image_subscriber.py

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#!/usr/bin/python
# BSD 3-Clause License

# Copyright (c) 2019, Noam C. Golombek
# All rights reserved.

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import timeit
import numpy as np
import cv2

import rospy
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image, CompressedImage

class ImageSubscriber(object):
    '''A class to subscribe to a ROS camera'''

    def __init__(self, topic="usb_cam/image_raw"):
        '''Initialize ros publisher, ros subscriber'''

        self.currentImage = None
        self.currentHeader = None
        self.compressed = True if "compressed" in topic else False
        self.frame_count = 0
        self.start_time = timeit.default_timer()

        if not self.compressed:
            self.bridge = CvBridge()
            self.subscriber = rospy.Subscriber(topic,
                                               Image, self.callback,  queue_size=1)
        else:
            self.subscriber = rospy.Subscriber(
                topic, CompressedImage, self.callback, queue_size=1)

    def callback(self, ros_data):
        '''Callback function of subscribed topic. 
        Here images get converted to cv2 format'''
        
        if not self.compressed:
            self.currentImage = cv2.resize(
                self.bridge.imgmsg_to_cv2(ros_data, "rgb8"),
                (640, 480))
        else:
            np_arr = np.fromstring(ros_data.data, np.uint8)
            image_np = cv2.imdecode(np_arr, 1)

            self.currentImage = cv2.cvtColor(image_np, cv2.COLOR_BGR2RGB)

        self.currentHeader = ros_data.header
        
        self.frame_count += 1