AMP images and page load speed relation

I presume when we have big (heavy) images on a webapge, it slows the webpage speed. AMP requires 1200 as minimum for width. When we don't actually need that large an image on the page, how advisable is to to have that large an image as that will affect page speed adversly. Am I correct in understanding this relation? How do we overcome this scenario as we of course would want images as per Google defined AMP specifications and also manitain the page speed at the same time?