参考：
automaticaddison.com/getting-started-with-opencv-in-ros-2-galactic-python/
automaticaddison.com/getting-started-with-opencv-in-ros-2-foxy-fitzroy-python/推荐使用：YOLOX + ROS2 object detection package
也可以参考：github.com/jeffreyttc/opencv_ros2
vision_opencv
ros2 vision_opencv 包含将 ROS 2 与 OpenCV 接口的包，OpenCV 是一个专为计算效率和实时计算机视觉应用程序而设计的库。 该存储库包含：
- cv_bridge：ROS 2 图像消息和 OpenCV 图像表示之间的桥梁
- image_geometry：处理图像和像素几何的方法集合
- opencv_tests：集成测试以使用带有 opencv 的包的功能
- vision_opencv：安装 cv_bridge 和 image_geometry 的元包
为了将 ROS 2 与 OpenCV 一起使用，请参阅 cv_bridge 包中的详细信息。
程序适用于foxy/galactic/humble，windows/linux系统通用?
在本教程中，将学习如何将 ROS 2 与流行的计算机视觉库 OpenCV 接口的基础知识。 这些基础知识将提供在机器人应用程序中添加视觉的基础。
我们将创建一个图像发布者节点以将网络摄像头数据（即视频帧）发布到一个主题，我们将创建一个订阅该主题的图像订阅者节点。
pub发布：
| foxy | galactic |
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sub订阅：
| foxy | galactic |
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humble：
pub
# Basic ROS 2 program to publish real-time streaming
# video from your built-in webcam
# Author:
# - Addison Sears-Collins
???
# Import the necessary libraries
import rclpy # Python Client Library for ROS 2
from rclpy.node import Node # Handles the creation of nodes
from sensor_msgs.msg import Image # Image is the message type
from cv_bridge import CvBridge # Package to convert between ROS and OpenCV Images
import cv2 # OpenCV library
??
class ImagePublisher(Node):
??"""
??Create an ImagePublisher class, which is a subclass of the Node class.
??"""
??def __init__(self):
????"""
????Class constructor to set up the node
????"""
????# Initiate the Node class's constructor and give it a name
????super().__init__('image_publisher')
???????
????# Create the publisher. This publisher will publish an Image
????# to the video_frames topic. The queue size is 10 messages.
????self.publisher_ = self.create_publisher(Image, 'video_frames', 10)
???????
????# We will publish a message every 0.1 seconds
????timer_period = 0.1? # seconds
???????
????# Create the timer
????self.timer = self.create_timer(timer_period, self.timer_callback)
??????????
????# Create a VideoCapture object
????# The argument '0' gets the default webcam.
????self.cap = cv2.VideoCapture(0)
??????????
????# Used to convert between ROS and OpenCV images
????self.br = CvBridge()
????
??def timer_callback(self):
????"""
????Callback function.
????This function gets called every 0.1 seconds.
????"""
????# Capture frame-by-frame
????# This method returns True/False as well
????# as the video frame.
????ret, frame = self.cap.read()
???????????
????if ret == True:
??????# Publish the image.
??????# The 'cv2_to_imgmsg' method converts an OpenCV
??????# image to a ROS 2 image message
??????self.publisher_.publish(self.br.cv2_to_imgmsg(frame))
??
????# Display the message on the console
????self.get_logger().info('Publishing video frame')
???
def main(args=None):
???
??# Initialize the rclpy library
??rclpy.init(args=args)
???
??# Create the node
??image_publisher = ImagePublisher()
???
??# Spin the node so the callback function is called.
??rclpy.spin(image_publisher)
???
??# Destroy the node explicitly
??# (optional - otherwise it will be done automatically
??# when the garbage collector destroys the node object)
??image_publisher.destroy_node()
???
??# Shutdown the ROS client library for Python
??rclpy.shutdown()
???
if __name__ == '__main__':
??main()?sub
# Basic ROS 2 program to subscribe to real-time streaming
# video from your built-in webcam
# Author:
# - Addison Sears-Collins
???
# Import the necessary libraries
import rclpy # Python library for ROS 2
from rclpy.node import Node # Handles the creation of nodes
from sensor_msgs.msg import Image # Image is the message type
from cv_bridge import CvBridge # Package to convert between ROS and OpenCV Images
import cv2 # OpenCV library
??
class ImageSubscriber(Node):
??"""
??Create an ImageSubscriber class, which is a subclass of the Node class.
??"""
??def __init__(self):
????"""
????Class constructor to set up the node
????"""
????# Initiate the Node class's constructor and give it a name
????super().__init__('image_subscriber')
???????
????# Create the subscriber. This subscriber will receive an Image
????# from the video_frames topic. The queue size is 10 messages.
????self.subscription = self.create_subscription(
??????Image,
??????'video_frames',
??????self.listener_callback,
??????10)
????self.subscription # prevent unused variable warning
???????
????# Used to convert between ROS and OpenCV images
????self.br = CvBridge()
????
??def listener_callback(self, data):
????"""
????Callback function.
????"""
????# Display the message on the console
????self.get_logger().info('Receiving video frame')
??
????# Convert ROS Image message to OpenCV image
????current_frame = self.br.imgmsg_to_cv2(data)
?????
????# Display image
????cv2.imshow("camera", current_frame)
?????
????cv2.waitKey(1)
???
def main(args=None):
???
??# Initialize the rclpy library
??rclpy.init(args=args)
???
??# Create the node
??image_subscriber = ImageSubscriber()
???
??# Spin the node so the callback function is called.
??rclpy.spin(image_subscriber)
???
??# Destroy the node explicitly
??# (optional - otherwise it will be done automatically
??# when the garbage collector destroys the node object)
??image_subscriber.destroy_node()
???
??# Shutdown the ROS client library for Python
??rclpy.shutdown()
???
if __name__ == '__main__':
??main()