code: def _binary_array_to_hex(arr):
      """
      internal function to make a hex string out of a binary array.
      """
      bit_string = "".join(str(b) for b in 1 * arr.flatten())
      width = int(numpy.ceil(len(bit_string) / 4))
      return "{:0>{width}x}".format(int(bit_string, 2), width=width)
  
imports: from __future__ import absolute_import, division, print_function
  import sys
  import numpy
  from PIL import Image, ImageFilter
label_desc: Use image node_id 1 for calling a global function with example usage: _binary_array_to_hex(arr) and returns: str