Python MQTT Publish JSONified Numpy Array

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I am currently implementing a MQTT protocol to be used between two raspberry pis. The first is a Pi 0 and will have a pi camera connected to it. It will be converting each captured frame to a numpy array and then publish it to the master Pi which will then convert the numpy array to an image using PIL. I am doing it this way since I want the main image processing operations to be performed on the master Pi.

My problem is that no messages are being received by the master Pi. I have preformed debugging and everything is working fine on the servant script. But for some reason nothing is received by the master Pi.

Here are both scripts:

servant.py:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

master.py:

import paho.mqtt.client as mqtt

import numpy as np

import json

import PIL



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



def on_connect(client, userdata, flags, rc):

    print("connected with result code " + str(rc))

    client.subscribe(MQTT_PATH)



def on_message(client, userdata, msg):

    data = json.loads(msg.payload)

    array = np.array(data)

    img = PIL.Image.fromarray(array)

    cv2.imshow('image', img)

    cv2.waitKey()



client = mqtt.Client()

client.on_connect = on_connect

client.on_message = on_message

client.connect(MQTT_SERVER, 1883, 60)



client.loop_forever()

edited yesterday

asked yesterday

Noor Sabbagh

New contributor

You need to explain what you have tried, just saying "I have performed debugging" doesn't help
– hardillb
yesterday

Also you are blocking in the on_message by calling cv2.waitKey() this means the whole subscriber will lock up while processing the first message until you press a key. You should not block messaging handling.
– hardillb
yesterday

1

Don't need to call mqttc.loop_start() in your client (or periodically call loop from within your for loop)?
– larsks
yesterday

@hardillb sorry i didnt specify the exact debugging techniques but i think it is redundant nonetheless because the servant script is working perfectly fine. But, to answer your question i did a few logging statements on the servant.py and the data is being processed properly and is jsonified. I also made a dummy numpy array and that actually went through and was published. But for some reason the moment i use opencv it stops working. Once again even with the opencv on the servant.py everything works fine, publishing is the problem.
– Noor Sabbagh
yesterday

@hardillb as for your suggestion I removed that line but there was still nothing showing up. Don't even think that is the problem, because i quickly debugged it using a print statement, first line in the on_message method, and the msg.payload's value is not printed. Which means that somewhere between the publish and the on_message something is going wrong.
– Noor Sabbagh
yesterday

|
show 2 more comments

up vote
0
down vote

favorite

Here are both scripts:

servant.py:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

master.py:

import paho.mqtt.client as mqtt

import numpy as np

import json

import PIL



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



def on_connect(client, userdata, flags, rc):

    print("connected with result code " + str(rc))

    client.subscribe(MQTT_PATH)



def on_message(client, userdata, msg):

    data = json.loads(msg.payload)

    array = np.array(data)

    img = PIL.Image.fromarray(array)

    cv2.imshow('image', img)

    cv2.waitKey()



client = mqtt.Client()

client.on_connect = on_connect

client.on_message = on_message

client.connect(MQTT_SERVER, 1883, 60)



client.loop_forever()

edited yesterday

asked yesterday

Noor Sabbagh

New contributor

You need to explain what you have tried, just saying "I have performed debugging" doesn't help
– hardillb
yesterday

Also you are blocking in the on_message by calling cv2.waitKey() this means the whole subscriber will lock up while processing the first message until you press a key. You should not block messaging handling.
– hardillb
yesterday

1

Don't need to call mqttc.loop_start() in your client (or periodically call loop from within your for loop)?
– larsks
yesterday

@hardillb sorry i didnt specify the exact debugging techniques but i think it is redundant nonetheless because the servant script is working perfectly fine. But, to answer your question i did a few logging statements on the servant.py and the data is being processed properly and is jsonified. I also made a dummy numpy array and that actually went through and was published. But for some reason the moment i use opencv it stops working. Once again even with the opencv on the servant.py everything works fine, publishing is the problem.
– Noor Sabbagh
yesterday

@hardillb as for your suggestion I removed that line but there was still nothing showing up. Don't even think that is the problem, because i quickly debugged it using a print statement, first line in the on_message method, and the msg.payload's value is not printed. Which means that somewhere between the publish and the on_message something is going wrong.
– Noor Sabbagh
yesterday

|
show 2 more comments

up vote
0
down vote

favorite

Here are both scripts:

servant.py:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

master.py:

import paho.mqtt.client as mqtt

import numpy as np

import json

import PIL



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



def on_connect(client, userdata, flags, rc):

    print("connected with result code " + str(rc))

    client.subscribe(MQTT_PATH)



def on_message(client, userdata, msg):

    data = json.loads(msg.payload)

    array = np.array(data)

    img = PIL.Image.fromarray(array)

    cv2.imshow('image', img)

    cv2.waitKey()



client = mqtt.Client()

client.on_connect = on_connect

client.on_message = on_message

client.connect(MQTT_SERVER, 1883, 60)



client.loop_forever()

edited yesterday

asked yesterday

Noor Sabbagh

New contributor

Here are both scripts:

servant.py:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

master.py:

import paho.mqtt.client as mqtt

import numpy as np

import json

import PIL



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



def on_connect(client, userdata, flags, rc):

    print("connected with result code " + str(rc))

    client.subscribe(MQTT_PATH)



def on_message(client, userdata, msg):

    data = json.loads(msg.payload)

    array = np.array(data)

    img = PIL.Image.fromarray(array)

    cv2.imshow('image', img)

    cv2.waitKey()



client = mqtt.Client()

client.on_connect = on_connect

client.on_message = on_message

client.connect(MQTT_SERVER, 1883, 60)



client.loop_forever()

python numpy raspberry-pi mqtt

edited yesterday

asked yesterday

Noor Sabbagh

New contributor

edited yesterday

asked yesterday

Noor Sabbagh

New contributor

edited yesterday

asked yesterday

Noor Sabbagh

New contributor

asked yesterday

Noor Sabbagh

asked yesterday

Noor Sabbagh

New contributor

Noor Sabbagh is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

You need to explain what you have tried, just saying "I have performed debugging" doesn't help
– hardillb
yesterday

Also you are blocking in the on_message by calling cv2.waitKey() this means the whole subscriber will lock up while processing the first message until you press a key. You should not block messaging handling.
– hardillb
yesterday

1

Don't need to call mqttc.loop_start() in your client (or periodically call loop from within your for loop)?
– larsks
yesterday

@hardillb sorry i didnt specify the exact debugging techniques but i think it is redundant nonetheless because the servant script is working perfectly fine. But, to answer your question i did a few logging statements on the servant.py and the data is being processed properly and is jsonified. I also made a dummy numpy array and that actually went through and was published. But for some reason the moment i use opencv it stops working. Once again even with the opencv on the servant.py everything works fine, publishing is the problem.
– Noor Sabbagh
yesterday

@hardillb as for your suggestion I removed that line but there was still nothing showing up. Don't even think that is the problem, because i quickly debugged it using a print statement, first line in the on_message method, and the msg.payload's value is not printed. Which means that somewhere between the publish and the on_message something is going wrong.
– Noor Sabbagh
yesterday

|
show 2 more comments

You need to explain what you have tried, just saying "I have performed debugging" doesn't help
– hardillb
yesterday

Also you are blocking in the on_message by calling cv2.waitKey() this means the whole subscriber will lock up while processing the first message until you press a key. You should not block messaging handling.
– hardillb
yesterday

1

Don't need to call mqttc.loop_start() in your client (or periodically call loop from within your for loop)?
– larsks
yesterday

@hardillb sorry i didnt specify the exact debugging techniques but i think it is redundant nonetheless because the servant script is working perfectly fine. But, to answer your question i did a few logging statements on the servant.py and the data is being processed properly and is jsonified. I also made a dummy numpy array and that actually went through and was published. But for some reason the moment i use opencv it stops working. Once again even with the opencv on the servant.py everything works fine, publishing is the problem.
– Noor Sabbagh
yesterday

@hardillb as for your suggestion I removed that line but there was still nothing showing up. Don't even think that is the problem, because i quickly debugged it using a print statement, first line in the on_message method, and the msg.payload's value is not printed. Which means that somewhere between the publish and the on_message something is going wrong.
– Noor Sabbagh
yesterday

You need to explain what you have tried, just saying "I have performed debugging" doesn't help
– hardillb
yesterday

Also you are blocking in the on_message by calling cv2.waitKey() this means the whole subscriber will lock up while processing the first message until you press a key. You should not block messaging handling.
– hardillb
yesterday

Don't need to call mqttc.loop_start() in your client (or periodically call loop from within your for loop)?
– larsks
yesterday

@hardillb sorry i didnt specify the exact debugging techniques but i think it is redundant nonetheless because the servant script is working perfectly fine. But, to answer your question i did a few logging statements on the servant.py and the data is being processed properly and is jsonified. I also made a dummy numpy array and that actually went through and was published. But for some reason the moment i use opencv it stops working. Once again even with the opencv on the servant.py everything works fine, publishing is the problem.
– Noor Sabbagh
yesterday

@hardillb as for your suggestion I removed that line but there was still nothing showing up. Don't even think that is the problem, because i quickly debugged it using a print statement, first line in the on_message method, and the msg.payload's value is not printed. Which means that somewhere between the publish and the on_message something is going wrong.
– Noor Sabbagh
yesterday

|
show 2 more comments

1 Answer
1

active

oldest

votes

up vote
0
down vote

accepted

In your publishing code you are not actually giving the client any time to process the message it is trying to send. This is even more of a problem because the message is likely to be larger than a single network packet (being an image). To fix this you have to call the MQTT client loop function (or start the loop in the b

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    mqttc.loop()

    time.sleep(1)

or like this:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



mqttc.start_loop()



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

answered yesterday

hardillb

23.1k63059

Thank you so much, one more question, do you think this is a good way of doing things or is there a more lightweight way of doing it? Actually in my real script im going to have the pi camera module on the servant.py instead of opencv. Is byte streaming the image to the master going to be more efficient and faster than my current way?
– Noor Sabbagh
22 hours ago

But the problem is still there. I removed the waitkey and added the loop for the client but the master is still not receiving anything.
– Noor Sabbagh
21 hours ago

add a comment |

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1 Answer
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1 Answer
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oldest

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up vote
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accepted

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    mqttc.loop()

    time.sleep(1)

or like this:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



mqttc.start_loop()



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

answered yesterday

hardillb

23.1k63059

Thank you so much, one more question, do you think this is a good way of doing things or is there a more lightweight way of doing it? Actually in my real script im going to have the pi camera module on the servant.py instead of opencv. Is byte streaming the image to the master going to be more efficient and faster than my current way?
– Noor Sabbagh
22 hours ago

But the problem is still there. I removed the waitkey and added the loop for the client but the master is still not receiving anything.
– Noor Sabbagh
21 hours ago

add a comment |

up vote
0
down vote

accepted

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    mqttc.loop()

    time.sleep(1)

or like this:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



mqttc.start_loop()



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

answered yesterday

hardillb

23.1k63059

Thank you so much, one more question, do you think this is a good way of doing things or is there a more lightweight way of doing it? Actually in my real script im going to have the pi camera module on the servant.py instead of opencv. Is byte streaming the image to the master going to be more efficient and faster than my current way?
– Noor Sabbagh
22 hours ago

But the problem is still there. I removed the waitkey and added the loop for the client but the master is still not receiving anything.
– Noor Sabbagh
21 hours ago

add a comment |

up vote
0
down vote

accepted

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    mqttc.loop()

    time.sleep(1)

or like this:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



mqttc.start_loop()



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

answered yesterday

hardillb

23.1k63059

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    mqttc.loop()

    time.sleep(1)

or like this:

import paho.mqtt.client as mqtt

import time

import cv2

import numpy

import json



MQTT_SERVER = "iot.eclipse.org"

MQTT_PATH = "test_channel"



mqttc = mqtt.Client()

mqttc.connect(MQTT_SERVER, 1883, 60)



cap = cv2.VideoCapture(0)



mqttc.start_loop()



while True:

    ret, frame = cap.read()

    frame_list = frame.tolist()

    MQTT_MESSAGE = json.dumps(frame_list)

    mqttc.publish(MQTT_PATH, MQTT_MESSAGE)

    time.sleep(1)

answered yesterday

hardillb

23.1k63059

answered yesterday

hardillb

23.1k63059

answered yesterday

hardillb

23.1k63059

answered yesterday

hardillb

23.1k63059

Thank you so much, one more question, do you think this is a good way of doing things or is there a more lightweight way of doing it? Actually in my real script im going to have the pi camera module on the servant.py instead of opencv. Is byte streaming the image to the master going to be more efficient and faster than my current way?
– Noor Sabbagh
22 hours ago

But the problem is still there. I removed the waitkey and added the loop for the client but the master is still not receiving anything.
– Noor Sabbagh
21 hours ago

add a comment |

Thank you so much, one more question, do you think this is a good way of doing things or is there a more lightweight way of doing it? Actually in my real script im going to have the pi camera module on the servant.py instead of opencv. Is byte streaming the image to the master going to be more efficient and faster than my current way?
– Noor Sabbagh
22 hours ago

But the problem is still there. I removed the waitkey and added the loop for the client but the master is still not receiving anything.
– Noor Sabbagh
21 hours ago

Thank you so much, one more question, do you think this is a good way of doing things or is there a more lightweight way of doing it? Actually in my real script im going to have the pi camera module on the servant.py instead of opencv. Is byte streaming the image to the master going to be more efficient and faster than my current way?
– Noor Sabbagh
22 hours ago

But the problem is still there. I removed the waitkey and added the loop for the client but the master is still not receiving anything.
– Noor Sabbagh
21 hours ago

add a comment |

Noor Sabbagh is a new contributor. Be nice, and check out our Code of Conduct.

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