Playing with CIColorControls filter

GrayScale.swift

    func applyGrayScaleFilter(image: UIImage?) -> UIImage? {
        guard let ciImage = image?.ciImage else { return nil }
        let filter = CIFilter(name: "CIColorControls",
                              parameters: ["inputImage" : ciImage,
                                           "inputContrast": NSNumber(1.0),
                                           "inputSaturation": NSNumber(0.0),
                                           "inputBrightness": NSNumber(0.0)])
        guard let out = filter?.outputImage else { return nil }
        return UIImage(ciImage: out)
    }