title: swift generate qr code with transparent background
body: <p>in my swift 2 app i can generate a QR Code like this:</p>
  
  <pre><code>let data = "1234567890".dataUsingEncoding(NSISOLatin1StringEncoding, allowLossyConversion: false)
  let filter = CIFilter(name: "CIQRCodeGenerator")
  filter!.setValue(data, forKey: "inputMessage")
  filter!.setValue("Q", forKey: "inputCorrectionLevel")
  qrcodeImage = filter!.outputImage
  let transformedImage = qrcodeImage.imageByApplyingTransform(CGAffineTransformMakeScale(150, 150))
  QRCodeImage.image = UIImage(CIImage: transformedImage)
  </code></pre>
  
  <p>but my QR Code get an white background image, but i would like to have an transparent background.</p>
  
  <p>i tried something like this:</p>
  
  <pre><code>QRCodeImage.backgroundColor = UIColor.clearColor()
  </code></pre>
  
  <p>but this doesn't work.
  any idea ? :)</p>