Source code for facereclib.tools.LGBPHS

#!/usr/bin/env python
# vim: set fileencoding=utf-8 :
# Manuel Guenther <Manuel.Guenther@idiap.ch>

import bob.math

import numpy

from .Tool import Tool
from .. import utils

class LGBPHS (Tool):
  """Tool chain for computing local Gabor binary pattern histogram sequences"""

  def __init__(
      self,
      distance_function = bob.math.chi_square,
      is_distance_function = True,
      multiple_probe_scoring = 'average'
  ):
    """Initializes the local Gabor binary pattern histogram sequence tool"""

    # call base class constructor
    Tool.__init__(
        self,

        distance_function = str(distance_function),
        is_distance_function = is_distance_function,

        multiple_model_scoring = None,
        multiple_probe_scoring = multiple_probe_scoring
    )

    # remember distance function
    self.m_distance_function = distance_function
    self.m_factor =  -1. if is_distance_function else 1

  def enroll(self, enroll_features):
    """Enrolling model by taking the average of all features"""
    sparse = len(enroll_features) > 0 and enroll_features[0].shape[0] == 2
    if sparse:
      # get all indices for the sparse model
      values = {}
      # assert that we got sparse features
      assert enroll_features[0].shape[0] == 2
      # iterate through all sparse features
      for i in range(len(enroll_features)):
        feature = enroll_features[i]
        # collect the values by index
        for j in range(feature.shape[1]):
          index = int(feature[0,j])
          value = feature[1,j] / float(len(enroll_features))
          # add up values
          if index in values:
            values[index] += value
          else:
            values[index] = value

      # create model containing all the used indices
      model = numpy.ndarray((2, len(values)), dtype = numpy.float64)

      i = 0
      for index in sorted(values.keys()):
        model[0,i] = index
        model[1,i] = values[index]
        i += 1
    else:
      model = numpy.zeros(enroll_features[0].shape, dtype = numpy.float64)
      # add up models
      for i in range(len(enroll_features)):
        model += enroll_features[i]
      # normalize by number of models
      model /= float(len(enroll_features))

    # return averaged model
    return model


  def score(self, model, probe):
    """Computes the score using the specified histogram measure; returns a similarity value (bigger -> better)"""
    sparse = model.shape[0] == 2
    if sparse:
      # assure that the probe is sparse as well
      sparse_probe = utils.histogram.sparsify(probe)
      return self.m_factor * self.m_distance_function(model[0,:], model[1,:], sparse_probe[0,:], sparse_probe[1,:])
    else:
      return self.m_factor * self.m_distance_function(model.flatten(), probe.flatten())