function showImage(obj){
    var imgwidth = 400;
		var mainwidth = 768;
		
		var main = window.document.getElementById("main")
		var div = window.document.getElementById('imageviewer');

		//wenn nicht existiert
		if(!div){
			var html = '';
		
  		html += '<div id="imageviewer" style="display:none;">';
			html += '<div><img src="/script/img/close.gif" alt="schlie&szlig;en" onClick="hideImage()"></div>';
  		html += '<img src="'+obj.src+'" alt="'+obj.alt+'" width="'+imgwidth+'" id="imageviewer_img">';
			html += '<div id="imageviewer_desc"></div>';
  		html += '</div>';
  		
  		main.innerHTML += html;
			div = window.document.getElementById('imageviewer');
		}
		
		var img = window.document.getElementById('imageviewer_img');
		var desc = window.document.getElementById('imageviewer_desc');
		
		//Einstellungen
		img.src = obj.src;
		img.alt = obj.alt;
		desc.innerHTML = obj.alt;
		div.style.top = (120+scrollOffsetTop())+'px';
		div.style.left = (mainwidth-imgwidth)/2;
		
		//anzeigen
		div.style.display = 'block';
		
}

function hideImage(){
    var div = window.document.getElementById('imageviewer');
		if(div){
		    div.style.display = 'none';
		}		 
}

function scrollOffsetTop(){
  var y;
	// all except Explorer
  if (self.pageYOffset) 
  {
  	y = self.pageYOffset;
  }
	// Explorer 6 Strict
  else if (document.documentElement && document.documentElement.scrollTop)
  {
  	y = document.documentElement.scrollTop;
  }
	// all other Explorers
  else if (document.body) 
  {
  	y = document.body.scrollTop;
  }
	//restliche Browser
	else{
	  y = window.pageYOffset;
	}
	
	return y;
}