rosbag解出image，不用回放，python版本

#!/usr/bin/python
# -*- coding:utf-8 -*-

import roslib
import rosbag
import rospy
import cv2
from sensor_msgs.msg import Image
from cv_bridge import CvBridge
from cv_bridge import CvBridgeError
import math

class ImageCreator():
    def __init__(self):
        self.bridge = CvBridge()
        with rosbag.Bag('/home/dell/rosbag_20191028/all/2019-10-28-14-20-33_0.bag', 'r') as bag:  #要讀取的bag檔案；
            for topic,msg,t in bag.read_messages():
                if topic == "/usb_cam/image_raw": #圖像的topic；
                        try:
                            cv_image = self.bridge.imgmsg_to_cv2(msg,"bgr8")
                        except CvBridgeError as e:
                            print e
                        timestr = str(int(msg.header.stamp.to_sec()* math.pow(10,9)))# 去掉小數點
                        image_name = timestr+ ".jpg" #圖像命名：時間戳.jpg
                        cv2.imwrite(image_name, cv_image)  #儲存；

if __name__ == '__main__':

    try:
        image_creator = ImageCreator()
    except rospy.ROSInterruptException:
        pass