function OpenPopUp( Filename, Width, Height, AltText ) {
  var PopUp = document.getElementById("PopUp");
  
  var Fensterbreite = document.documentElement.clientWidth;
  var Center = (( Fensterbreite - Width ) / 2);
  PopUp.innerHTML = "<img src=\"" + Filename + "\" width=\"" + Width + "\" height=\"" + Height + "\" alt=\"" + AltText + "\" title=\"" + AltText + "\" />";
  PopUp.style.left    = Center + "px";
  PopUp.style.display = "block";
} // OpenPopUp

function ClosePopUp( ) {
  var PopUp = document.getElementById("PopUp");
  PopUp.style.display = "none";
} //