code: def threshold_image(img, bkground_thresh, bkground_value=0.0):
      
  
      if bkground_thresh is None:
          return img
  
      if isinstance(bkground_thresh, str):
          try:
              thresh_perc = float(bkground_thresh.replace('%', ''))
          except:
              raise ValueError(
                  'percentile specified could not be parsed correctly '
                  ' - must be a string of the form "5%", "10%" etc')
          else:
              thresh_value = np.percentile(img, thresh_perc)
      elif isinstance(bkground_thresh, (float, int)):
          thresh_value = bkground_thresh
      else:
          raise ValueError('Invalid specification for background threshold.')
  
      img[img < thresh_value] = bkground_value
  
      return img
docs: Thresholds a given image at a value or percentile.
  
      Replacement value can be specified too.
  
  
      Parameters
      -----------
      image_in : ndarray
          Input image
  
      bkground_thresh : float
          a threshold value to identify the background
  
      bkground_value : float
          a value to fill the background elements with. Default 0.
  
      Returns
      -------
  
      thresholded_image : ndarray
          thresholded and/or filled image