 class PhotoEditingViewController: UIViewController, PHContentEditingController {
   
   let filter = ChromaKeyFilter()
+  var includesChanges = false
   var input: PHContentEditingInput?
   let formatIdentifier = "com.shinobicontrols.chromakey"
   let formatVersion    = "1.0"

  var shouldShowCancelConfirmation: Bool {
    // Determines whether a confirmation to discard changes should be shown to the user on cancel.
    // (Typically, this should be "true" if there are any unsaved changes.)
    return false
  }
  
  func cancelContentEditing() {

  @IBOutlet weak var thresholdSlider: UISlider!
  @IBAction func handleThresholdSliderChanged(sender: UISlider) {
    updateOutputImage()
    includesChanges = true
  }
  
  override func viewDidLoad() {
