code: def nan_pixels(self):
          
          nan_px = np.where(np.isnan(np.sum(self.raw_data, axis=2)))
          nan_px = np.c_[nan_px[0], nan_px[1]]
          return nan_px
docs: Return an array of the NaN pixels.
  
          Returns
          -------
          :obj:`numpy.ndarray`
               Nx2 array of the NaN pixels