def getskyimg(self,chip):
        """
        Notes
        =====
        Return an array representing the sky image for the detector.  The value
        of the sky is what would actually be subtracted from the exposure by
        the skysub step.

        :units: electrons

        """
        sci_chip = self._image[self.scienceExt,chip]
        return np.ones(sci_chip.image_shape,dtype=sci_chip.image_dtype)*sci_chip.subtractedSky