docstr: Alter the Contrast of an image with a value randomly selected
  between `min_val` and `max_val`
  
  Arguments
  ---------
  min_val : float
      min range
  max_val : float
      max range
code: def __init__(self, min_val, max_val):
      """
      Alter the Contrast of an image with a value randomly selected
      between `min_val` and `max_val`
  
      Arguments
      ---------
      min_val : float
          min range
      max_val : float
          max range
      """
      self.values = (min_val, max_val)
  
imports: import random
  import torch
  from torchvision.transforms.functional import to_tensor
  import numpy
  from ..utils import th_random_choice
label_desc: Use image node_id 1 to create a new RandomContrast object  with example: obj = RandomContrast(min_val, max_val)