private void erodeToolStripMenuItem1_Click(object sender, EventArgs e) //Erode
        {
            if (img == null)                                                   // verify if the image is already opened
            {
                return;
            }
            Cursor = Cursors.WaitCursor; // clock cursor

            //copy Undo Image
            imgUndo = img.Copy();

            MIplImage s = imgUndo.MIplImage;


            ImageClass.Erode(img, imgUndo);



            ImageViewer.Image = img.Bitmap;
            ImageViewer.Refresh();    // refresh image on the screen

            Cursor = Cursors.Default; // normal cursor
        }