Guetzli is Google's new free/open JPEG compression algorithm, which produces images that are more than a third smaller in terms of byte-size, and the resulting images are consistently rated as more attractive than traditionally compressed JPEGs. It's something of a web holy grail: much smaller, better-looking files without having to convince people to install a plugin or browser makers to support a new file-format.
Guetzli achieves new efficiencies in the quantization stage of JPEG compression, a major culprit for the loss of visual quality. Guetzli has its own psychovisualization model that improves on traditional JPEG models, discarding information more intelligently.
One downside: Guetzli is "extremely slow" relative to traditional compression, which might hinder the production of on-the-fly images. The authors don't quantify "extremely" slow, but note that it "may be too slow for many practical uses."
Guetzli is a new JPEG encoder that aims to produce visually indistinguishable images at a lower bit-rate than other common JPEG encoders. It optimizes both the JPEG global quantization tables and the DCT coefficient values in each JPEG block using a closed-loop optimizer. Guetzli uses Butteraugli, our perceptual distance metric, as the source of feedback in its optimization process. We reach a 29-45% reduction in data size for a given perceptual distance, according to Butteraugli, in comparison to other compressors we tried. Guetzli's computation is currently extremely slow, which limits its applicability to compressing static content and serving as a proof- of-concept that we can achieve significant reductions in size by combining advanced psychovisual models with lossy compression techniques.
Guetzli: Perceptually Guided JPEG Encoder [Jyrki Alakuijala, Robert Obryk, Ostap Stoliarchuk, Zoltan Szabadka, Lode Vandevenne and Jan Wassenberg/Computer Vision and Pattern Recognition]
Announcing Guetzli: A New Open Source JPEG Encoder
[Robert Obryk and Jyrki Alakuijala/Google Research]