var imgObj, imgWidth, imgHeight, imgRatio, imgX, imgY;
var winWidth, winHeight, winRatio;

function getDimensions() {
	document.body.style.overflow = "hidden";
	imgObj = document.getElementById('bgImg');
	imgWidth = imgObj.width;
	imgHeight = imgObj.height;
	imgRatio = imgWidth / imgHeight;
	changeSize();
	imgObj.style.visibility = 'visible';
}

function changeSize() {
	if (typeof window.innerWidth != 'undefined') {
		winWidth = window.innerWidth;
		winHeight = window.innerHeight;
	} else if (typeof document.documentElement != 'undefined' && typeof document.documentElement.clientWidth != 'undefined' && document.documentElement.clientWidth != 0)	{
		winWidth = document.documentElement.clientWidth;
		winHeight = document.documentElement.clientHeight;
	} else {
		winWidth = document.getElementsByTagName('body')[0].clientWidth;
		winHeight = document.getElementsByTagName('body')[0].clientHeight;
	}
	winRatio = winWidth / winHeight;
	if (winRatio > imgRatio) {
		imgWidth = winWidth;
		if (imgRatio > 1) {
			imgHeight = parseInt(imgWidth / imgRatio);
		} else {
			imgHeight = parseInt(imgWidth * imgRatio);	
		}
	} else {
		imgHeight = winHeight;
		if (imgRatio < 1) {
			imgWidth = parseInt(imgHeight / imgRatio);
		} else {
			//alert(imgHeight + '--' + imgRatio);
			imgWidth = parseInt(imgHeight * imgRatio);	
		}
	}
	imgX = 0;
	imgY = 0;
	if (imgWidth > winWidth) imgX = 0 - parseInt((imgWidth - winWidth) / 2)
	if (imgHeight > winHeight) imgY = 0 - parseInt((imgHeight - winHeight) / 2)
	var w = imgWidth + 'px';
	var h = imgHeight + 'px';
	var x = imgX + 'px';
	var y = imgY + 'px';
	imgObj.style.left = x;
	imgObj.style.top = y;
	imgObj.style.width = w;
	imgObj.style.height = h;
}