public function resize($width = false, $height = false)
    {
        if (!$width && !$height) {
            throw new \Exception('Please, provide at least $width or $height for resize');
        }
        $result = clone $this;
        $result->operations[]['resize'] = array(
            'width' => $width,
            'height' => $height,
        );
        return $result;
    }