docstr: This function calculates the informedness between the segmentation
  and the reference
  
  :return: informedness
docstr_tok: ["This","function","calculates","the","informedness","between","the","segmentation","and","the","reference",":","return",":","informedness"]
code: def informedness(self):
      """
      This function calculates the informedness between the segmentation
      and the reference
  
      :return: informedness
      """
      return self.sensitivity() + self.specificity() - 1
  
imports: from __future__ import absolute_import, print_function
  import numpy
  from scipy import ndimage
  from niftynet.utilities.util_common import MorphologyOps, CacheFunctionOutput
label_desc: Use image node_id 28 for calling the PairwiseMeasures obj's underlying member method code with example usage: obj.informedness() and returns: unknown