I have a workstation running Python2 with a ROS environment which obtains a camera image from a robot and sends it over the network to a Python3 machine using the standard socket library. I can't seem to unpickle correctly the opencv ndarray image.
I am able to successfully transfer simple data as lists, but I encounter an error when trying to transfer an image.
On the Python2 system, I obtain my image in this way:
img = CvBridge().imgmsg_to_cv2(img_data, desired_encoding='bgr8') # Convert from ROS image to OpenCV image
Obtaining an ndarray. I serialize it with:
data = pickle.dumps(img, protocol=0)
And I send it. Back on the Python3 machine, I try to unpickle it using:
response = pickle.loads(data_in, encoding='latin1') # To read a Python2 dump
At this point, I obtain the following error:
_pickle.UnpicklingError: the STRING opcode argument must be quoted
The only other solutions that I have found address cases in which data had been transferred between Unix and Windows machines, which is not my case.
An update on this topic, for possible future reference to whoever will experience the same problem.
The problem was not caused, as I initially thought, by a misconversion between Py2 and Py3 pickled byte stream. It was caused, instead, by the incorrect transmission of the data: I was interrupting the connection before all the packages had arrived. This is the block of code that solved my problem:
data_in = b''
while True:
block = self.socket.recv(4096)
if block:
data_in += block