code: def imgmax(self):
          
          if not hasattr(self, '_imgmax'):
              imgmax = _np.max(self.images[0])
              for img in self.images:
                  imax = _np.max(img)
                  if imax > imgmax:
                      imgmax = imax
  
              self._imgmax = imgmax
  
          return self._imgmax
docs: Highest value of input image.