Google's new algorithm can compress JPEGs 35% more than now available methods

Janie Parker
March 18, 2017

If you're building an app or site that stores, manipulates or serves a lot of images, you'll want to consider implementing Google's new image compression algorithm, which promises to reduce JPEG file sizes by 35 percent more than other methods. According to the Google blog announcement post, "Guetzli is a JPEG encoder for digital images and web graphics that can enable faster online experiences by producing smaller JPEG files while still maintaining compatibility with existing browsers, image processing applications and the JPEG standard". In addition to making image files that are smaller, Guetzli is also focused on creating images that look better than other compressed images, too.

"This is similar to our Zopfli algorithm, which produces smaller PNG and gzip files without needing to introduce a new format", said Google.

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The project is an image encoder called Guetzli (which is Swiss German for cookie; the project was born out of Google Research's Zurich office). To accomplish this, Guetzli trades visual quality for a smaller file size at the quantization stage of image compression. Comparing it to one of the popular JPEG encoders - libjpeg, Google Research says that "75 percent of ratings are in favour of Guetzli".

JPEG compression has several steps, including color space transformation, discrete cosine transformation, and quantization. Other methods mostly get the job done by leaving out minor details, while Guetzli compresses the image without compromising on the quality. This basically means that the process is based on the way humans see objects, so the encoder uses the way people see to decide which areas of the JPEG can be reduced, thus compressing it in such a way that the quality is improved. If that's not something you care about, you can head over to the Github destination instead and check out all the files, instructions on installing the tool, and the code necessary for using it. Right: Guetzli. Google claims that Guetzli has fewer artifacts without a larger file size. The second image is encoded with libjpeg and the third image uses Guetzli. "Although Guetzli may be too slow for many practical uses, we hope that it can show direction for future image format design", the researchers said.

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