C# 双击可在WP8中缩放图像？

我在ScrollViewer中有一个图像，我希望该图像在双击时缩放。它可以正确缩放，但问题在于scrollviewer。我希望ScrollViewer滚动到用户点击的位置。就像用户点击右下角一样，该部分将被放大，scrollviewer将滚动以使该点位于屏幕中央。这是我正在使用的代码

private void ImgHolder1_DoubleTap(object sender, System.Windows.Input.GestureEventArgs e)
{
    //If zoomed in, then zoom out
    if (isZoomed)
    {
        Img1.Width = Img1.Width / 1.5;
        Img1.Height = Img1.Height / 1.5;
        ImgHolder1.HorizontalScrollBarVisibility = ScrollBarVisibility.Disabled;
        isPowerZoomed = false;
    }
    //else zoom in
    else
    {
        Img1.Width = Img1.Width * 1.5;
        Img1.Height = Img1.Height * 1.5;
        ImgHolder1.HorizontalScrollBarVisibility = ScrollBarVisibility.Visible;
        isPowerZoomed = true;
    }

    //Scroll to offset
    Point p = e.GetPosition(sender as UIElement);
    ImgHolder1.ScrollToHorizontalOffset(p.X);
    ImgHolder1.ScrollToVerticalOffset(p.Y);
}

有人能帮我吗