var win=null;
function mostrarimagen(url_imagen,titulo,ancho,alto){
var img = new Image();
win=window.open('','','width='+ancho+',height='+alto+',scrollbars=no,resizable=0,toolbar=0');
win.document.write ('\n');
win.document.write (' \n');
win.document.write (' '+titulo+'\n');
win.document.write (' \n');
win.document.write (' \n');
win.document.write (' 
\n');
win.document.write (' \n');
win.document.write ('\n');
}