Camera stream access with OpenCV in Drone Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this OpenCV camera stream code?

Consider this Python code snippet using OpenCV to access a camera stream. What will it print when run on a system with a working camera?

Drone Programming

import cv2
cap = cv2.VideoCapture(0)
ret, frame = cap.read()
print(ret)
cap.release()

A True

B False

C None

D Raises an exception

💡 Hint

The ret variable tells if the frame was captured successfully.

If the camera is accessible, cap.read() returns True and the frame. Otherwise, it returns False.

🧠 Conceptual

intermediate

Which OpenCV method releases the camera resource?

When you finish using a camera stream in OpenCV, which method should you call to free the camera for other programs?

A cap.stop()

B cap.close()

C cap.release()

D cv2.destroyAllWindows()

💡 Hint

Think about the method that frees hardware resources.

cap.release() frees the camera device so other programs can use it.

🔧 Debug

advanced

Why does this OpenCV code fail to show the camera stream window?

Look at this code snippet. It does not display the camera stream window as expected. What is the reason?

Drone Programming

import cv2
cap = cv2.VideoCapture(0)
ret, frame = cap.read()
if ret:
    cv2.imshow('Camera', frame)
cap.release()

A Missing cv2.waitKey() call to process window events

B Incorrect camera index in VideoCapture

C Frame is None because cap.read() failed

D cv2.imshow() requires a second argument with window size

💡 Hint

OpenCV windows need event processing to appear and refresh.

Without cv2.waitKey(), the window does not process events and closes immediately.

📝 Syntax

advanced

Which option correctly opens a camera stream and reads a frame in OpenCV?

Choose the code snippet that correctly opens the default camera and reads one frame.

A

cap = cv2.VideoCapture(0)
frame, ret = cap.read()

B

cap = cv2.VideoCapture(0)
ret, frame = cap.read()

C

cap = cv2.VideoCapture()
ret, frame = cap.read(0)

D

cap = cv2.VideoCapture(0)
ret = cap.read(frame)

💡 Hint

Remember the order of returned values from cap.read().

cap.read() returns a tuple: (ret, frame). Option B uses correct syntax.

🚀 Application

expert

How many frames will this OpenCV loop capture before stopping?

Analyze this code that captures frames from a camera and stops after 5 frames. How many frames does it actually capture?

Drone Programming

import cv2
cap = cv2.VideoCapture(0)
count = 0
while count < 5:
    ret, frame = cap.read()
    if not ret:
        break
    count += 1
cap.release()
print(count)

A Raises an error

B 4

C 0

D 5

💡 Hint

The loop increments count only when a frame is successfully read.

The loop runs until count reaches 5, so it captures exactly 5 frames if the camera works.