当我在swift中向上滑动时，如何缩小比例？

import UIKit

class ViewController: UIViewController, UIScrollViewDelegate {
    
    var scrollView: UIScrollView!
    var imageView: UIImageView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建UIScrollView
        scrollView = UIScrollView(frame: view.bounds)
        scrollView.delegate = self
        scrollView.contentSize = CGSize(width: view.bounds.width, height: view.bounds.height * 2)
        view.addSubview(scrollView)
        
        // 创建UIImageView并添加到UIScrollView中
        imageView = UIImageView(image: UIImage(named: "image"))
        imageView.contentMode = .scaleAspectFit
        imageView.frame = CGRect(x: 0, y: 0, width: view.bounds.width, height: view.bounds.height * 2)
        scrollView.addSubview(imageView)
        
        // 设置UIScrollView的缩放范围
        scrollView.minimumZoomScale = 0.5
        scrollView.maximumZoomScale = 1.0
    }
    
    // 返回要缩放的视图
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return imageView
    }
    
    // 缩放时调整UIImageView的大小
    func scrollViewDidZoom(_ scrollView: UIScrollView) {
        let imageViewSize = imageView.frame.size
        let scrollViewSize = scrollView.bounds.size
        
        let verticalPadding = imageViewSize.height < scrollViewSize.height ? (scrollViewSize.height - imageViewSize.height) / 2 : 0
        let horizontalPadding = imageViewSize.width < scrollViewSize.width ? (scrollViewSize.width - imageViewSize.width) / 2 : 0
        
        scrollView.contentInset = UIEdgeInsets(top: verticalPadding, left: horizontalPadding, bottom: verticalPadding, right: horizontalPadding)
    }
}