function popup(myurl,myname,mywidth,myheight,myoptions) {
    var window_top = (screen.height-myheight)/2;
    var window_left = (screen.width-mywidth)/2;
   	var mywindow = window.open(''+ myurl + '',''+ myname + '','width=' + mywidth + ',height=' + myheight + ',top=' + window_top + ',left=' + window_left + ',' + myoptions + '');
    mywindow.focus();
}

function changeimg(myid,myimg)
{
document.getElementById(''+myid+'').src = myimg;
}