var onImg = new Array();
var offImg = new Array();
for (var i = 0; i < imageNames.length; i++) {
	refName = imageNames[i];
// The image which's name start with 'ub' and end with two numbers can use the same swap image: eg. ubup01, unup02 -> up.gif up_on.gif , ubdown01 ubdown03 -> down.gif down_on.gif
	if (refName.substr(0,2)=='ub') {
		imgName = imageDir + refName.substr(2,refName.length-4) + ".gif";
		imgHLName = imageDir + refName.substr(2,refName.length-4) + "_on.gif";
	} else {
		imgName = imageDir + refName + ".gif";
		imgHLName = imageDir + refName + "_on.gif";
	}
	onImg[refName] = new Image();
	offImg[refName] = new Image();
	onImg[refName].src = imgHLName;
	offImg[refName].src = imgName;
}