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from the just-use-a-photocopier-multiple-times dept.
Google has developed and open-sourced a new JPEG algorithm that reduces file size by about 35 percent—or alternatively, image quality can be significantly improved while keeping file size constant. Importantly, and unlike some of its other efforts in image compression (WebP, WebM), Google's new JPEGs are completely compatible with existing browsers, devices, photo editing apps, and the JPEG standard.
The new JPEG encoder is called Guetzli, which is Swiss German for cookie (the project was led by Google Research's Zurich office). Don't pay too much attention to the name: after extensive analysis, I can't find anything in the Github repository related to cookies or indeed any other baked good.
There are numerous ways of tweaking JPEG image quality and file size, but Guetzli focuses on the quantization stage of compression. Put simply, quantization is a process that tries to reduce a large amount of disordered data, which is hard to compress, into ordered data, which is very easy to compress. In JPEG encoding, this process usually reduces gentle colour gradients to single blocks of colour and often obliterates small details entirely.
The difficult bit is finding a balance between removing detail, and keeping file size down. Every lossy encoder (libjpeg, x264, lame) does it differently.
(Score: 2) by KritonK on Monday March 20 2017, @09:40AM
I just tried it. While I usually create JPEGs with a quality of 75 (the default for cjpeg) for my web pages, guetzli will refuse to create JPEGs with a quality of less than 84, unless you tweak the source, claiming that using a lower quality will introduce artifacts.
Thus, while guetzli does produce smaller files than cjpeg with a quality of 84, both of these files are larger than the file produced by cjpeg wth a quality of 75.
The quality is supposed to be better, but, quite frankly, I couldn't tell the difference among any of the above three files or the original, and this was with the sample supplied by google, which one would assume that it would have been chosen to show off guetzli's abilities.