Hi,
I am doing Exercise: load_image2.py of OPenCV of Robotics. I think this is a problem about python itself:
when I do image-read in call_back() of topic '/camera/rgb/image_raw', and directly input msg into self.cv_bridge.imgmsg_to_cv2(), everything is alright. The code is:
#! /usr/bin/env python
import rospy
import cv2
import os
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError
class ROS_CV2_Image_Class():
def __init__(self):
# define subscriber of topic '/camera/rgb/image_raw'
self.camera_sub = rospy.Subscriber(
'/camera/rgb/image_raw', Image, self.camera_callback)
self.img = Image()
# define cv_bridge instance
self.cv_bridge = CvBridge()
# other things
self.rate = rospy.Rate(1)
self.count = 1
def camera_callback(self, msg):
self.img = msg
# get image from drone and save it
rospy.loginfo('showing ' + str(self.count) +
'th image from the drone......')
# convert camera data into array
try:
image_from_drone = self.cv_bridge.imgmsg_to_cv2(
self.img, desired_encoding="bgr8")
except CvBridgeError as e:
print(e)
cv2.imshow('the image from the drone', image_from_drone)
self.rate.sleep()
self.count += 1
# cv2.waitKey(i) functions as:
# similar with time.sleep(i)
cv2.waitKey(1)
def main(self):
try:
rospy.spin()
except KeyboardInterrupt:
print("Shutting down")
cv2.destroyAllWindows()
if __name__ == '__main__':
rospy.init_node("load_image_2_node")
ROS_cv2_image = ROS_CV2_Image_Class()
ROS_cv2_image.main()
But when I only do self.img = msg in call_back() of topic '/camera/rgb/image_raw', and do self.cv_bridge.imgmsg_to_cv2() in main(), it shows error all the time. The code is:
#! /usr/bin/env python
import rospy
import cv2
import os
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError
class ROS_CV2_Image_Class():
def __init__(self):
# define subscriber of topic '/camera/rgb/image_raw'
self.camera_sub = rospy.Subscriber(
'/camera/rgb/image_raw', Image, self.camera_callback)
self.img = Image()
# define cv_bridge instance
self.cv_bridge = CvBridge()
# other things
self.rate = rospy.Rate(1)
self.count = 1
def camera_callback(self, msg):
self.img = msg
def main(self):
# get image from drone and save it
rospy.loginfo('showing ' + str(self.count) +
'th image from the drone......')
# convert camera data into array
try:
image_from_drone = self.cv_bridge.imgmsg_to_cv2(
self.img, desired_encoding="bgr8")
except CvBridgeError as e:
print(e)
cv2.imshow('the image from the drone', image_from_drone)
self.rate.sleep()
self.count += 1
# cv2.waitKey(i) functions as:
# similar with time.sleep(i)
cv2.waitKey(1)
try:
rospy.spin()
except KeyboardInterrupt:
print("Shutting down")
cv2.destroyAllWindows()
if __name__ == '__main__':
rospy.init_node("load_image_2_node")
ROS_cv2_image = ROS_CV2_Image_Class()
ROS_cv2_image.main()
the error shows:
Unrecognized image encoding []
Traceback (most recent call last):
File "/home/user/catkin_ws/src/unit2/src/load_image_2.py", line 81, in <module>
ROS_cv2_image.main()
File "/home/user/catkin_ws/src/unit2/src/load_image_2.py", line 61, in main
cv2.imshow('the image from the drone', image_from_drone)
UnboundLocalError: local variable 'image_from_drone' referenced before assignment
[load_image_2_node-1] process has died [pid 4859, exit code 1, cmd /home/user/catkin_ws/src/unit2/src/load_image_2.py __name:=load_image_2_node __log:=/home/user/.ros/log/a302951c-6a6d-11ed-bfca-0242ac120007/load_image_2_node-1.log].
log file: /home/user/.ros/log/a302951c-6a6d-11ed-bfca-0242ac120007/load_image_2_node-1*.log
Do these 2 ways really have differences?