public function size($int_width, $int_height)
    {
        if (!is_integer($int_width) || !is_integer($int_height) || $int_width < 0 || $int_height < 0) {
            throw new \InvalidArgumentException('Width and height must be positive integers!');
        }

        $this->size->w = $int_width;
        $this->size->h = $int_height;

        return $this;
    }