get ImageData from a WebGL renderer

gistfile1.js

var img = document.createElement('img');
img.src = renderer.domElement.toDataURL('image/png');
img.onload = function() {
	var canvas = document.createElement('canvas');
	canvas.width = renderer.domElement.width;
	canvas.height = renderer.domElement.height;
	var ctx = canvas.getContext('2d');
	ctx.drawImage(img, 0, 0, img.naturalWidth, img.naturalHeight, 0, 0, canvas.width, canvas.height);
	var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
}