code: def averageSameExpTimes(imgs_path):
      '''
      average background images with same exposure time
      '''
      firsts = imgs_path[:2]
      imgs = imgs_path[2:]
      for n, i in enumerate(firsts):
          firsts[n] = np.asfarray(imread(i))
      d = DarkCurrentMap(firsts)
      for i in imgs:
          i = imread(i)
          d.addImg(i)
      return d.map(f averageSameExpTimes(imgs_path):
      '''
      average background images with same exposure time
      '''
      firsts = imgs_path[:2]
      imgs = imgs_path[2:]
      for n, i in enumerate(firsts):
          firsts[n] = np.asfarray(imread(i))
      d = DarkCurrentMap(firsts)
      for i in imgs:
          i = imread(i)
          d.addImg(i)
      return d.map()
docs: average background images with same exposure time