how to recover the saved images in a bagfile to jpg or png

edit

I use the Python script below as a ROS node to convert a bag file to a set of images in a directory. To run I use:

rosrun my_package bag_to_images.py ../saved_images ../input.bag

where the saved_images/ directory must exist beforehand. Also, give the location of saved_images/ relative to the directory where the bag_to_images.py script is located. The input.bag file should also be specified relative to the directory where the bag_to_images.py script is located. It is possible to use this in a launch file but I never do that.

For each image topic just put another if topic == section into the script and modify the topic names to match those in your bag file. The images get saved to saved_images/right_{message timestamp}.pgm. To save as .png or .jpg just change those lines to use those file extensions, as OpenCV is smart enough to figure out how to write the files the correct way. See here at the cv::imread section for supported formats with OpenCV.

#!/usr/bin/python

# Start up ROS pieces.
PKG = 'my_package'
import roslib; roslib.load_manifest(PKG)
import rosbag
import rospy
import cv
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError

# Reading bag filename from command line or roslaunch parameter.
import os
import sys

class ImageCreator():
    # Must have __init__(self) function for a class, similar to a C++ class constructor.
    def __init__(self):
        # Get parameters when starting node from a launch file.
        if len(sys.argv) < 1:
            save_dir = rospy.get_param('save_dir')
            filename = rospy.get_param('filename')
            rospy.loginfo("Bag filename = %s", filename)
        # Get parameters as arguments to 'rosrun my_package bag_to_images.py <save_dir> <filename>', where save_dir and filename exist relative to this executable file.
        else:
            save_dir = os.path.join(sys.path[0], sys.argv[1])
            filename = os.path.join(sys.path[0], sys.argv[2])
            rospy.loginfo("Bag filename = %s", filename)

        # Use a CvBridge to convert ROS images to OpenCV images so they can be saved.
        self.bridge = CvBridge()

        # Open bag file.
        with rosbag.Bag(filename, 'r') as bag:
            for topic, msg, t in bag.read_messages():
                if topic == "/left/image_raw":
                    try:
                        cv_image = self.bridge.imgmsg_to_cv(msg, "bgr8")
                    except CvBridgeError, e:
                        print(e)
                    timestr = "%.6f" % msg.header.stamp.to_sec()
                    image_name = str(save_dir)+"/left_"+timestr+".pgm"
                    #image_name = str(save_dir)+"/"+timestr+"_left"+".pgm"
                    cv.SaveImage(image_name, cv_image)
                if topic == "/right/image_raw":
                    try:
                        cv_image = self.bridge.imgmsg_to_cv(msg, "bgr8")
                    except CvBridgeError, e:
                        print(e)
                    timestr = "%.6f" % msg.header.stamp.to_sec()
                    image_name = str(save_dir)+"/right_"+timestr+".pgm"
                    #image_name = str(save_dir)+"/"+timestr+"_right"+".pgm"
                    cv.SaveImage(image_name, cv_image)

# Main function.    
if __name__ == '__main__':
    # Initialize the node and name it.
    rospy.init_node(PKG)
    # Go to class functions that do all the heavy lifting. Do error checking.
    try:
        image_creator = ImageCreator()
    except rospy.ROSInterruptException: pass

I modified Thomas D's answer for OpenCV version 2.

* All topics that contain a search term (desired_topic) are accepted.
* Option to include image index with leading zeroes (index_in_filename)
* Delimiter changed to '-' to avoid confusion with underscores in topic names.
* Support for compressed topics.

Code:

#!/usr/bin/python

# Extract images from a bag file.
#
# Original author: Thomas Denewiler (http://answers.ros.org/users/304/thomas-d/)

# Start up ROS pieces.
PKG = 'my_package'
import roslib; roslib.load_manifest(PKG)
import rosbag
import rospy
import cv2
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError

# Reading bag filename from command line or roslaunch parameter.
import os
import sys

class ImageCreator():

    image_type = ".jpg"
    desired_topic = "image_raw"
    index_in_filename = True
    index_format = "06d"
    image_index = 0

    # Must have __init__(self) function for a class, similar to a C++ class constructor.
    def __init__(self):
        # Get parameters when starting node from a launch file.
        if len(sys.argv) < 1:
            save_dir = rospy.get_param('save_dir')
            filename = rospy.get_param('filename')
            rospy.loginfo("Bag filename = %s", filename)
        # Get parameters as arguments to 'rosrun my_package bag_to_images.py <save_dir> <filename>', where save_dir and filename exist relative to this executable file.
        else:
            save_dir = os.path.join(sys.path[0], sys.argv[1])
            filename = os.path.join(sys.path[0], sys.argv[2])
            rospy.loginfo("Bag filename = %s", filename)

        # Use a CvBridge to convert ROS images to OpenCV images so they can be saved.
        self.bridge = CvBridge()

        # Open bag file.
        with rosbag.Bag(filename, 'r') as bag:
            for topic, msg, t in bag.read_messages():
                topic_parts = topic.split('/')
                # first part is empty string
                if len(topic_parts) == 3 and topic_parts[2] == self.desired_topic:
                    try:
                        cv_image = self.bridge.imgmsg_to_cv2(msg, "bgr8")
                    except CvBridgeError, e:
                        print(e)
                    timestr = "%.3f" % msg.header.stamp.to_sec()
                    if self.index_in_filename:
                        image_name = str(save_dir) + "/" + topic_parts[1] + "-" + format(self.image_index, self.index_format) + "-" + timestr + self.image_type
                    else:
                        image_name = str(save_dir) + "/" + topic_parts[1] + "-" + timestr + self.image_type
                    cv2.imwrite(image_name, cv_image)
                    self.image_index = self.image_index + 1

# Main function.    
if __name__ == '__main__':
    # Initialize the node and name it.
    rospy.init_node(PKG)
    # Go to class functions that do all the heavy lifting. Do error checking.
    try:
        image_creator = ImageCreator()
    except rospy.ROSInterruptException: pass

The easiest way I found was using "image_saver" tool of "image_view" package through the terminal. More details can be found at : http://wiki.ros.org/image_view .

example: Play the *.bag file and use "rosrun image_view image_saver image:=[your topic]"

similarly "video_recorder" tool can be used for extracting video.

have you tried bag_to_pcd? then you can use pcd_viewer and take a screenshot which is saved as a png file.

http://www.ros.org/wiki/pcl_ros#bag_to_pcd

and you need to edit the code a bit but its explained here: http://www.pcl-users.org/conversion-bag-to-pcd-td2770573.html