code: def normalise_one_one(image):
      """Image normalisation. Normalises image to fit [-1, 1] range."""
  
      ret = normalise_zero_one(image)
      ret *= 2.0
      ret -= 1.0
      return ret
  
file_path: DLTK/dltk/io/preprocessing.py
imports: from __future__ import unicode_literals
  from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import numpy
label_desc: Use image node_id 3 for calling a global function with example usage: normalise_one_one(image) and returns: ret