https://api.xformmedia.com/image.jpg?w=800&q=85 Simply add the w=400 parameter to resize an image to 400 pixels wide while maintaining the aspect ratio.
https://my-images.xform.media/image.jpg?w=400 Use the h=300 parameter to resize an image to 300 pixels tall while maintaining the aspect ratio.
https://my-images.xform.media/image.jpg?h=300
Original: 1200x900px → Resized: 250x180px