code: def getdarkimg(self,chip):
          
          sci_chip = self._image[self.scienceExt,chip]
          return np.ones(sci_chip.image_shape,dtype=sci_chip.image_dtype)*sci_chip.darkcurrent
docs: Notes
          =====
          Return an array representing the dark image for the detector.
  
          The method will return an array of the same shape as the image.
  
          :units: electrons