli primarily aims at compressing the file size, Google also points out that it can also be used to increase the quality of the image without compromising on the size. Last, we hope that the new explicitly psychovisual approach in Guetzli will inspire further image and video compression research.

  • Delia Davidson