title: How do I make a blur effect like a profile site on twitter?
body: <p>I am wondering how I can make a blur effect when I drag to the top of a UIScrollview like on twitter and in tweetbot. I have been looking around but I did not find it out anywhere. I know I have to use gaussian blur, but I don't know how I am going to implement it. Any code would be greatly appreciated. </p>
  
  <p><img src="https://i.stack.imgur.com/iIqgG.gif" alt="Twitter"></p>
  
  <p><img src="https://i.stack.imgur.com/LMeIa.gif" alt="Tweetbot"></p>