code: def histeq(arr, num_bins=256):
      """Performs an histogram equalization on ``arr``.
      This was taken from:
      http://www.janeriksolem.net/2009/06/histogram-equalization-with-python-and.html
  
      Parameters
      ----------
      arr : ndarray
          Image on which to perform histogram equalization.
      num_bins : int
          Number of bins used to construct the histogram.
  
      Returns
      -------
      result : ndarray
          Histogram equalized image.
      """
      # get image histogram
      histo, bins = np.histogram(arr.flatten(), num_bins, density=True)
      cdf = histo.cumsum()
      cdf = 255 * cdf / cdf[-1]
  
      # use linear interpolation of cdf to find new pixel values
      result = np.interp(arr.flatten(), bins[:-1], cdf)
  
      return result.reshape(arr.shape)
  
label_desc: Use image node_id 1 for calling a global function with example usage: histeq(arr, num_bins) and returns: result