extension UIImage {
    func invertedImage() -> UIImage? {

        let img = CoreImage.CIImage(CGImage: self.CGImage)

        let filter = CIFilter(name: "CIColorInvert")
        filter.setDefaults()

        filter.setValue(img, forKey: "inputImage")

        let context = CIContext(options:nil)

        let cgimg = context.createCGImage(filter.outputImage, fromRect: filter.outputImage.extent())

        return UIImage(CGImage: cgimg)
    }
}