WPF中的ImageSource如何转成Bitmap

        private Bitmap BitmapImage2Bitmap(BitmapImage bitmapImage)
        {
            using (MemoryStream outStream = new MemoryStream())
            {
                BitmapEncoder enc = new BmpBitmapEncoder();
                enc.Frames.Add(BitmapFrame.Create(bitmapImage));
                enc.Save(outStream);
                System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(outStream);

                return new Bitmap(bitmap);
            }
        }