function apripopup(imgsrcdir) {
   var imgsrc = document.getElementById("img_big").src;
   var len_imgsrc = imgsrc.length;
   var start_imgsrc = imgsrc.lastIndexOf("/") + 1;
   var imgsrc = imgsrc.substring(start_imgsrc,len_imgsrc);

   var w = 679;
   var h = 505;
   var l = Math.floor((screen.width-w)/2);
   var t = Math.floor((screen.height-h)/2);
      window.open("prodotto_popup.asp?dir="+imgsrcdir+"&img=big"+ imgsrc,"","width=" + w + ",height=" + h + ",top=" + t + ",left=" + l);
 }