@objc func doubleTap(gestureRecognizer: UITapGestureRecognizer) {

    if self.productScrollView.zoomScale == 1 {
        self.productScrollView.zoom(to: self.zoomRectForScale(scale: self.productScrollView.maximumZoomScale, center: gestureRecognizer.location(in: gestureRecognizer.view)), animated: true)
    } else {
        self.productScrollView.setZoomScale(1, animated: true)
    }

}

let tintView = UIView()
 tintView.backgroundColor = UIColor(white: 0, alpha: 0.5)
 tintView.frame = CGRect(x: 0, y: 0, width: imageView.frame.width,
 height: imageView.frame.height)
 imageView.addSubview(tintView)

let tintView = UIView()
tintView.backgroundColor = UIColor(white: 0, alpha: 0.5)
tintView.translatesAutoresizingMaskIntoConstraints = false
imageView.addSubview(tintView)
NSLayoutConstraint.activate([
        tintView.bottomAnchor.constraint(equalTo: imageView.bottomAnchor),
        tintView.leadingAnchor.constraint(equalTo: imageView.leadingAnchor),
        tintView.trailingAnchor.constraint(equalTo: imageView.trailingAnchor),
        tintView.topAnchor.constraint(equalTo: imageView.topAnchor),
        ])