Slow publisher with callback

edit

Hi,

I am publishing images with the usb_cam package on a PC and subscribing to them with an arm-based system, using the following code:

#include "ros/ros.h"
#include "sensor_msgs/Image.h"

class SubscribeAndPublish
{
public:
  SubscribeAndPublish()
  {
    //Topic to publish
    pub_ = n_.advertise<sensor_msgs::Image>("/filteredHW", 1);

    //Topic to subscribe
    sub_ = n_.subscribe("/usb_cam/image_raw", 1, &SubscribeAndPublish::callback, this);
  }

  void callback(const sensor_msgs::Image& input)
  {
    sensor_msgs::Image output;

    output.header = input.header;
    output.encoding = input.encoding;
    output.height = input.height;
    output.width = input.width;
    output.step = input.step;
    output.data = input.data;

    pub_.publish(output);

  }

private:
  ros::NodeHandle n_;
  ros::Publisher pub_;
  ros::Subscriber sub_;
};//End of class SubscribeAndPublish

int main(int argc, char **argv)
{
  //Initiate ROS
  ros::init(argc, argv, "subscribe_and_publish_grayScale");

  //Create an object of class SubscribeAndPublish that will take care of everything
  SubscribeAndPublish SAPObject;

  ros::spin();

  return 0;
}

I am getting a new image on /usb_cam/image_raw at 30 Hz. However, the one that is being publish on the callback (/filteredHW) ends up at 20 Hz just by subscribing and re-publishing it.

Is there a better way to do this, to have the same rate? Note that no processing has been done so far, which would slow things down ever further.

Thank you.