def getReadNoiseImage(self, chip):
        """
        Notes
        =====
        Method for returning the readnoise image of a detector
        (in electrons).

        The method will return an array of the same shape as the image.

        :units: electrons

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