function imgPreload (name, src) {
	var img = document.getElementById(name);
	if (!img) return;
	if (img.onImage) return;
	img.onImage = new Image();
	img.onImage.src = src;
}

function imgTurnOn (name, src) {
	var img = document.getElementById(name);
	if (!img) return;
	imgPreload(name, src);
	if (!img.onImage) return;
	if (!img.offImage) {
		img.offImage = new Image();
		img.offImage.src = img.src;
	}
	img.src = img.onImage.src;
}

function imgTurnOff (name) {
	var img = document.getElementById(name);
	if (!img) return;
	if (!img.offImage) return;
	img.src = img.offImage.src;
}

function turnOnImageAndLink (imgId, imgSrc, linkId, linkClassName) {
	imgPreload(imgId, imgSrc);
	imgTurnOn(imgId);
	var link = document.getElementById(linkId);
	if (typeof link != 'undefined') link.className = linkClassName;
}

function turnOffImageAndLink (imgId, linkId, linkClassName) {
	imgTurnOff(imgId);
	var link = document.getElementById(linkId);
	if (typeof link != 'undefined') link.className = linkClassName;
}