function viewportHeight()
{
    return self.innerHeight || (document.documentElement.clientHeight || document.body.clientHeight);
}

function check_bg()
{
	obj = document.getElementById('bg');
	bg_id = document.getElementById('wrap');
	page_height = viewportHeight();
	//console.log(page_height);

	var hide_x = false;
	var hide_y = false;

	width = obj.width;
	height = obj.height;

	if (document.body.clientHeight > page_height) hide_y = true;
	else hide_y = false;

	if (document.body.clientWidth > 920) hide_x = true;
	else hide_x = false;

	if (hide_x && hide_y) document.body.style.overflow = 'hidden';
	else document.body.style.overflow = '';

	if (hide_y) sh = document.body.clientHeight;
	else sh = page_height;

	if (hide_x)	sw = document.body.clientWidth;
	else sw = 920;

	bg_id.style.height = sh+'px';
	bg_id.style.width = sw+'px';

	if (sw >= 800 || sh >= 533)
	{
		sratio = sh / sw;
		pratio = height / width;

		if (sratio < pratio)
		{
			obj.style.height = '';
			obj.style.width = '100%';
		}
		else
		{
			obj.style.width = '';
			obj.style.height = '100%';
		}
	}
	else
	{
		obj.style.width = '';
		obj.style.height = '';
	}
/*
		document.getElementById('box1').innerHTML = 'width = '+width;
		document.getElementById('box2').innerHTML = 'height = '+height;
		document.getElementById('box3').innerHTML = 'd.b.cw = '+document.body.clientWidth;
		document.getElementById('box4').innerHTML = 'd.b.ch = '+document.body.clientHeight;
		document.getElementById('box5').innerHTML = 'sw = '+sw;
		document.getElementById('box6').innerHTML = 'sh = '+sh;*/

//	document.getElementById('bg_img_div').style.height = document.documentElement.scrollHeight+"px";
/*
	document.getElementById('box1').innerHTML = 'imgwidth = '+width;
	document.getElementById('box2').innerHTML = 'scrollWidth = '+document.documentElement.scrollWidth;
	document.getElementById('box3').innerHTML = 'clientWidth = '+document.documentElement.clientWidth;
	document.getElementById('box4').innerHTML = 'bg_div_width = '+bg_id.style.width;*/
}