code: def imgmin(self):
          
          if not hasattr(self, '_imgmin'):
              imgmin = _np.min(self.images[0])
              for img in self.images:
                  imin = _np.min(img)
                  if imin > imgmin:
                      imgmin = imin
  
              self._imgmin = imgmin
          return _np.min(self.image)
docs: Lowest value of input image.