title: Core graphics stroke around existing, irregular image?
body: <p>Is it possible to take a pre-existing UIImage of an irregular shape, like the silhouette of an island or a user-drawn blob, and then use Core Graphics to draw an outline of a given width and color along its edges? I'm assuming an otherwise transparent UIImage, with a single solid shape. Interior or exterior strokes are acceptable, although exterior is preferred. </p>
  
  <p>It seems like that ought to be possible, but I'm a CG newbie and all of my research is just turning up tutorials and answers about adding stroke to an image as it is being drawn, or else along a simple, pre-defined path that can be hard-coded.  I'm finding surprisingly little information about dealing with irregular images based on the method's input.</p>
  
  <p>I know the SO community prefers code samples and such, but I honestly don't know where to start.  My only conceptual lead is, if it's possible to get a path based on the outline of an existing shape, I could stroke that path?  But I don't know how to get a path based on an irregular, unpredictable input image.</p>
  
  <p>Can anyone help a newbie out?</p>