    CImg<T>& operator-=(const char *const expression) {
      return *this-=(+*this)._fill(expression,true,1,0,0,"operator-=",this);
    }
    CImg<T>& operator-=(const char *const expression) {
      return *this-=(+*this)._fill(expression,true,1,0,0,"operator-=",this);
    }