code: def _normalize(image, mean_rgb=MEAN_RGB, stddev_rgb=STDDEV_RGB):
      """Normalizes images to variance 1 and mean 0 over the whole dataset"""
  
      image -= tf.broadcast_to(mean_rgb, tf.shape(image))
      image /= tf.broadcast_to(stddev_rgb, tf.shape(image))
  
      return image
  
label_desc: Use image node_id 2 for calling a global function with example usage: _normalize(image, mean_rgb, stddev_rgb) and returns: image