Here I try to find out if it is really worth to convert images to webp instead of serve them as minified jpeg.
To minify jpeg I use mozjpeg lossy compression first and jpegtran lossless compression after. For 70% of images jpegtran do nothing, but for the rest it helps to save 10-40% more Looks like mozjpeg works fine without jpegtran since 3.2 version.
It compares saved size and loss in quality by SSIM
clone repo, then run:
npm i
npm start
You can put your own images into ./src
I suggest you empirically find out quality settings for imagemin-webp and imagemin-mozjpeg which will return equal SSIM for compressed images. And then check what compression method will save more bytes.
For imageset from this repo quality settings to have equal SSIM will be: webp - 80, mozjpeg - 84. And webp will win with 28% more savings.
For different imagesets which I have tested with imagemin settings which returns equal SSIM, webp always win with savings varying from 20% to 30%.