img = new Array("images/b_01.gif","images/b_01b.gif","images/b_02.gif","images/b_02b.gif","images/b_03.gif","images/b_03b.gif","images/b_04.gif","images/b_04b.gif","images/b_05.gif","images/b_05b.gif","images/b_06.gif","images/b_06b.gif","images/b_07.gif","images/b_07b.gif");
bfImg = new Array();
for(i=0; i<img.length; i++) {
  bfImg[i] = new Image();
  bfImg[i].src = img[i];
}