Process depth image message from ROS with openCV - image

Question

so i am currently writing a python script that is supposed to receive a ros image message and then convert it to cv2 so i can do further processing. Right now the program just receives an image and then outputs it in a little window as well as saves it as a png.
Here is my code:
#! /usr/bin/python
import rospy
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError
import cv2
bridge = CvBridge()
def image_callback(msg):
print("Received an image!")
print(msg.encoding)
try:
# Convert your ROS Image message to OpenCV2
# Converting the rgb8 image of the front camera, works fine
cv2_img = bridge.imgmsg_to_cv2(msg, 'rgb8')
# Converting the depth images, does not work
#cv2_img = bridge.imgmsg_to_cv2(msg, '32FC1')
except CvBridgeError, e:
print(e)
else:
# Save your OpenCV2 image as a png
cv2.imwrite('camera_image.png', cv2_img)
cv2.imshow('pic', cv2_img)
cv2.waitKey(0)
def main():
rospy.init_node('image_listener')
#does not work:
#image_topic = "/pepper/camera/depth/image_raw"
#works fine:
image_topic = "/pepper/camera/front/image_raw"
rospy.Subscriber(image_topic, Image, image_callback)
rospy.spin()
if __name__ == '__main__':
main()
So my problem is that my code works perfectly fine if i use the data of the front camera but does not work for the depth images.
To make sure i get the correct encoding type i used the command msg.encoding which tells me the encoding type of the current ros message.
The cv2.imshow works exactly like it should for the front camera pictures and it shows me the same as i would get if i used ros image_view but as soon as i try it with the depth image i just get a fully black or white picture unlike what image_view shows me
Here the depth image i get when i use image_view
Here the depth image i receive when i use the script and cv2.imshow
Does anyone have experience working on depth images with cv2 and can help me to get it working with the depth images as well?
I really would appreciate any help :)
Best regards

Answer 1

You could try in the following way to acquire the depth images,
import rospy
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image
import numpy as np
import cv2
def convert_depth_image(ros_image):
cv_bridge = CvBridge()
try:
depth_image = cv_bridge.imgmsg_to_cv2(ros_image, desired_encoding='passthrough')
except CvBridgeError, e:
print e
depth_array = np.array(depth_image, dtype=np.float32)
np.save("depth_img.npy", depth_array)
rospy.loginfo(depth_array)
#To save image as png
# Apply colormap on depth image (image must be converted to 8-bit per pixel first)
depth_colormap = cv2.applyColorMap(cv2.convertScaleAbs(depth_image, alpha=0.03), cv2.COLORMAP_JET)
cv2.imwrite("depth_img.png", depth_colormap)
#Or you use
# depth_array = depth_array.astype(np.uint16)
# cv2.imwrite("depth_img.png", depth_array)
def pixel2depth():
rospy.init_node('pixel2depth',anonymous=True)
rospy.Subscriber("/pepper/camera/depth/image_raw", Image,callback=convert_depth_image, queue_size=1)
rospy.spin()
if __name__ == '__main__':
pixel2depth()