Can Google’s Guetzli Slash Your Web Image Size Without Visible Quality Loss?
The article reviews Google’s Guetzli JPEG compressor, shares real‑world testing on a large high‑resolution image, discusses memory and CPU requirements, shows size reductions across quality settings, and offers practical advice for integrating it into web projects.
Community guide: This article introduces Google’s image compression software Guetzli and highlights usage considerations.
Google to the rescue
Google recently released a new JPEG compression algorithm called Guetzli. Its main idea is to preserve details that the human eye can easily recognize while discarding those that are not noticeable, aiming for the same perceived quality with smaller file sizes.
It is not a new image format but a new way to compress JPEGs, so any software that can render JPEG can display the results.
Guetzli in real life
In a project with a homepage containing about 30 MB of assets (27 MB of which are images), I tried Guetzli on an unused high‑resolution JPEG (8574×5715, 22 MB). The first attempt crashed because Guetzli requires roughly 300 MB of RAM per megapixel, which meant the 22 MB image needed about 15 GB of memory.
After freeing some memory, the second run succeeded using 12 GB of RAM and took a little over 40 minutes (Google states about one minute per megapixel).
The compressed image was under 7 MB, a reduction from 22 MB, and the visual difference was “so small it’s almost unbelievable.”
6.9M home-guetzli.jpg 22M home-raw.jpg
Using Guetzli’s default quality range (84–100), I experimented with different quality factors via a simple script that could run unattended.
Results (default quality factor appears to be 95):
6.9M ./home-guetzli.jpg 22M ./home-raw.jpg 3.0M ./home-raw.jpg.guetzli84.jpg 3.4M ./home-raw.jpg.guetzli87.jpg 4.2M ./home-raw.jpg.guetzli90.jpg 5.5M ./home-raw.jpg.guetzli93.jpg 8.8M ./home-raw.jpg.guetzli96.jpg 18M ./home-raw.jpg.guetzli99.jpg
The product owner and designer agreed on using a quality factor of 84. After converting all images, the homepage size dropped from 30 MB to under 8 MB (about 3 MB of that is CSS and scripts). The original images had not been compressed before.
Additional notes
Installing Guetzli on my machine was straightforward (an AUR package exists for Arch Linux, and a Homebrew formula is available for macOS). It runs as a single‑core process and requires sufficient RAM; parallel instances are possible if memory permits.
Guetzli cannot output PNGs (no transparency) but can compress PNGs by converting them to JPEG.
Compression efficiency depends on the source image quality: large images saw up to a 7× size reduction, while small images saw about a 2× reduction, with more noticeable quality loss on the latter.
In a few cases I observed slight color saturation loss, which was acceptable for my use case.
Long story short
Give Guetzli a try; it may produce unacceptable results at low quality settings, but it can also shave several megabytes off your website’s image payload.
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