service = new Image();
service.src = "img/button_service_n.jpg";
service_h = new Image();
service_h.src = "img/button_service_h.jpg";

partner = new Image();
partner.src = "img/button_partner_n.jpg";
partner_h = new Image();
partner_h.src = "img/button_partner_h.jpg";

produkte = new Image();
produkte.src = "img/button_produkte_n.jpg";
produkte_h = new Image();
produkte_h.src = "img/button_produkte_h.jpg";

anfrage = new Image();
anfrage.src = "img/button_anfrage_n.jpg";
anfrage_h = new Image();
anfrage_h.src = "img/button_anfrage_h.jpg";

function buttons (buttonnr, pictureobj) {
  window.document.images[buttonnr].src = pictureobj.src;
}