'Add a pixel to the region'

def add(self, x, y):

    self._pixels.append((x, y))
    self.area += 1
    self._min_x = min(self._min_x, x)
    self._max_x = max(self._max_x, x)
    self._min_y = min(self._min_y, y)
    self._max_y = max(self._max_y, y)
