ViewController.swift

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var imageView: UIImageView!

    override func viewDidLoad() {
        super.viewDidLoad()

        let image = UIImage(named: "image-1.jpg")
        let monoImageOperation = MonoImageOperation(inputImage: image!)
        monoImageOperation.completionBlock = {
            DispatchQueue.main.async {
                self.imageView.image = monoImageOperation.outputImage
            }
        }
        let operationQueue = OperationQueue()
        operationQueue.addOperation(monoImageOperation)
    }
}