I’m currently using Ubuntu 20.04, ROS2-foxy
what I’m trying to do is publish webcam image with using cv2, cv_bridge and subscribe it.
I successfully publish and subscribe the webcam but not in real-time.
publish node is publishing webcam every two seconds. which means publishing image like delayed image.
I tried to search and fix the problem but and can’t make it so I need some help.
I will post my publisher and subscriber code down here.
This is publisher code.
#include <chrono>
#include <memory>
#include "cv_bridge/cv_bridge.h"
#include "rclcpp/rclcpp.hpp"
#include "sensor_msgs/msg/image.hpp"
#include "std_msgs/msg/header.hpp"
#include <opencv2/opencv.hpp>
#include <stdio.h>
#include <opencv2/core/types.hpp>
#include <opencv2/core/hal/interface.h>
#include <image_transport/image_transport.hpp>
#include <opencv2/imgproc/imgproc.hpp>
using namespace std::chrono_literals;
using namespace cv;
class MinimalPublisher : public rclcpp::Node {
public:
MinimalPublisher() : Node("minimal_publisher"), count_(0) {
auto qos_profile = rclcpp::QoS(rclcpp::KeepLast(10));
publisher_ = this->create_publisher<sensor_msgs::msg::Image>("topic", qos_profile);
timer_ = this->create_wall_timer(10ms, std::bind(&MinimalPublisher::timer_callback, this));
}
private:
void timer_callback() {
cv_bridge::CvImagePtr cv_ptr;
cv::VideoCapture cap(0);
cv::Mat img(cv::Size(1280, 720), CV_8UC3);
cap >> img;
sensor_msgs::msg::Image::SharedPtr msg = cv_bridge::CvImage(std_msgs::msg::Header(), "bgr8", img).toImageMsg();
publisher_->publish(*msg);
RCLCPP_INFO(this->get_logger(), "publishing");
}
rclcpp::TimerBase::SharedPtr timer_;
rclcpp::Publisher<sensor_msgs::msg::Image>::SharedPtr publisher_;
size_t count_;
};
int main(int argc, char *argv[]) {
printf("Starting...");
rclcpp::init(argc, argv);
rclcpp::spin(std::make_shared<MinimalPublisher>());
rclcpp::shutdown();
return 0;
}
Subscriber code:
#include <chrono>
#include <memory>
#include "cv_bridge/cv_bridge.h"
#include "rclcpp/rclcpp.hpp"
#include "sensor_msgs/msg/image.hpp"
#include "std_msgs/msg/header.hpp"
#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>
#include <stdio.h>
#include <opencv2/core/types.hpp>
#include <opencv2/core/hal/interface.h>
#include <image_transport/image_transport.hpp>
#include <opencv2/imgproc/imgproc.hpp>
using std::placeholders::_1;
class MinimalSubscriber : public rclcpp::Node {
public:
MinimalSubscriber()
: Node("minimal_subscriber")
{
auto qos_profile = rclcpp::QoS(rclcpp::KeepLast(10));
subscription_ = this->create_subscription<sensor_msgs::msg::Image>(
"topic", qos_profile, std::bind(&MinimalSubscriber::topic_callback, this, _1));
}
private :
void topic_callback(sensor_msgs::msg::Image::SharedPtr msg) const
{
RCLCPP_INFO(this->get_logger(), "In callback");
cv_bridge::CvImagePtr cv_ptr;
cv_ptr = cv_bridge::toCvCopy(msg,"bgr8");
cv::imshow("minimal_subscriber", cv_ptr->image);
cv::waitKey(1);
}
rclcpp::Subscription<sensor_msgs::msg::Image>::SharedPtr subscription_;
};
int main(int argc, char *argv[])
{
rclcpp::init(argc, argv);
rclcpp::spin(std::make_shared<MinimalSubscriber>());
rclcpp::shutdown();
return 0;
}
I want to see my webcam streaming working normally. I want this simple job happen in C++, cv_bridge, cv2.
2
Answers
Every time the timer_callback function is called, you’re opening a new video capture stream with cv::VideoCapture cap(0);. The opening and closing of the video stream is be causing the delay you’re experiencing.
Fixed it !
here is a detailed code : https://github.com/Robotisim/solving_ros_problems/commit/b099e5d787d91205225416953516813ba2dce7c3
Hello I could not fix the same problem,
I run your code @Muhammad Luqman but shows the following errors
Starting…[ WARN:0] global ./modules/videoio/src/cap_gstreamer.cpp (2075) handleMessage OpenCV | GStreamer warning: Embedded video playback halted; module v4l2src0 reported: Cannot identify device ‘/dev/video0’.
[ WARN:0] global ./modules/videoio/src/cap_gstreamer.cpp (1053) open OpenCV | GStreamer warning: unable to start pipeline
[ WARN:0] global ./modules/videoio/src/cap_gstreamer.cpp (616) isPipelinePlaying OpenCV | GStreamer warning: GStreamer: pipeline have not been created
[ WARN:0] global ./modules/videoio/src/cap_v4l.cpp (890) open VIDEOIO(V4L2:/dev/video0): can’t open camera by index
//Please Help. I am using ubuntu 22.04 on windows