Google Releases Guetzli Open Source JPEG Encoder Generating 20 to 35% Smaller Files Compared to Libjpeg

Google has been working one several front to make data and images smaller, hence faster to load from the Internet, with project such as Zopfli algorithm producing smalled PNG & gzip files, or WebP image compression algorithm that provides better lossless compression compare to PNG, and better lossy compression compared to JPEG, but requires updated support from clients such as web browsers. Google has now released Guetzli algorithm that improve on the latter, as it can create JPEG files that are 20 to 35% smaller compared to libjpeg with similar quality, and still compatible with the JPEG format.

The image above shows a close up on a phone line with the original picture, the JPEG picture compressed with libjpeg with the artifacts around the line, and a smaller JPEG picture compressed with Guetzli with less artifacts.

You can find out more about the algorithm in the paper entitled “Guetzli: Perceptually Guided JPEG Encoder“, or read the abstract below:

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.

The compression is quite slower than with libjpeg or libjpeg-turbo, but considering that on the Internet a file is usually compressed once, and decompressed many times by visitors, this does not matter so much. Another limitation is that it does not support progressive JPEG encoding.

You can try Guetzli by yourserlf as the code was released on github. It did the following to build the tool on Ubuntu 16.04:

You’ll the executable in bin/release directory, and you can run it to list all options:

Ideally you should have a raw or losslesly compressed image, but I tried a photo taken from my camera first:

But it reported my JPEG file was invalid, so I tried another file (1920×1080 PNG file):

It’s a single threaded process, and it takes an awful lot of time (about 3 minutes on an AMD FX8350 processor), at least with the current implementation. You may want to run it with “verbose” option to make sure it’s not dead.

I repeated the test with convert using quality 95, as it is the default option in Guetzli:

The file compressed with Guetzli is indeed about 15% smaller, and should have similar quality:

It’s just currently about 1,400 times slower on my machine.

Jean-Luc Aufranc (CNXSoft)

Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.

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