When starting to work on our iCatalog.framework I stumbled upon an annoying problem, the same that you will face if you ever need to work with large images. “Large” meaning of a resolution sufficient to cover the entire screen of an iPad or potentially double that (horizontally and vertically) when dealing with Retina Resolution on a future iPad.
Imagine you have a UIScrollView that displays UIImageViews for the individual pages of a catalog or magazine style app. As soon as even one pixel of the following page comes on screen you instantiate (or reuse) a UIImageView and pop it into the scroll view’s content area. That works quite well in Simulator, but when you test this on the device you find that every time you try to page to the next page, there is a noticeable delay. This delay results from the fact that images need to be decompressed from their file incarnation to be rendered on screen. Unfortunately UIImage does this decompression at the very latest possible moment, i.e. when it is to be displayed.
Since adding a new view to the view hierarchy has to occur on the main thread, so does the decompression and subsequent rendering of the image on screen. This is where this annoying stutter or pause is stemming from. You can see the same on app store apps where scrolling through something stutters whenever a new image appears on screen.
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