function fenster(BildUrl,breite,hoehe) {
 var b=breite;
 var h=hoehe;
 var x=(screen.width/2)-(b/2);
 var y=(screen.height/2)-(h/2);
 window.open(BildUrl,'',"width="+b+",height="+h+",left="+x+",top="+y+",menubar=no,resizeable=no,location=no,status=no");
}