iOS Gray Scale Image - Swift

GrayScaleImage.swift

class Utils
{
    static func toGreyish(image:UIImage) -> UIImage?
    {
        guard let colorControlsFilter = CIFilter(name: "CIColorControls") else { return nil }
        guard let colorExposureFilter = CIFilter(name:"CIExposureAdjust") else { return nil }
        
        let ciImage = CIImage(image:image)
        
        colorControlsFilter.setValue(ciImage, forKey: kCIInputImageKey)
        colorControlsFilter.setValue(0.0, forKey: kCIInputBrightnessKey)
        colorControlsFilter.setValue(0.0, forKey: kCIInputSaturationKey)
        colorControlsFilter.setValue(1.0, forKey: kCIInputContrastKey)
        
        let intermediateImage = colorControlsFilter.outputImage
        
        colorExposureFilter.setValue(intermediateImage, forKey: kCIInputImageKey)
        colorExposureFilter.setValue(0.8, forKey: kCIInputEVKey)
        
        if let output = colorExposureFilter.outputImage
        {
            let context = CIContext(options: nil)
            let cgImage = context.createCGImage(output, fromRect: output.extent)
            return UIImage(CGImage: cgImage, scale: image.scale, orientation: image.imageOrientation)
        }
        
        return nil
    }
}

import UIKit
extension UIImage
{
    var greyish : UIImage? {
        return Utils.toGreyish(self)
    }
}

import UIKit
extension UIImageView
{
    func toGreyish()
    {
        guard let currentImage = self.image else {
            print("ImageView doesn't have an image to make greyish")
            return
        }
        let greyishImage = currentImage.greyish
        self.image = greyishImage
    }
}