text: #! /usr/bin/env python3
  
  import rospy
  import cv2
  
  from sensor_msgs.msg import Image
  
  from cv_bridge import CvBridge
  
  
  global bridge
  bridge = CvBridge()
  
  def callback(data):
      
      cv_image =  bridge.imgmsg_to_cv2(data, 'bgr8')
      cv2.imshow('callback',cv_image)
      cv2.waitKey(1)
      pass
  def main():
      rospy.init_node('img_opencv')
      rospy.Subscriber('/usb_cam/image_raw',Image,callback)
      rospy.spin()
      
  
  if __name__ =='__main__':
  
      main()
      pass