Extract images from a rosbag.

bag_to_images.py

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

# Copyright 2016 Massachusetts Institute of Technology

"""Extract images from a rosbag.
"""

import os
import argparse

import cv2

import rosbag
from sensor_msgs.msg import Image
from cv_bridge import CvBridge

def main():
    """Extract a folder of images from a rosbag.
    """
    parser = argparse.ArgumentParser(description="Extract images from a ROS bag.")
    parser.add_argument("bag_file", help="Input ROS bag.")
    parser.add_argument("output_dir", help="Output directory.")
    parser.add_argument("image_topic", help="Image topic.")

    args = parser.parse_args()

    print "Extract images from %s on topic %s into %s" % (args.bag_file,
                                                          args.image_topic, args.output_dir)

    bag = rosbag.Bag(args.bag_file, "r")
    bridge = CvBridge()
    count = 0
    for topic, msg, t in bag.read_messages(topics=[args.image_topic]):
        cv_img = bridge.imgmsg_to_cv2(msg, desired_encoding="passthrough")

        cv2.imwrite(os.path.join(args.output_dir, "frame%06i.png" % count), cv_img)
        print "Wrote image %i" % count

        count += 1

    bag.close()

    return

if __name__ == '__main__':
    main()

Thanks, it's cool!

Great. Thank you.

If you use ros-perception then just run rosrun image_view extract_images image:=<topic>. Documentation here.

When I try this out, the images are getting saved as grayscale images. Is there any way I can get rgb images?

To export RGB, change desired_encoding to "bgr8", more sophisticated example can be seen here

I had the same problem while using a Basler ace camera, even using rqt_bag didn't give colour images. If the solution above doesn't work for you take a look at this webpage for some help: http://wiki.ros.org/image_proc .
It runs a node that gives you another topic that produces colour images you can pull from.

great!! thanks!

Congrats man! It works perfectly!

Please add information or links on how to install cv_bridge and rosbag.
Thanks!

Hello @wngreene, The code is flawless. It is great if have only to extract images from a single rosbag only once, I do not have the freedom to edit the name or the starting number of my extracted images. If i run the code on multiple rosbags, it overwrites the existing/previously created image. Please share some update on how to control the naming of the frame during extracting. !
Thank you

Hello @wngreene, I have run the code and it occurs this error: TypeError: init() takes 2 positional arguments but 3 were given. Do you know how to solve this problem?
Thank you!

THX! very useful!

This method doesn't work on compressed messages. Tweaking this code with only subscriber and playing the rosbag can work

Pretty cool:)

I'm trying to import rosbag, but it can't find the module, can someone share how you installed the module?

how can i use cv_bridge in anaconda(windows 10)? i am getting error like this
ERROR: Could not find a version that satisfies the requirement cvbridge (from versions: none)
ERROR: No matching distribution found for cvbridge

Thank you for the share

@wngreene do you have a version of script for ros2 Humble? Thank you.

@monajalal If you have a script for ros2 Humble, do share it! Thank You!