function gal_hover(_id)
{
  var image = document.getElementById('gal_id_img_' + _id);
  var preview = document.getElementById('gal_id_pre_' + _id);
  image.className = 'image_on';
  preview.className = 'image_off';

}

function gal_unhover(_id)
{
  var image = document.getElementById('gal_id_img_' + _id);
  var preview = document.getElementById('gal_id_pre_' + _id);
  image.className = 'image_off';
  preview.className = 'image_on';

}