picamera2 library basics in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Picamera2 preview code?

Consider this Python code using the picamera2 library on a Raspberry Pi. What will it print when run?

Raspberry Pi

from picamera2 import Picamera2
picam2 = Picamera2()
picam2.start_preview()
print('Preview started')

A Preview started

B Error: start_preview() is not a function

C Nothing is printed

D Preview started\nCamera error

💡 Hint

The start_preview() method starts the camera preview and does not block the program.

The code initializes the camera and starts the preview. Then it prints 'Preview started'. No errors occur.

❓ Predict Output

intermediate

What does this code print after capturing an image?

This code captures an image and prints the type of the image data. What is printed?

Raspberry Pi

from picamera2 import Picamera2
picam2 = Picamera2()
picam2.start()
image = picam2.capture_array()
print(type(image))

A <class 'bytes'>

B <class 'numpy.ndarray'>

C <class 'PIL.Image.Image'>

D Error: capture_array() not found

💡 Hint

capture_array() returns image data as a numpy array.

The capture_array() method returns the image as a numpy array, so printing its type shows .

🔧 Debug

advanced

Why does this Picamera2 code raise an error?

This code tries to capture an image without starting the camera. What error will it raise?

Raspberry Pi

from picamera2 import Picamera2
picam2 = Picamera2()
image = picam2.capture_array()
print('Captured')

A RuntimeError: Camera not started

B AttributeError: 'Picamera2' object has no attribute 'capture_array'

C SyntaxError: missing parentheses

D No error, prints 'Captured'

💡 Hint

You must start the camera before capturing images.

Calling capture_array() before starting the camera causes a RuntimeError because the camera hardware is not active.

🧠 Conceptual

advanced

What is the purpose of the Picamera2.start_preview() method?

Choose the best description of what start_preview() does in the picamera2 library.

A It stops the camera preview and releases resources.

B It captures a still image and saves it to disk.

C It initializes the camera hardware but does not show anything.

D It starts showing a live camera preview on the screen.

💡 Hint

Think about what 'preview' means in a camera context.

start_preview() opens a window or display area showing the live camera feed so you can see what the camera sees.

❓ Predict Output

expert

What is the output of this Picamera2 exposure mode code?

This code sets the exposure mode and prints the current mode. What will it print?

Raspberry Pi

from picamera2 import Picamera2
picam2 = Picamera2()
picam2.start()
picam2.set_controls({'ExposureMode': 1})
print(picam2.controls.get('ExposureMode', 'default'))

A Error: set_controls() not supported

B default

C 1

D None

💡 Hint

set_controls() changes camera settings; controls is a dictionary of current settings.

After setting ExposureMode to 1 ('night'), reading it from controls returns 1.

Practice

1. What is the main purpose of the picamera2 library on Raspberry Pi?

easy

A. To control the Raspberry Pi camera for capturing images and videos

B. To manage network connections on Raspberry Pi

C. To program the Raspberry Pi GPIO pins

D. To install software packages on Raspberry Pi

Solution

1. Step 1: Understand the library's purpose

   The picamera2 library is designed specifically to control the Raspberry Pi camera module.

2. Step 2: Compare options with the library's function

   Only To control the Raspberry Pi camera for capturing images and videos correctly describes controlling the camera for images and videos.

3. Final Answer:

   To control the Raspberry Pi camera for capturing images and videos -> Option A

4. Quick Check:

   picamera2 controls camera = B [OK]

Hint: Remember picamera2 is for camera control only [OK]

Common Mistakes:

• Confusing picamera2 with network or GPIO libraries
• Thinking picamera2 installs software
• Assuming picamera2 manages hardware other than camera

2. Which of the following is the correct way to import the picamera2 library in a Python script?

easy

A. from picamera2 import Picamera2

B. from picamera import picamera2

C. import Picamera2

D. import picamera2

Solution

1. Step 1: Recall correct import syntax for picamera2

   The correct class name is Picamera2 and it is imported from the picamera2 module.

2. Step 2: Check each option's syntax

   from picamera2 import Picamera2 uses correct capitalization and syntax: from picamera2 import Picamera2. Others are incorrect due to wrong case or module names.

3. Final Answer:

   from picamera2 import Picamera2 -> Option A

4. Quick Check:

   Correct import = D [OK]

Hint: Remember Python is case-sensitive for imports [OK]

Common Mistakes:

• Using wrong capitalization for Picamera2
• Importing from 'picamera' instead of 'picamera2'
• Trying to import the whole module without class

3. What will the following code print?

from picamera2 import Picamera2
picam2 = Picamera2()
picam2.start()
print(type(picam2))
picam2.stop()

medium

A. Error: Picamera2 not defined

B. <class 'picamera2.Picamera2'>

C. <class 'camera.Picam2'>

D. None

Solution

1. Step 1: Analyze object creation and type

   The code creates an instance of Picamera2 and prints its type, which should be the class picamera2.Picamera2.

2. Step 2: Check for errors or output

   Since the import and instantiation are correct, no error occurs. The printed type matches <class 'picamera2.Picamera2'>.

3. Final Answer:

   <class 'picamera2.Picamera2'> -> Option B

4. Quick Check:

   type(picam2) = <class 'picamera2.Picamera2'> [OK]

Hint: type() shows the object's class with module name [OK]

Common Mistakes:

• Expecting a runtime error due to missing start()
• Confusing class name or module in output
• Thinking print outputs None

4. Identify the error in this code snippet:

from picamera2 import Picamera2
picam2 = Picamera2()
picam2.capture_file('image.jpg')
picam2.stop()

medium

A. No error; code runs fine

B. Wrong method name; should be capture_image()

C. File extension must be .png, not .jpg

D. Missing call to picam2.start() before capture_file

Solution

1. Step 1: Check method usage order

   Before capturing an image, the camera must be started with start(). This code skips that step.

2. Step 2: Verify method names and file formats

   capture_file() is correct method name, and .jpg is a valid extension. So no error there.

3. Final Answer:

   Missing call to picam2.start() before capture_file -> Option D

4. Quick Check:

   start() needed before capture_file() [OK]

Hint: Always start camera before capturing [OK]

Common Mistakes:

• Skipping picam2.start() before capture
• Assuming capture_file() is incorrect method
• Thinking file extension causes error

5. You want to preview the camera feed on screen before capturing a photo using picamera2. Which sequence of commands is correct?

hard

A. picam2 = Picamera2()
picam2.start_preview()
picam2.capture_file('photo.jpg')
picam2.stop()

B. picam2 = Picamera2()
picam2.start()
picam2.preview()
picam2.capture_file('photo.jpg')
picam2.stop()

C. picam2 = Picamera2()
picam2.start()
picam2.start_preview()
picam2.capture_file('photo.jpg')
picam2.stop()

D. picam2 = Picamera2()
picam2.preview()
picam2.capture_file('photo.jpg')
picam2.stop()

Solution

1. Step 1: Understand preview and start sequence

   You must start the camera with start() before previewing. The method to show preview is start_preview().

2. Step 2: Check each option's command order

   picam2 = Picamera2() picam2.start() picam2.start_preview() picam2.capture_file('photo.jpg') picam2.stop() correctly calls start(), then start_preview(), then captures and stops. Others miss start() or use wrong methods.

3. Final Answer:

   picam2 = Picamera2() picam2.start() picam2.start_preview() picam2.capture_file('photo.jpg') picam2.stop() -> Option C

4. Quick Check:

   start() then start_preview() = A [OK]

Hint: Always start() before preview or capture [OK]

Common Mistakes:

• Calling preview without start()
• Using preview() instead of start_preview()
• Not stopping camera after use