$(document).ready(function(){

    $('.viewer').mouseleave(function(){$(this).css({backgroundPosition: ('-100%  -100%')})});

    $('.viewer').mousemove(function(e){
    var bgheight=150;
    var bgwidth=400;
    var speedx=400;
    var speedy=0;
    var vH=$(this).height();

    var vW=$(this).width();

    var vT=$(this).offset().top;

    var vL=$(this).offset().left;

        var ypos=e.pageY-vT;

        var xpos=e.pageX-vL;

        var y=Math.round(ypos/vH*100);
        var x=Math.round(xpos/vW*100);
        //$(this).css({backgroundPosition: (xpos-(bgwidth/2)+((x-50)/100)*speedx)+'  '+(ypos-(bgheight/2)+((y-50)/100)*speedy)});
        $(this).css({backgroundPosition:(xpos-(bgwidth/2))+'  '+(ypos-(bgheight/2))});
    });

});