Subscribing to a ROS sensor_msg/Image using python

Question

I'm trying to subscribe to a ROS node published by a vrep vision sensor. Here is my code, which works fine when using my built-in webcam:

import rospy
from sensor_msgs.msg import Image
from std_msgs.msg import String
from cv_bridge import CvBridge, CvBridgeError
import cv2
import numpy as np
import tensorflow as tf
import classify_image


class RosTensorFlow():
def __init__(self):
    classify_image.maybe_download_and_extract()
    self._session = tf.Session()
    classify_image.create_graph()
    self._cv_bridge = CvBridge()

    self._sub = rospy.Subscriber('image', Image, self.callback, queue_size=1)
    self._pub = rospy.Publisher('result', String, queue_size=1)
    self.score_threshold = rospy.get_param('~score_threshold', 0.1)
    self.use_top_k = rospy.get_param('~use_top_k', 5)

def callback(self, image_msg):
try:
        cv_image = self._cv_bridge.imgmsg_to_cv2(image_msg, desired_encoding="passthrough")
except CvBridgeError as e:
    print(e)

    # copy from
    # classify_image.py
    image_data = cv2.imencode('.jpg', cv_image)[1].tostring()
    # Creates graph from saved GraphDef.
    softmax_tensor = self._session.graph.get_tensor_by_name('softmax:0')
    predictions = self._session.run(
        softmax_tensor, {'DecodeJpeg/contents:0': image_data})
    predictions = np.squeeze(predictions)
    # Creates node ID --> English string lookup.
    node_lookup = classify_image.NodeLookup()
    top_k = predictions.argsort()[-self.use_top_k:][::-1]
    for node_id in top_k:
        human_string = node_lookup.id_to_string(node_id)
        score = predictions[node_id]
        if score > self.score_threshold:
            rospy.loginfo('%s (score = %.5f)' % (human_string, score))
            self._pub.publish(human_string)

def main(self):
    rospy.spin()

if __name__ == '__main__':
  classify_image.setup_args()
  rospy.init_node('rostensorflow')
  tensor = RosTensorFlow()
  tensor.main()

and my non-threaded child-script in vrep, which i basically copied from the rosInterfaceTopicPublisherAndSubscriber.ttt tutorial:

function sysCall_init()

  activeVisionSensor=sim.getObjectHandle('Vision_sensor')

  pub=simROS.advertise('image', 'sensor_msgs/Image')
  simROS.publisherTreatUInt8ArrayAsString(pub) -- treat uint8 arrays as strings (much faster, tables/arrays are kind of slow in Lua)
end



function sysCall_sensing()
  -- Publish the image of the active vision sensor:
  local data,w,h=sim.getVisionSensorCharImage(activeVisionSensor)
  d={}
  d['header']={seq=0,stamp=simROS.getTime(), frame_id="a"}
  d['height']=h
  d['width']=w
  d['encoding']='rgb8'
  d['is_bigendian']=1
  d['step']=w*3
  d['data']=data
  simROS.publish(pub,d)
  print("published")
end

function sysCall_cleanup()
  simROS.shutdownPublisher(pub)
end

I'm running the script with:

python image_recognition.py

I'm getting no error message, but there is just no output. Can you please give me a hint what I need to change? I did a lot of research but without any success so far.

Answer 1

Got it working. For people interested, I was running:

rostopic list -v

which told me that the node was actually published as:

/vrep_ros_interface/image

I just changed that in

rospy.Subscriber

and the script worked :)