text: #!/usr/bin/env python
  #
  # Copyright (c) 2016 Matthew Earl
  # 
  # Permission is hereby granted, free of charge, to any person obtaining a copy
  # of this software and associated documentation files (the "Software"), to deal
  # in the Software without restriction, including without limitation the rights
  # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  # copies of the Software, and to permit persons to whom the Software is
  # furnished to do so, subject to the following conditions:
  # 
  #     The above copyright notice and this permission notice shall be included
  #     in all copies or substantial portions of the Software.
  # 
  #     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  #     OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  #     MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
  #     NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
  #     DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
  #     OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
  #     USE OR OTHER DEALINGS IN THE SOFTWARE.
  
  
  
  """
  Extract background images from a tar archive.
  
  """
  
  
  __all__ = (
      'extract_backgrounds',
  )
  
  
  import os
  import sys
  import tarfile
  
  import cv2
  import numpy
  
  
  def im_from_file(f):
      a = numpy.asarray(bytearray(f.read()), dtype=numpy.uint8)
      return cv2.imdecode(a, 0)
  
  
  def extract_backgrounds(archive_name):
      """
      Extract backgrounds from provided tar archive.
  
      JPEGs from the archive are converted into grayscale, and cropped/resized to
      256x256, and saved in ./bgs/.
  
      :param archive_name:
          Name of the .tar file containing JPEGs of background images.
  
      """
      os.mkdir("bgs")
  
      t = tarfile.open(name=archive_name)
  
      def members():
          m = t.next()
          while m:
              yield m
              m = t.next()
      index = 0
      for m in members():
          if not m.name.endswith(".jpg"):
              continue
          f =  t.extractfile(m)
          try:
              im = im_from_file(f)
          finally:
              f.close()
          if im is None:
              continue
          
          if im.shape[0] > im.shape[1]:
              im = im[:im.shape[1], :]
          else:
              im = im[:, :im.shape[0]]
          if im.shape[0] > 256:
              im = cv2.resize(im, (256, 256))
          fname = "bgs/{:08}.jpg".format(index)
          print (fname)
          rc = cv2.imwrite(fname, im)
          if not rc:
              raise Exception("Failed to write file {}".format(fname))
          index += 1
  
  
  if __name__ == "__main__":
  
      extract_backgrounds(sys.argv[1])
  
  