using System.Windows.Interop; 
//...

// Convert BitmapImage to Bitmap
private Bitmap BitmapImage2Bitmap(BitmapImage bitmapImage)
 {

        return new Bitmap(bitmapImage.StreamSource);

 }

    

// Convert Bitmap to BitmapImage

 private BitmapImage Bitmap2BitmapImage(Bitmap bitmap)

 {                

      BitmapSource i = Imaging.CreateBitmapSourceFromHBitmap(bitmap.GetHbitmap(),IntPtr.Zero,Int32Rect.Empty,BitmapSizeOptions.FromEmptyOptions());

      return (BitmapImage)i;

 }