Imageconvert

This is a commandline tool which creates images in different resolutions and writes them to a output directory

Currently it automatically creates and optimizes the images to the following resolutions:

640px 1536px 2048px 2880px

It's based on Graphicsmagick. So you need to install it first.

Under MacOSX ( you should have homebrew installed ) brew install graphicsmagick --with-webp