code: function (filename, fn) {
  
  		fn = fn || function () {};
  
  		this._image.pack().pipe(fs.createWriteStream(filename)).once('close', function () {
  			this._image.removeListener('error', fn);
  			fn(undefined, this);
  		}.bind(this)).once('error', function (err) {
  			this._image.removeListener('close', fn);
  			fn(err, this);
  		}.bind(this));
  	}
docs: Writes the image to the filesystem
  
  @method writeImage
  @param {string} filename Path to file
  @param {function} fn Callback