function toPixelData(node, options) {
    return draw(node, options || {}).then(function (canvas) {
      return canvas.getContext('2d').getImageData(0, 0, util.width(node), util.height(node)).data
    })
  }
@param {Node} node - The DOM Node object to render
@param {Object} options - Rendering options, @see {@link toSvg}
@return {Promise} - A promise that is fulfilled with a Uint8Array containing RGBA pixel data.