def _initialize(self):
        """ Open from caffe weights """
        self._graph = tf.Graph()
        with self._graph.as_default():
            self._input_node = tf.placeholder(tf.float32, (self._batch_size, self._im_height, self._im_width, self._num_channels))
            weights = self.build_alexnet_weights()
            self._output_tensor = self.build_alexnet(weights)
            self._feature_tensor = self.build_alexnet(weights, output_layer=self._feature_layer)
            self._initialized = True