def __init__(self,
               negative_example_distance,
               patch_width,
               negative_to_positive_example_ratio,
               noise_fn=lambda x: x):
    self.negative_example_distance = negative_example_distance
    self.patch_width = patch_width
    self.negative_to_positive_example_ratio = negative_to_positive_example_ratio
    self.noise_fn = noise_fn
    self.patch_counter = Metrics.counter(self.__class__, 'num_patches')