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import rclpy
from rclpy.node import Node
from sensor_msgs.msg import Image, CompressedImage
from cv_bridge import CvBridge
import cv2

#https://docs.ros.org/en/indigo/api/cv_bridge/html/python/

class ImagePublisher(Node):

  def __init__(self):
    super().__init__('Webcam_publisher')
    self.publisher_ = self.create_publisher(CompressedImage, '/webcam/image_raw/compressed', 1)
    timer_period = 0.333
    self.timer = self.create_timer(timer_period, self.timer_callback)
    self.cap = cv2.VideoCapture(0)
    if not self.cap.isOpened():
    	print("VideoCapture error!!")
    	exit()
    self.br = CvBridge()

  def timer_callback(self):
    ret, frame = self.cap.read()
    if ret == True:
      self.publisher_.publish(self.br.cv2_to_compressed_imgmsg(frame, dst_format='jpg'))
      #self.publisher_.publish(self.br.cv2_to_compressed_imgmsg(frame, "bgr8"))
    self.get_logger().info('Publishing video frame')

def main(args=None):
  rclpy.init(args=args)
  image_publisher = ImagePublisher()
  rclpy.spin(image_publisher)
  image_publisher.destroy_node()
  rclpy.shutdown()

if __name__ == '__main__':
  main()


==========================================================================================================

import rclpy
from rclpy.node import Node
from sensor_msgs.msg import Image, CompressedImage
from cv_bridge import CvBridge
import cv2

class ImageSubscriber(Node):

  def __init__(self):
    super().__init__('Webcam_subscriber')
    self.subscription = self.create_subscription(CompressedImage, '/webcam/image_raw/compressed', self.listener_callback, 1)
    self.subscription # prevent unused variable warning
    self.br = CvBridge()

  def listener_callback(self, data):
    self.get_logger().info('Receiving video frame')
    current_frame = self.br.compressed_imgmsg_to_cv2(data)
    cv2.imshow("camera", current_frame)
    cv2.waitKey(1)

def main(args=None):
  rclpy.init(args=args)
  image_subscriber = ImageSubscriber()
  rclpy.spin(image_subscriber)
  image_subscriber.destroy_node()
  rclpy.shutdown()

if __name__ == '__main__':
  main()