function overlayHeight () {
	var scr_h = $(document).height();
	document.getElementById('fade').style.height = scr_h + 'px';
}

function popUp (a,c) {
    $('#' + a).show();
	document.getElementById('fade').style.display='block'; 
	overlayHeight();
	popUpPositon (a);
}

function popUpClose (b) {
	$('#' + b).hide();
	document.getElementById('fade').style.display='none'; 

}

function popUpPositon (c) {
    var imgWidth = $('#' +c).width();
    var imgHeight = $('#' +c).height();
    $('#' +c)
	    .css({
		    'top':        '50%',
		    'left':       '50%',				
		    'width':      imgWidth,
		    'height':     imgHeight,
		    'margin-top': -(imgHeight/2),
		    'margin-left':-(imgWidth/2) //to position it in the middle		
});
}