title: When to add properties using CGImageDestinationSetProperties and when to add properties with CGImageDestinationAddImage
body: <p>I've been looking at creating gif file using CGImageDestinationRef and I haven't been able to find any documentation on which properties I should be applying using CGImageDestinationSetProperties and which properties I should be setting when I add an image to the CGImageDestination object using CGImageDestinationAddImage.</p>
  
  <p>But I realised this problem doesn't just apply to exporting image files as GIF files.</p>
  
  <p>I've looked at some properties returned by CGImageSource and though that supplies some clues it is hit &amp; miss. But for example it seems HasGlobalColorMap and LoopCount should be properties set using CGImageDestinationSetProperties whilst UnclampedDelayTime and DelayTime are properties that should be set when adding an image.</p>
  
  <p>I'm after guidance as to which properties I should be adding to the CGImageDestinationRef directly and which ones should be added when I add an image?</p>
  
  <p>Thanks</p>