// init array and preloading the images

     navImg = new Array()
     navImg[0] = new Image()
     navImg[1] = new Image()
     navImg[2] = new Image()
     navImg[3] = new Image()
     navImg[4] = new Image()
     navImg[5] = new Image()
     navImg[6] = new Image()
     navImg[7] = new Image()
     navImg[0].src = "img/nav_home_off.jpg"
     navImg[1].src = "img/nav_home_on.jpg"
     navImg[2].src = "img/nav_func_off.jpg"
     navImg[3].src = "img/nav_func_on.jpg"
     navImg[4].src = "img/nav_visie_off.jpg"
     navImg[5].src = "img/nav_visie_on.jpg"
     navImg[6].src = "img/nav_contact_off.jpg"
     navImg[7].src = "img/nav_contact_on.jpg"

     // function changing the button-image

     function rollOver(imgName, n) {
         document.images[imgName].src = navImg[n].src
         return true;
     }