function getPopupDistLeft(width){
	if (window.screen) {
		left = (screen.availWidth - width)/2;
	}
	else{
		left = (640-width)/2;
	}
	return(left);
}
function getPopupDistTop(height){
	if (window.event) {
		topPx = (screen.availHeight - height - 50)/2;
	}
	else{
		topPx = (480-height)/2;
	}
	return(topPx);
}
function getPopupScreenHeight(){
	var height = 520;
	if (window.screen) {
		height = screen.availHeight - 150;
	}
	else{
		height = 520;
	}
	if(height > 768) height = 768;
	return(height);
}
function  openpopuppage(id,collection){
//	alert("id: "+id+" collection: "+collection);
	var url = "/schilderij.php?id="+id+"&collection="+collection;
	var width = 640;
	var height = 520;
	if (window.screen) {
		height = screen.availHeight - 150;
	}
	else{
		height = 520;
	}
	if(height > 768) height = 768;
	eval("desktop = window.open('"+url+"','popuppage','width="+width+",height=520,left="+getPopupDistLeft(width)+",top=30,toolbar=no,location=no,status=yes,menubar=yes,scrollbars=yes,resizable=yes');");
}