function roll(img_name, img_src)
   {
   document[img_name].src = img_src;
   }

function roll2(img_name, img_src, big_img_src)
   {
   document[img_name].src = img_src;
   document.getElementById('vismain').href = big_img_src;
   }

function roll3(img_name, img_src, big_img_src, desc)
   {
   document[img_name].src = img_src;
   document.getElementById('vismain').href = big_img_src;
   document.getElementById('photodesc').innerHTML = desc;
   }