function zoom(largeur,hauteur,options) {
	var top = (screen.height-hauteur)/2;
	var left = (screen.width-largeur)/2;
    window.open("/zoom.php?id="+id_annonce+"&num_photo="+photo,"","top="+top+",left="+left+",width="+largeur+",height="+hauteur+","+options);
}

function change_photo(increment) {
    
    photo = photo + increment;

    if(photo > nb_photos)
        photo = 1;
        
    if(photo <= 0)
        photo = nb_photos;
            
    if(nb_photos > 0)
        document.getElementById("img").src = "photos/"+montab[photo];
}