如何在Windows UWP应用程序中组合png图像-保持透明度？

<Image x:Name="combinedImage" Stretch="Uniform" />

private async Task CombineImages()
{
    // 加载第一个图像
    var file1 = await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///Assets/image1.png"));
    var stream1 = await file1.OpenAsync(FileAccessMode.Read);
    var decoder1 = await BitmapDecoder.CreateAsync(stream1);

    // 加载第二个图像
    var file2 = await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///Assets/image2.png"));
    var stream2 = await file2.OpenAsync(FileAccessMode.Read);
    var decoder2 = await BitmapDecoder.CreateAsync(stream2);

    // 创建RenderTargetBitmap对象
    var renderTargetBitmap = new RenderTargetBitmap();
    await renderTargetBitmap.RenderAsync(new[] { decoder1, decoder2 });

    // 将组合后的图像设置给Image控件
    combinedImage.Source = renderTargetBitmap;
}