docs: def _series_mdgel(self):
          """Return image series in MD Gel file."""
          # only a single page, scaled according to metadata in second page
          self.pages.useframes = False
          self.pages.keyframe = 0
          md = self.mdgel_metadata
          if md['FileTag'] in (2, 128):
              dtype = numpy.dtype('float32')
              scale = md['ScalePixel']
              scale = scale[0] / scale[1]  # rational
              if md['FileTag'] == 2:
                  # squary root data format
                  def transform(a):
                      return a.astype('float32')**2 * scale
              else:
                  def transform(a):
                      return a.astype('float32') * scale
          else:
              transform = None
          page = self.pages[0]
          self.is_uniform = False
          return [TiffPageSeries([page], page.shape, dtype, page.axes,
                                 transform=transform, kind='MDGel')]