title: Qt reading many images optimization - how to only read the size?
body: <p>The title sums this one up. If I'm loading ~200 images of various size. How can I load just the header so I can know the size of each image?</p>
  
  <p>Currently I find it takes a lot of cpu/memory and IO to load them all in to memory just for the size (I'm trying to generate an atlas from them).</p>
  
  <p><code>QImage</code> doesn't seem to have a way to do this. <code>QImageReader</code> sounded like it was what I wanted, yet this still seems to just go ahead and read the whole image, so not really sure what its purpose is. Is there another class or some way to use either of the class I've mentioned to only grab the image size from header?</p>