使用可写位图调整图像大小不起作用

我正在使用Windows Phone CameraCaptureTask来收集图像，然后调整其大小以便在我的应用程序中更好地使用。出于某种原因，无论我尝试什么，我都无法调整图像大小。

主页.xaml.cs

private void cameraTask_Completed(object sender, PhotoResult e)
{
    if (e.TaskResult == TaskResult.OK)
    {
        BitmapImage bmi = new BitmapImage();
        bmi.SetSource(e.ChosenPhoto);
        //MessageBox.Show(bmi.PixelWidth.ToString() + "x" + bmi.PixelHeight.ToString());
        var gcd = GCD(bmi.PixelWidth, bmi.PixelHeight);
        var result = string.Format("{0}:{1}", bmi.PixelWidth / gcd, bmi.PixelHeight / gcd);
        WriteableBitmap wb = new WriteableBitmap(bmi);
        //WriteableBitmap wb;
        //Stream stream = new MemoryStream();
        var stream = new MemoryStream();

        switch (result)
        {
            case "3:4":
                //wb = new WriteableBitmap(480, 640);
                //wb.SetSource(e.ChosenPhoto);
                wb.SaveJpeg(stream, 480, 640, 0, 100);
                break;
            case "4:3":
                //wb = new WriteableBitmap(640, 480);
                //wb.SetSource(e.ChosenPhoto);
                wb.SaveJpeg(stream, 640, 480, 0, 100);
                break;
            case "9:16":
                //wb = new WriteableBitmap(448, 800);
                //wb.SetSource(e.ChosenPhoto);
                wb.SaveJpeg(stream, 448, 800, 0, 100);
                break;
            case "16:9":
                //wb = new WriteableBitmap(800, 448);
                //wb.SetSource(e.ChosenPhoto);
                wb.SaveJpeg(stream, 800, 448, 0, 100);
                break;
            default:
                wb = null;
                return;
        }
        stream.Seek(0, SeekOrigin.Begin);
        //stream.Dispose();
        MessageBox.Show(wb.PixelWidth.ToString() + " x " + wb.PixelHeight.ToString());
        var capturedPicture = new CapturedPicture(e.OriginalFileName, stream);
    }
}
public int GCD(int a, int b)
{
    while (a != 0 && b != 0)
    {
        if (a > b)
            a %= b;
        else
            b %= a;
    }
    if (a == 0)
        return b;
    else
        return a;
}

无论我做什么，将WriteableBitmap设置为 e.ChosenPhoto 或 bmi 都会强制生成的wb为原始大小。有什么想法吗？

wb = wb.Resize(Convert.ToInt32(pass value of width here), Convert.ToInt32(pass value of height here), WriteableBitmapExtensions.Interpolation.Bilinear);