var max_x = 320;
var max_y = 360;
        
       

function redim(iobj)
{
    if ( iobj.width >= iobj.height )    //més ample o igual que alt
    {
        if ( iobj.width > max_x )
        {
            var factor = iobj.height / iobj.width;
            iobj.width = max_x;
            iobj.height = max_x * factor;                    
        }
    }else if (iobj.height > iobj.width ){                              //més alt que ample
        if ( iobj.height > max_y )
        {
            var factor = iobj.width / iobj.height;
            iobj.height = max_y;
            iobj.width = max_y * factor;
         }
    }
    iobj.style.visibility = "visible";
}