code: def invalid_pixel_mask(self):
          
          # init mask buffer
          mask = np.zeros([self.height, self.width, 1]).astype(np.uint8)
  
          # update invalid pixels
          zero_pixels = self.zero_pixels()
          nan_pixels = self.nan_pixels()
          mask[zero_pixels[:, 0], zero_pixels[:, 1]] = BINARY_IM_MAX_VAL
          mask[nan_pixels[:, 0], nan_pixels[:, 1]] = BINARY_IM_MAX_VAL
          return BinaryImage(mask, frame=self.frame)
docs: Returns a binary mask for the NaN- and zero-valued pixels.
          Serves as a mask for invalid pixels.
  
          Returns
          -------
          :obj:`BinaryImage`
              Binary image where a pixel value greater than zero indicates an invalid pixel.