title: cast SKSpriteNode to UIImage
body: <p>I want to convert a SKSpriteNode into an UIImage.</p>
  
  <pre><code>let testImage = SKSpriteNode(imageNamed: "PlainProject") as! UIImage
  </code></pre>
  
  <p>but I get a crash on the thread above.  Is there another way to do this?</p>