title: How do I animate in/out a gaussian blur effect in iOS?
body: <p>For the whole iOS 7 feel, I want to apply a blur effect to a specific portion of the screen to obfuscate it, but I don't want to just throw the blur on instantly, I want to animate it in and animate it out so the user almost sees the blur effect being applied.</p>
  
  <p>Almost as if in Photoshop you changed the gaussian blur value bit by bit from 0 to 10, instead of 0 to 10 in one go.</p>
  
  <p>I've tried a few solutions to this, the most popular suggestion being to simply put the blurred view on top of a non-blurred view, and then lower the alpha value of the blurred view.</p>
  
  <p>This works <em>okay</em>, but not very eye pleasing as there's no transition, it's just an overlay. Example:</p>
  
  <p><img src="https://i.stack.imgur.com/caYOf.png" alt="enter image description here"></p>
  
  <p>What would be a better way to achieve such an effect? I'm familiar with <a href="https://github.com/BradLarson/GPUImage" rel="noreferrer">GPUImage</a>, but not sure how to accomplish it with that.</p>
  
  <p>It'd also be great if I could control what percentage of the blur it is at, so it could be applied interactively from the user. (e.g.: user drags halfway, the blur is half applied, etc.)</p>