ROS中如何订阅和发布图片

Question

我正在尝试订阅“/camera/image_color”主题，该主题是我相机的数据。然后我想在 opencv 中对这些图像做一些巫术，并以特定的频率发布它们。这样我就可以用另一个节点订阅它们。

到目前为止，我已经尝试了以下代码及其许多变体。此时代码什么都不做。没有图像被发布到“/imagetimer”主题。我得到一个输出 "Timing images" 然后没有进一步发生。

#!/usr/bin/env python
# -*- encoding: utf-8 -*-
import rospy
from sensor_msgs.msg import Image
from cv_bridge import CvBridge
import cv2
import os
import numpy as np


class Nodo(object):
    def __init__(self):
        # Params
        self.image = None
        self.br = CvBridge()
        # Node cycle rate (in Hz).
        self.loop_rate = rospy.Rate(1)

        # Publishers
        self.pub = rospy.Publisher('imagetimer', Image,queue_size=10)

        # Subscribers
        rospy.Subscriber("/camera/image_color",Image,self.callback)


    def callback(self, msg):
        self.image = self.br.imgmsg_to_cv2(msg)


    def start(self):
        rospy.loginfo("Timing images")
        rospy.spin()
        br = CvBridge()
        while not rospy.is_shutdown():
            rospy.loginfo('publishing image')
            #br = CvBridge()
            self.pub.publish(br.cv2_to_imgmsg(self.image))
            rate.sleep()

if __name__ == '__main__':
    rospy.init_node("imagetimer111", anonymous=True)
    my_node = Nodo()
    my_node.start()

Answer 1

在我的例子中，我发现图像主题有压缩图像。请验证您是否属于这种情况。

我使用以下代码读取 .bag 文件。如果您发现您的 ROS 主题中有压缩图像，您可以使用此代码的部分内容来执行转换

        bag = rosbag.Bag(os.path.join(path_to_bags, bag_list[index]))
        for topic, msg, t in bag.read_messages(topics=['/conti115/image_raw/compressed']):
            try:
                img = bridge.compressed_imgmsg_to_cv2(msg)
            except CvBridgeError, e:
                print e
            txt = str(datetime.datetime.fromtimestamp(t.to_sec()))
            cv2.rectangle(img, (0, 0), (500, 40), (0,0,0), -1)
            cv2.putText(img, txt, (0, 30), 1, 2, (255, 255, 255), 2)
            cv2.imshow("win",img)


            wtr.write(img)
            if cv2.waitKey(5)==27:
                cv2.destroyAllWindows()
                break
        bag.close()

Answer 2

一旦你运行 rospy.spin() 代码就不会继续。在 rospy 中，一旦你有了 rospy.Subsriber() 行，它就会为回调分离另一个线程。 rospy.spin() 本质上使节点保持活动状态，因此回调并保持运转。此处您使用 while 循环来保持节点活动，因此不需要 rospy.spin()。这个版本应该可以工作：

import rospy
from sensor_msgs.msg import Image
from cv_bridge import CvBridge
import cv2
import os
import numpy as np

class Nodo(object):
    def __init__(self):
        # Params
        self.image = None
        self.br = CvBridge()
        # Node cycle rate (in Hz).
        self.loop_rate = rospy.Rate(1)

        # Publishers
        self.pub = rospy.Publisher('imagetimer', Image,queue_size=10)

        # Subscribers
        rospy.Subscriber("/camera/image_color",Image,self.callback)

    def callback(self, msg):
        rospy.loginfo('Image received...')
        self.image = self.br.imgmsg_to_cv2(msg)


    def start(self):
        rospy.loginfo("Timing images")
        #rospy.spin()
        while not rospy.is_shutdown():
            rospy.loginfo('publishing image')
            #br = CvBridge()
            if self.image is not None:
                self.pub.publish(br.cv2_to_imgmsg(self.image))
            self.loop_rate.sleep()

if __name__ == '__main__':
    rospy.init_node("imagetimer111", anonymous=True)
    my_node = Nodo()
    my_node.start()

ROS中如何订阅和发布图片

How to subscribe and publish images in ROS

python

opencv

ros