code: def adjust_contrast(image, factor):
      """Adjust contrast of an image.
  
      Args
          image: Image to adjust.
          factor: A factor for adjusting contrast.
      """
      mean = image.mean(axis=0).mean(axis=0)
      return _clip((image - mean) * factor + mean)
  
imports: from __future__ import division
  import numpy
  import cv2
  from PIL import Image
  from .transform import change_transform_origin
label_desc: Use image node_id 11 for calling a global function with example usage: adjust_contrast(image, factor) and returns: _clip