Hi @Eckhard
I’ve recently found the same issue. I optimise my images before uploading, I uploaded a 15k png and a 2mb png came out! After doing some digging it looks like an issue with the Gregwar image library and not Grav directly - see https://github.com/Gregwar/Image/issues/115. Sadly the fix never got merged.
The only solution is to disable the Grav image caching as its not possible to just cache but not do image manipulations (which inflate the image size). While this loads the images directly (and hopefully faster) you miss out on the caching and I find CloudFlare doesn’t seem cache these direct images either. Also I’d assume this would disable image manipulation on any other images you might have.