text: def lum_contrast(clip, lum = 0, contrast=0, contrast_thr=127):
      """ luminosity-contrast correction of a clip """
      
      def fl_image(im):
          im = 1.0*im # float conversion
          corrected = im + lum + factor*(im-thr)
          corrected[corrected < 0] = 0
          corrected[corrected > 255] = 255
          return corrected.astype('uint8')
      
      return clip.fl_image(fl_image)
  