Google's Guetzli Open Source JPEG Encoder Compresses Images by 35 Percent

Mar 18, 2017, 00:58
Google's Guetzli Open Source JPEG Encoder Compresses Images by 35 Percent

This is not the first time when Google has done something new regarding image compression, however, among all of its other algorithms, this one is compatible with most of the browser, apps, and JPEG standards.

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).

The prize may be worth the effort: JPEG, long since the victor the image format wars of the late 1990s, now joins PNG in accounting for 73% of all content in websites - petabytes of data on a rolling basis, largely using technologies and standards which have not changed in almost twenty years.

Google has cautioned that while its algorithm manages to significantly compress JPEG files with minimal loss in visual quality, the drawback is that the compression process requires considerably more time than current methods. Also, it is worth noting that Guetzli takes more time for image compression in comparison to libjpeg.

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Google has several other projects to reduce image sizes on the web, including its Zopfli encoder (which similarly creates smaller PNG files without breaking format compatibility) and WebP (a new image format that supports both lossless and lossy compression for improved file sizes). "We think this makes the slower compression a worthy tradeoff". "This implies the Butteraugli psychovisual image similarity metric which guides Guetzli is reasonably close to human perception at high-quality levels".

Google said its new algorithm will create "high quality JPEG images with file sizes 35 percent smaller than now available methods". Guetzli fiddles with two particular parts of JPEG compression - discrete cosine transform, which governs how details like object edges are recorded, and quantization, which governs which colors are preserved and which are sacrificed to cut file size. It would be interesting to see if Guetzli scores a wider acceptance.

Guetzli is the product of Google Research Europe, and has been released under the Apache open source license. Google's tests showed that Guetzli outdoes Mozilla's tool by 29 to 45 percent.

Furthermore, Google claims that Guetzli does this compression without compromising on image quality. And although Google compared Guetzli to mozjpeg and another JPEG encoder called libjpeg, there are other options, too. "Guetzli is rather slow to encode", the researchers said, suggesting it's most likely useful on image-heavy websites.