Contentful assets size query parameter

I am following this blog

At Changing the image formats it gives the possibility to query the size by adding ?fm={image_format}. What is a correct format for the image_format? I have tried ?fm=100, ?fm=100mb ?fm=100%20MB, ?fm=true, but nothing works correctly…

Never mind. The answer are the strings ‘png’ or ‘webp’. It converts them to a different type, but it’s core function is not to change the size.