Invert background image.

ViewController.swift

import UIKit

class ViewController: UIViewController {
    
    var imageView: UIImageView?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let screenSize: CGRect = UIScreen.mainScreen().bounds
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: Selector("imageTapped"))
        
        if let image = UIImage(named: "autumn.jpg") {
            imageView = UIImageView(image: image)
            imageView!.frame = screenSize
            imageView!.userInteractionEnabled = true
            imageView!.addGestureRecognizer(tapGestureRecognizer)
            view.addSubview(imageView!)
        }
    }
    
    func imageTapped() {
        let beginImage = CIImage(image: imageView!.image!)
        if let filter = CIFilter(name: "CIColorInvert") {
            filter.setValue(beginImage, forKey: kCIInputImageKey)
            let newImage = UIImage(CIImage: filter.outputImage!)
            imageView!.image = newImage
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}