function schattig(what) {
 what.oldhref = what.src;
 var length = what.src.substr(what.src.lastIndexOf('/') + 1).length - 4;
 if(what.src.indexOf("_schatten") == -1) {
  what.src = "img/" + what.src.substr(what.src.lastIndexOf('/') + 1, length) + "_schatten.png";
 }
}

function unschattig(what) {
 what.src = what.oldhref;
}