docstr: This function calculates the false positive map from binary 
  segmentation and reference maps
  
  :return: FP map
docstr_tok: ["This","function","calculates","the","false","positive","map","from","binary","segmentation","and","reference","maps",":","return",":","FP","map"]
code: def __FPmap(self):
      """
      This function calculates the false positive map from binary
      segmentation and reference maps
  
      :return: FP map
      """
      self.check_binary()
      return np.asarray((self.seg - self.ref) > 0.0, dtype=np.float32)
  
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 3 for calling the PairwiseMeasures obj's underlying member method code with example usage: obj.__FPmap() and returns: np