docs: def is_uniform(self):
          """Return if file contains a uniform series of pages."""
          # the hashes of IFDs 0, 7, and -1 are the same
          pages = self.pages
          page = pages[0]
          if page.is_scanimage or page.is_nih:
              return True
          try:
              useframes = pages.useframes
              pages.useframes = False
              h = page.hash
              for i in (1, 7, -1):
                  if pages[i].aspage().hash != h:
                      return False
          except IndexError:
              return False
          finally:
              pages.useframes = useframes
          return True