为什么当我减少图片中的像素数时,文件的大小会变大?

我正在尝试使用swift调整图像的大小。我一直在尝试将像素宽度设置为1080p。我使用的原始照片的宽度为1200像素,是一个760 KB的文件。使用以下函数调整图像大小以获得1080p后,结果为833kb。

    func resizeImage(image: UIImage, newWidth: CGFloat) -> UIImage {
    let scale = newWidth / image.size.width
    let newHeight = image.size.height * scale
    UIGraphicsBeginImageContext(CGSize(width: newWidth, height: newHeight))
    image.draw(in: CGRect(x: 0, y: 0, width: newWidth, height: newHeight))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return newImage! 
}

下面是完整的代码

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var imageView: UIImageView!
    var image:UIImage!

    override func viewDidLoad() {
        super.viewDidLoad()
        image = imageView.image
        let bcf = ByteCountFormatter()
        bcf.allowedUnits = [.useKB] // optional: restricts the units to MB only
        bcf.countStyle = .file
        var string = bcf.string(fromByteCount: Int64(image.jpegData(compressionQuality: 1.0)!.count))
        print("formatted result: \(string)")
        compressionLabel.text = string

        print("Image Pixels: \(CGSize(width: image.size.width*image.scale, height: image.size.height*image.scale))")

        image = resizeImage(image: image, newWidth: 1080)

        string = bcf.string(fromByteCount: Int64(image.jpegData(compressionQuality: 1.0)!.count))
        print("formatted result: \(string)")
        compressionLabel.text = string

        print("Image Pixels: \(CGSize(width: image.size.width*image.scale, height: image.size.height*image.scale))")
    }


    func resizeImage(image: UIImage, newWidth: CGFloat) -> UIImage {
        let scale = newWidth / image.size.width
        let newHeight = image.size.height * scale
        UIGraphicsBeginImageContext(CGSize(width: newWidth, height: newHeight))
        image.draw(in: CGRect(x: 0, y: 0, width: newWidth, height: newHeight))
        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage!

    }

}