protected function randomColor($image)
    {
        if($this->ismono) {
            return imagecolorallocatealpha($image, $this->monocolor[0], $this->monocolor[1], $this->monocolor[2], $this->rand(0, 96));
        }
        return imagecolorallocate($image, $this->rand(0, 255), $this->rand(0, 255), $this->rand(0, 255));
    }