lag in image saving / subscribing

edit

Hey guys. I am having troblues in saving the last image from bebeop 2 parrot drone on my laptop. I run ROS Kinetic, Ubuntu 16.04 OS and use bebeop_autonomy driver.

In the following code I wish to save an Image only after the camera completes the action of moving the camera down.

#!/usr/bin/env python
from __future__ import print_function
import sys
import rospy
import cv2
import numpy as np
import time
from geometry_msgs.msg import Twist
from std_msgs.msg import Empty
from std_msgs.msg import Int16  # For error/angle plot publishing
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError

class image_converter:

def __init__(self):
    self.bridge = CvBridge()
    self.pub_camdown = rospy.Publisher('/bebop/camera_control', Twist, queue_size=1)
    self.image_sub = rospy.Subscriber('/bebop/image_raw', Image, self.callback)

def cam_down(self):
    cam = Twist()
    cam.angular.y = -50.0
    self.pub_camdown.publish(cam)

def callback(self, msg):
    rospy.sleep(1)
    try:
        # Convert your ROS Image message to OpenCV2
        cv2_img = self.bridge.imgmsg_to_cv2(msg, "bgr8")  # cv2_img = CvBridge.imgmsg_to_cv2(msg, "bgr8")
    except CvBridgeError, e:
        print(e)
    else:
        time = msg.header.stamp
        saved_img = cv2.imwrite(''+str(time)+'.jpeg', cv2_img)
        cv2.imshow("Image window", cv2_img)
        cv2.waitKey(1000)


def main(args):
rospy.init_node('image_converter', anonymous=True)
ic = image_converter()
time.sleep(1)
ic.cam_down()
try:
    rospy.spin()
except KeyboardInterrupt:
    print("Shutting down")
    cv2.destroyAllWindows()


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

The callback function runs 10 times before saving the required images (the image after moving down the camera) Any ideas that can fix it?

Changes I tried that did not work:

1. setting Queue_size=1 or Queue_size=10 to the line of subscribing the image,
2. using different times in rospy.sleep(1) in the callback function results in the same number of iterations before getting the wanted image.
3. using different times in time.sleep(1) in the main function results the same.