public static void DpiHack(BitmapSource img)
{
// a dirty hack... but is the fastest
var newDpiX = (double) DpiHelper.DefaultDpi * DpiHelper.GetCurrentScaleFactor().Horizontal;
var newDpiY = (double) DpiHelper.DefaultDpi * DpiHelper.GetCurrentScaleFactor().Vertical;
var dpiX = img.GetType().GetField("_dpiX",
BindingFlags.NonPublic | BindingFlags.Instance);
var dpiY = img.GetType().GetField("_dpiY",
BindingFlags.NonPublic | BindingFlags.Instance);
dpiX?.SetValue(img, newDpiX);
dpiY?.SetValue(img, newDpiY);
}