Guetzli – A New JPEG encoder by Google


Last week, Google released a open source JPEG encoder that can create images file sizes 35% smaller than currently available methods, enabling webmasters to create webpages that can load faster and use even less data. Using a different method than other optimizers, Guetzli doesn’t have a set of rules or laws in a race to the lowest file size when encoding images.

Guetzli is a JPEG encoder that aims for excellent compression density at high visual quality and can enable faster online experiences by producing smaller JPEG files while still maintaining compatibility with existing browsers, image processing applications and the JPEG standard.

The visual quality of JPEG images is directly correlated to its multi-stage compression process: color space transform, discrete cosine transform, and quantization. Guetzli specifically targets the quantization stage in which the more visual quality loss is introduced, the smaller the resulting file.

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.

However, while Guetzli creates smaller image file sizes, the tradeoff is that these search algorithms take significantly longer to create compressed images than currently available methods.