function zoom_in_img(idth) {
 if (parseInt(idth.style.top)>-5) {
   idth.style.top   = parseInt(idth.style.top)-1;
   zoom_in=setTimeout(function(){zoom_in_img(idth)},0);
   }
 }

function zoom_out_img(idth) {
 clearTimeout(zoom_in);
 idth.style.top  = 0;
 }