public function scale($ratio)
    {
        $_width = (int)$this->do_getWidth();
        $_height = (int)$this->do_getHeight();

        if ($ratio === 1) {
            return $this;
        }

        $width = (int)($_width * $ratio);
        $height = (int)($_height * $ratio);

        $this->do_resize($width, $height);

        return $this;
    }