Full background image that can scroll (initially fixed)

I am trying to come up with a website of my own where I have a background image that covers the entire page when it loads initially. I want this to be responsive as well so that I can see the entire background image irrespective of screen size.

Here is the catch though, As I scroll the page I want the next div or element to be ready just below (on scrolling). The best reference i can think of right away would be fiftythree.com.