subscribe to image at regular time intervals

edit

ROS indigo OpenCV

Hi, I am writing an image subscriber and i want to use this to get some 10 images and then stop and repeat this again when I call it again. For this I have written subscriber as follows,

class SubscriberImage
{
private:
    ros::NodeHandle nh;
    image_transport::Subscriber sub;
    // ...//
public:
    int perform(std::string topic)
    {
      cv::namedWindow("view");
      cv::startWindowThread();
      image_transport::ImageTransport it(nh);
      sub = it.subscribe(topic, 1, &SubscriberImage::imageCallback,this, image_transport::TransportHints("theora"));
      while(num < 10)
          ros::spinOnce();
      cv::destroyWindow("view");
      return 0;
    }

    void imageCallback(const sensor_msgs::ImageConstPtr& msg)
    {
        **/* Here I am saving 10 images to disk */** 
        try
        {
            if (num < 10 && !cv_bridge::toCvShare(msg, "bgr8")->image.empty())
            {
                cv::imshow("view", cv_bridge::toCvShare(msg, "bgr8")->image);
                cv::imwrite(name,cv_bridge::toCvShare(msg, "bgr8")->image);
            }
            else if(cv_bridge::toCvShare(msg, "bgr8")->image.empty())
            {
                ROS_INFO_STREAM("Debug: camera image is empty");
            }
            else if(num >= 10)
            {
                sub.shutdown();
            } 
        }
    }
};

I am creating an object for this class in another node and whenever I call perform(), a new subscriber object is created and in call back i save 10 images to disk. After that I am calling sub.shutdown(). Everything works as expected but one problem is I am creating a new subscriber object every time and calling shutdown() after saving 10 images. Thus creating a new subscriber object every time takes sometime. I don't this wait time.

Can this be done in a better way? Please guide me in this.

Thanks