getDataImage to a node server

I'm trying to run an html5 canvas script on a node server. The ideas is to have a client page show a canvas with some simple animation/graphics and then send this image data (info about each pixel) to the server.

function draw() {   
    var canvas = document.getElementById("canvas");
    var ctx = canvas.getContext("2d");
    var socket = io.connect();

    canvas.addEventListener('mousemove', function(evt)
    {
        ctx.beginPath();
        ctx.moveTo(0, 0);
        ctx.lineTo(evt.clientX, evt.clientY);
        ctx.stroke();
        pixels = ctx.getImageData(0, 0, 400, 400);
        socket.emit('message', pixels);
    });   
 }

However, socket.emit causes the script (the animation in the canvas) to run too slow. The script is supposed to display a line from the origin (top left) to current mouse position. The lines are appearing but irregularly - a bunch of lines every 2 or 3 seconds. If I comment out the socket.emit, the sketch runs smoothly. This means that ctx.getImageData is not the one causing the delay.

Is there a way to send this information to the server without slowing down the script?

The pixel information sent to the server will later be used by a second client to populate its canvas. I'm trying to build something like a set of synchronized sketch - draw in one canvas and see the results in many. I'm really new to developing for the web so I'm not sure if this can even be done in real time.