// pre-load img
if (document.img) 
{
   img1 = new Image();
   img2 = new Image();
   img3 = new Image();
   img4 = new Image();
   img5 = new Image();
   img6 = new Image();
   img7 = new Image();
   img8 = new Image();
   img9 = new Image();
   img10 = new Image();
   img11 = new Image();
   img12 = new Image();
   img13 = new Image();
   img14 = new Image();
   img1.src = "img/yellowBL.gif";
   img2.src = "img/yellowBR.gif";
   img3.src = "img/yellowTL.gif";
   img4.src = "img/yellowTR.gif";
   img5.src = "img/purpleBL.gif";
   img6.src = "img/purpleBR.gif";
   img7.src = "img/purpleTL.gif";
   img8.src = "img/purpleTR.gif";
   img9.src = "img/oliveBL.gif";
   img10.src = "img/oliveBR.gif";
   img11.src = "img/oliveTL.gif";
   img12.src = "img/oliveTR.gif";
   img13.src = "img/yellowTL_home.gif";
   img14.src = "img/yellowTR_home.gif";
}