Unable to publish an image using cvbridge [closed]

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Hello,

I am trying to create a simple image publisher from OpenCV to ROS, I am following the given tutorial. http://wiki.ros.org/cv_bridge/Tutoria...

However, when I run the program I get the following error:

ROS distribution: Kinetic Kame OpenCV: 3.4.0

Traceback (most recent call last):

File "/home/deepak/catkin_ws/src/python_learning/src/scripts/image_pub.py", line 40, in <module> main() File "/home/deepak/catkin_ws/src/python_learning/src/scripts/image_pub.py", line 36, in main image_publisher_obj.img_pub_node() File "/home/deepak/catkin_ws/src/python_learning/src/scripts image_pub.py", line 24, in img_pub_node ros_img = self.cvbridge_obj.cv2_to_imgmsg(cv_img, encoding="bgr8")    File "/opt/ros/kinetic/lib/python2.7/dist-packages/cv_bridge/core.py", line 246, in cv2_to_imgmsg raise TypeError('Your input type is not a numpy array') TypeError: Your input type is not a numpy array

My code is:

class ImagePublisher:
""" Class to define member functions for image publisher """

def __init__(self):
    """ Constructor """
    self.image_pub = rospy.Publisher("image_pub_topic", img,queue_size=200)
    self.cvbridge_obj = CvBridge()

def img_pub_node(self):
    """ Publisher helper function """
    cv_img = cv2.imread('sizeDetect.jpg')

    # Convert this to ROS image format
    ros_img = self.cvbridge_obj.cv2_to_imgmsg(cv_img, encoding="bgr8")
    try:
        self.image_pub.publish(ros_img)
        rate = rospy.Rate(10)
        rate.sleep()
    except CvBridgeError as bridgerr:
        print(bridgerr)

def main():
    "Main function"
    image_publisher_obj = ImagePublisher()
    rospy.init_node('img_pub_node', anonymous=True)
    image_publisher_obj.img_pub_node()
    rospy.spin()

if __name__ == '__main__':
    main()

My understanding is that OpenCV in Python will return numpy array and C++ will return Mat class. Then why is he complaining that it is not a numpy array.