function rollIn(imageName) {
  if(!document.images) return;
  document.images[imageName].src = eval(imageName + "On.src");
}

function rollOut(imageName) {
  if(!document.images) return;
  document.images[imageName].src = eval(imageName + "Off.src");
}

var backOn = new Image();
backOn.src = "images/common/btn-back-hover.png";
var backOff = new Image();
backOff.src = "images/common/btn-back.png";
var nextOn = new Image();
nextOn.src = "images/common/btn-next-hover.png";
var nextOff = new Image();
nextOff.src = "images/common/btn-next.png";


var watchOn = new Image();
watchOn.src = "images/common/btn-watch-hover.png";
var watchOff = new Image();
watchOff.src = "images/common/btn-watch.png";

var ownerOn = new Image();
ownerOn.src = "images/common/btn-owner-hover.png";
var ownerOff = new Image();
ownerOff.src = "images/common/btn-owner.png";

var returnOn = new Image();
returnOn.src = "images/common/btn-return-hover.png";
var returnOff = new Image();
returnOff.src = "images/common/btn-return.png";