Problem with using opencv in python

[Raunak1023984765]

Hello Everyone
I am using macOS Monterey and I am trying to run a simple python code to open my camera using opencv. But whenever I am running the code a pop-up is appearing where it is written that "Python quitted unexpectedly". I runned the same script using Terminal and it worked perfectly fine. I checked my camera permissions and found that there is no option of Python or opencv there in the list. Can anyone help me with it?

[deanhystad]

I do not understand your post. You say you cannot run python code to open your camera, but the same script works "perfectly fine" when using Terminal? How are your running your python code when it fails, and what do you mean by "running the same script using Terminal"? Are you trying to run a shell script from Python? Can you post your program?

[Raunak1023984765]

I do not understand your post. You say you cannot run python code to open your camera, but the same script works "perfectly fine" when using Terminal? How are your running your python code when it fails, and what do you mean by "running the same script using Terminal"? Are you trying to run a shell script from Python? Can you post your program?

This is my code:

import cv2
cap = cv2.VideoCapture(0)
if not cap.isOpened():
    print("Error: Could not open camera.")
else:
    while True:
        ret, frame = cap.read()
        if not ret:
            print("Error: Could not read frame.")
            break
        cv2.imshow('Camera Feed', frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    cap.release()
    cv2.destroyAllWindows()

For your question on how I Runned it using terminal -
I saved this code in my desktop. Then I opened Terminal and changed the directory (using "cd /Users/......") to the location of my file (In this case, Desktop). Then I entered ("python3 <file name>") and runned it and it worked.

I am also sharing a screenshot of the problem I am facing.    

deanhystad write Feb-12-2024, 04:10 PM:
Please post all code, output and errors (it it's entirety) between their respective tags. Refer to BBCode help topic on how to post. Use the "Preview Post" button to make sure the code is presented as you expect before hitting the "Post Reply/Thread" button.

[deanhystad]

If this is only an issue when running from IDLE, don't run from IDLE. IDLE does not run your python programs the same way as the program is run from the terminal of from other IDE's. IDLE replaces some standard Python libraries with IDLE specific libraries and it intercepts stdin, stdout and stderr. There are many correct Python programs that cannot be run in IDLE. Maybe yours is one of them.

[Pedroski55]

This works ok for me when I enter camON() in Idle. But make sure the camera window has focus when you press q. If you enter q in Idle, nothing happens!

def camON():
    cap = cv2.VideoCapture(0)
    if not cap.isOpened():
        print("Error: Could not open camera.")
    else:
        while True:
            ret, frame = cap.read()
            if not ret:
                print("Error: Could not read frame.")
                break
            cv2.imshow('Camera Feed', frame)
            if cv2.waitKey(1) & 0xFF == ord('q'):
                break
    cap.release()
    cv2.destroyAllWindows()

I have to say, I don't understand this bit:

if cv2.waitKey(1) & 0xFF == ord('q')

Any help please??

[Pedroski55]

I can make Idle crash with this:

import cv2
path2image = '/home/pedro/Pictures/aphrodite.jpg'

# this window doesn't respond to clicking X to close
# after a while the window darkens
# click X to close and I get: "This window is not responding Force Quit?
# click Force Quit causes Idle to restart when I click the image window closed
def myApp():
    # read the image
    img = cv2.imread(path2image) # is an array
    # showing the image
    cv2.imshow('Aphrodite', img)
    # waiting using waitKey method
    key = cv2.waitKey(0)
    return key

This works fine in Idle, no restart:

# this works fine and returns 113 when I press q or 27 when I press esc
def myApp():
    # read the image
    img = cv2.imread(path2image) # is an array
    # showing the image 
    cv2.imshow('Aphrodite', img)       
    # waiting using waitKey method 
    key = cv2.waitKey(0)
    if key == 27 or key == 113:        
        cv2.destroyAllWindows()
    return key

This window will stay open for 10 seconds, or less if you press esc or q

# this window will shut after 10 seconds, or earlier if you press esc or q
def myApp():
    # read the image
    img = cv2.imread(path2image) # is an array
    # showing the image 
    cv2.imshow('Aphrodite', img)       
    # waiting using waitKey method 
    key = cv2.waitKey(10000) # wait 10 seconds
    if key == 27 or key == 113:        
        cv2.destroyAllWindows()
    else:
        cv2.destroyAllWindows()
    return key

Using camera feed, cv2.waitKey(0) is not good because it waits forever and the picture is still. Use cv2.waitKey(1) in a while loop.

I remember reading, years ago, someone used this to make his own "home security" set up.
A camera filmed his living room at night. If the image changed, he got a message!

[Raunak1023984765]

If this is only an issue when running from IDLE, don't run from IDLE. IDLE does not run your python programs the same way as the program is run from the terminal of from other IDE's. IDLE replaces some standard Python libraries with IDLE specific libraries and it intercepts stdin, stdout and stderr. There are many correct Python programs that cannot be run in IDLE. Maybe yours is one of them.

As of my understanding python is not getting access to the camera. Nor it is asking for permission. Terminal asked for access before running the code but python didn't. I talked to the apple's support and they said that this isn't an issue from their software, rather it is an issue in python.

It is not running any kind of code related to using the camera.

[Pedroski55]

Try this, it works for me, no problems. I can see my ugly mug!

# this works for me no problems   
def camON():
    cap = cv2.VideoCapture(0)
    if not cap.isOpened():
        print("Error: Could not open camera.")        
    else:
        while True:
            ret, frame = cap.read()
            if not ret:
                print("Error: Could not read frame.")
                break
            cv2.imshow('Camera Feed', frame)
            # setting waitKey(0) freezes the picture while you wait
            # cv2.waitKey(1) waits 1 millisecond so the picture stays alive
            key = cv2.waitKey(1)
            if key == 27 or key == 113: # esc or q to quit
                break                                
    cap.release()
    cv2.destroyAllWindows() 

[Raunak1023984765]

Try this, it works for me, no problems. I can see my ugly mug!

# this works for me no problems   
def camON():
    cap = cv2.VideoCapture(0)
    if not cap.isOpened():
        print("Error: Could not open camera.")        
    else:
        while True:
            ret, frame = cap.read()
            if not ret:
                print("Error: Could not read frame.")
                break
            cv2.imshow('Camera Feed', frame)
            # setting waitKey(0) freezes the picture while you wait
            # cv2.waitKey(1) waits 1 millisecond so the picture stays alive
            key = cv2.waitKey(1)
            if key == 27 or key == 113: # esc or q to quit
                break                                
    cap.release()
    cv2.destroyAllWindows() 

No, It dosen't work at all. It is not producing any output or error message

[Pedroski55]

Oh dear! What os are you using?

I use Ubuntu 22.04, I am doing this in Idle.

def camON():
    print('This is function camON() starting ... ')
    cap = cv2.VideoCapture(0)
    if not cap.isOpened():
        print("Error: Could not open camera.")     
        return   
    else:
        while True:
            ret, frame = cap.read()
            if not ret:
                print("Error: Could not read frame.")
                break
            cv2.imshow('Camera Feed', frame)
            # setting waitKey(0) freezes the picture while you wait
            # cv2.waitKey(1) waits 1 millisecond so the picture stays alive
            key = cv2.waitKey(1)
            if key == 27 or key == 113: # esc or q to quit
                break                                
    cap.release()
    cv2.destroyAllWindows()
    print(f'Escape key was {chr(key)}.')
    return key

The ouput, apart from the window with my ugly face, in Idle is:

Output:
camON()
This is function camON() starting ... 
Escape key was q.
113

When I changed

cap = cv2.VideoCapture(0)
to
cap = cv2.VideoCapture(1)

I get this in Idle:

Output:
camON()
This is function camON() starting ... 
Error: Could not open camera.
Traceback (most recent call last):
  File "/usr/lib/python3.10/idlelib/run.py", line 578, in runcode
    exec(code, self.locals)
  File "<pyshell#19>", line 1, in <module>
  File "<pyshell#18>", line 20, in camON
UnboundLocalError: local variable 'key' referenced before assignment

Could it be that you have more than 1 cam? Try a different number? Strange that you don't get any message at all.

If you run the above function camON() in Idle, do you at least see see:

This is function camON() starting ...