• sharp (https://github.com/lovell/sharp)
• chromeless (https://github.com/graphcool/chromeless)

Meant to replace a phantomjs-based solution that is complicated to maintain. This is way less code and way more modern and efficient.

If you're here, you know what it's about. Clone, yarn/npm install and run node index.js after having tweaked parameters.

I did a test on 145 PNG images, resizing them all in one go takes 23s, an average of 1/6th of a second per file. This is of cours a ballpark estimate with a larger number of files resized at the same time and should only give a rough estimate of the running time per file.

• Transform into Express application
• See if more sizes can be cut concurrently
• See if more screenshots can be taken concurrently
• Deploy to GAE