Swift UIImage和UIimage.pngData返回两个不同的图像

MRE

import SwiftUI

struct SwiftUIView: View {
    
    func maskImage(image: UIImage, mask: UIImage) -> UIImage {
        let imageReference = image.cgImage!
        let maskReference = mask.cgImage!

        let width = maskReference.width
        let height = maskReference.height
        let bitsPerComponent = maskReference.bitsPerComponent
        let bitsPerPixel = maskReference.bitsPerPixel
        let bytesPerRow = maskReference.bytesPerRow

        let context = CGContext(
            data: nil,
            width: width,
            height: height,
            bitsPerComponent: bitsPerComponent,
            bytesPerRow: bytesPerRow,
            space: CGColorSpaceCreateDeviceGray(),
            bitmapInfo: CGImageAlphaInfo.none.rawValue
        )

        context!.draw(maskReference, in: CGRect(x: 0, y: 0, width: width, height: height))

        let maskImage = context!.makeImage()!

        let maskedReference = imageReference.masking(maskImage)!

        return UIImage(cgImage: maskedReference)
    }
    
    var body: some View {
        VStack {
            Image(uiImage: maskImage(image: UIImage(named: "uni")!, mask: UIImage(named: "mask")!))
                .background(.red)
            
            Image(uiImage: UIImage(data: maskImage(image: UIImage(named: "uni")!, mask: UIImage(named: "mask")!).pngData()!)!)
                .background(.red)
        }
    }
}

此代码屏蔽图像并返回UIImage

您可以在VStack中看到第一个映像是正确的.它显示了遮罩区域后面带有红色背景的遮罩图像.

在VStack的第二张图像中，您可以看到透明度消失了.

因此，我需要做的是将temp.pngData()上传到服务器，并期望能够查看保留了预览代码中所示透明度的PNG文件.但是，当文件被上传时，我得到的是没有透明度的原始文件.

怎么修？