Google Touts Smaller JPEGs With Open Source Guetzli Encoder
"That's why we're excited to announce Guetzli, a new open source algorithm that creates high quality JPEG images with file sizes 35% smaller than now available methods, enabling webmasters to create webpages that can load faster and use even less data". "However, while Guetzli creates smaller image file sizes, the tradeoff is that these search algorithms take significantly longer to create compressed images than now available methods". In fact, in experiments comparing compressed images, human raters preferred the Guetzli-produced images over those created by libjpeg, even when the latter's images were a larger file size.
Although there are several different ways to adjust the size and quality of a JPEG, Google's Guetzli (German for "cookie") is all about the "quantization stage of compression". If Guetzli does work as well as Google claims, this could potentially be a solid libjpeg replacement for web developers, designers, or photographers. The uncompressed image is on the left, the libjpeg version is in the middle, and the Guetzli version is on the right.
This potentially would allow webmasters for example to create much more compact websites that take less time (and data) to load - a potential boon to smartphone users surfing the web on mobile devices. Ultimately, that means these smaller images will look just as good to the average person.
Guetzli is the product of Google Research Europe, and has been released under the Apache open source license. 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. Alternatively, it's now possible to significantly improve the image quality of a file without raising its size. Each can be optimized, and Guetzli focuses specifically on the quantization stage as this is typically where visual quality is lost. Google's tests showed that Guetzli outdoes Mozilla's tool by 29 to 45 percent.
For more details on the nitty-gritty of how Guetzli actually accomplishes the improved encoding (it apparently involves "psychovisual models") check out the Google Research Blog and the published paper on Guetzli.