Dear all,

I have a problem with the following code. In particular, I would like to have a node made by a simple publisher/subscriber in order to read images, do some processing and publish an output.

image_pub = rospy.Publisher("/mycode/outputImage", Image, queue_size=1)

def main():
   rospy.init_node('node', anonymous=True)
   print('Subscribed. Waiting for images.')
   rospy.Subscriber("/usb_cam/image_raw", Image, image_callback, None, queue_size=1)
   rospy.spin()

def image_callback(msg):
   cv2_img = bridge.imgmsg_to_cv2(msg, "bgr8")
   time.sleep(1)
   image_pub.publish(bridge.cv2_to_imgmsg(cv2_img, "bgr8"))

In the node that I created to visualize the output (but also if I publish other message made by simple vectors, I see a continuous delay of around 10 seconds, instead of a static delay of 1 second as I was expecting. Moreover, it seems that it is not throwing frames and process the last one, but all the frames that are being processed are the old one captured. If I remove the sleep(1), I get a correct streaming effect. Is this a normal effect? In case it is, since my goal is to do some processing expected to run at 4/5 fps without ROS, how can I do in order to process the last frame grabbed instead of these very old frames?

Thank you