How to convert ImageConstPtr to c++ string

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Hi ,

I want to convert ImageConstPtr type msg to c++ string so that same can be converted in to byte array (vector <unsigned char>). can anybody suggest any approach for the same?

below is callback for ros image subscriber where publish image is handled.

 void imageCb(const sensor_msgs::ImageConstPtr& msg)
{

//conversion of ImageConstPtr  msg type in string
string img_string = API to convert   sensor_msgs::ImageConstPtr& in to c++ string type;
vector <unsigned char> vec(img_string.begin().img_string.end());


}

is there anyway to convert cv_ImagePtr to string type?

In below code snippet cv_ptr->image will specify the image which is populated from toCvCopy API.

now i want to convert cv_ptr->image into c++ string so that i can sore the same in vector in form of unsigned char.

void imageCb(const sensor_msgs::ImageConstPtr& msg)
{
    cv_bridge::CvImagePtr cv_ptr;
    try
    {
      cv_ptr = cv_bridge::toCvCopy(msg, enc::BGR8);
    }
    catch (cv_bridge::Exception& e)
    {
      ROS_ERROR("cv_bridge exception: %s", e.what());
      return;
    }

    if (cv_ptr->image.rows > 60 && cv_ptr->image.cols > 60)
      cv::circle(cv_ptr->image, cv::Point(50, 50), 10, CV_RGB(255,0,0));

    cv::imshow(WINDOW, cv_ptr->image);
    cv::waitKey(3);
}