function gallery(URL) { 
        
var w=800; 
var h=600; 
var ch=10;
var cw=10;

if (window.screen) { 

   w = parseInt(window.screen.availWidth * 0.90); 
   h = parseInt(window.screen.availHeight * 0.90); 
   cw = parseInt((window.screen.availWidth - w) /2);
   ch = parseInt(((window.screen.availHeight - h) /2) * 0.70);
   
} 

(w < 800) ? w = 800 : w = w; 
(h < 600) ? h = 600 : h = h; 

window.open(URL,'windowName','width='+w+',height='+h+',top='+ch+',left='+cw);

}