ImageBoss also supports image conversion on the fly.
If you want to convert the output image, use theoption. Just pass the option on the URL as explained below.
accepts jpg, png, webp and tiff.
https://img.imageboss.me /width /700 /http://imageboss.me/examples/02.jpg
This will convert your jpg image to png.
If you want to know more about WebP and how to use it properly check out Image Compression.