title: Display large images on iOS without precut tiles
body: <p>I'm building a camera application that saves the image data to a single JPEG file in the sandbox. The images average at about 2mb in size. </p>
  
  <p><strong>Problem :</strong> I cannot display the images in a photo viewer because having a few images in memory throws memory warnings and makes scrolling through the images very slow.</p>
  
  <p>I cannot split the image into tiles and save them to disk because that's even more expensive than displaying the single image. I tried splitting the image up into tiles upon capture, but on the 5S it took, on average, 5 1/2 seconds to save all the tiles to disk. It will only get worse from there as the app is executed on older devices. This is very bad because what if the user exists the app in the middle of the save? I will have missing tiles and no uncompressed original file to find missing tiles later.</p>
  
  <p><strong>Question :</strong> what's the best way to show a full sized image without causing memory issues and keeping the scrolling fast? Tons of camera applications on the App Store do this and the Photos app does this, there has to be a good solution.</p>
  
  <p><strong>Note</strong> : I'm currently showing a thumbnail of the image and then loading the full size image from disk in another thread. Once the full size image loading has finished, I present the full size image on the main thread. This removes the memory issues because I only have one full size image in memory at once, with two thumbnails, but still causes lagging on the scrollview because drawing the full size image in the main thread is still pretty expensive.</p>
  
  <p>I would greatly appreciate any input!</p>