opencvRos1.py

#!/usr/bin/env python3

import rospy
import cv2
import sys
from cv_bridge import CvBridge, CvBridgeError
from std_msgs.msg import String
from sensor_msgs.msg import Image

bridge = CvBridge()

def image_callback(ros_image):
    print("Got an image...")
    global bridge
    # convert ros_image to opencv-compatible image
    try:
        cv_image = bridge.imgmsg_to_cv2(ros_image,"bgr8")
    except CvBridgeError as e:
        print(e)
    # when we convert the image it's all same as opencv
    (rows,cols,channels) = cv_image.shape
    if cols > 200 and rows > 200:
        cv2.circle(cv_image,(100,100),90,255)
    font = cv2.FONT_HERSHEY_SIMPLEX
    cv2.putText(cv_image,"Webcam activated with ROS & OpenCV", (10,350),font,1,(255,255,255),2,cv2.LINE_AA)
    cv2.imshow("Image Window",cv_image)
    cv2.waitKey(0)

def main(args):
  rospy.init_node('image_converter', anonymous=True)
  #for turtlebot3 waffle
  #image_topic="/camera/rgb/image_raw/compressed"
  #for usb cam
  #image_topic = "/usb_cam/image_raw"
  image_sub = rospy.Subscriber("/usb_cam/image_raw",Image, image_callback)
  try:
    rospy.spin()
  except KeyboardInterrupt:
    print("Shutting down")
  cv2.destroyAllWindows()

if __name__ == '__main__':
    main(sys.argv)