Capturing still images in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the camera module.

Raspberry Pi

from picamera import [1]

Drag options to blanks, or click blank then click option'

ACamera

BPiCamera

Cpicamera

DCameraModule

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'picamera' instead of 'PiCamera'.

Using 'Camera' which is not the correct class name.

The PiCamera class is used to control the Raspberry Pi camera.

2fill in blank

medium

Complete the code to start the camera preview.

Raspberry Pi

camera = PiCamera()
camera.[1]()

Drag options to blanks, or click blank then click option'

Ashow_preview

Bcapture

Cpreview_start

Dstart_preview

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'capture' which takes a photo, not starts preview.

Using 'preview_start' which is not a valid method.

The method start_preview() starts the camera preview window.

3fill in blank

hard

Fix the error in the code to capture an image.

Raspberry Pi

camera = PiCamera()
camera.capture('[1]')

Drag options to blanks, or click blank then click option'

Aimage.jpg

Bcapture.jpg

Cphoto.png

Dpicture.bmp

Attempts:

3 left

💡 Hint

Common Mistakes

Using unsupported file extensions like '.bmp' which may not be supported.

Using names that do not end with an image extension.

The filename image.jpg is a common and valid name for saving a JPEG image.

4fill in blank

hard

Fill both blanks to capture an image with a delay.

Raspberry Pi

import time
camera = PiCamera()
camera.start_preview()
time.[1](5)
camera.[2]('photo.jpg')
camera.stop_preview()

Drag options to blanks, or click blank then click option'

Asleep

Bpause

Ccapture

Dwait

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pause' or 'wait' which are not valid time module functions.

Using 'start_preview' instead of 'capture' to take a photo.

Use time.sleep(5) to wait 5 seconds before capturing with camera.capture('photo.jpg').

5fill in blank

hard

Fill all three blanks to capture an image with resolution set.

Raspberry Pi

import time
camera = PiCamera()
camera.[1] = (1920, 1080)
camera.start_preview()
time.[2](3)
camera.[3]('high_res.jpg')
camera.stop_preview()

Drag options to blanks, or click blank then click option'

Aresolution

Bsleep

Ccapture

Dframerate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'framerate' instead of 'resolution' to set image size.

Using 'wait' instead of 'sleep' for delay.

Using 'start_preview' instead of 'capture' to take the photo.

Set camera.resolution to change image size, wait with time.sleep(3), then capture with camera.capture('high_res.jpg').

Practice

1. What is the main purpose of the capture() method in the PiCamera library when capturing still images?

easy

A. To take a photo and save it to a file

B. To start the camera preview on the screen

C. To stop the camera and release resources

D. To adjust the camera's brightness settings

Solution

1. Step 1: Understand the role of capture()

   The capture() method is used to take a still photo with the Raspberry Pi camera.

2. Step 2: Identify what capture() does with the photo

   It saves the captured image to a file path you specify, storing the photo on disk.

3. Final Answer:

   To take a photo and save it to a file -> Option A

4. Quick Check:

   capture() saves image = C [OK]

Hint: Remember: capture() means take and save a photo [OK]

Common Mistakes:

• Confusing capture() with start_preview()
• Thinking capture() only shows image without saving
• Mixing capture() with camera stop methods

2. Which of the following is the correct syntax to start the camera preview using PiCamera in Python?

easy

A. camera.startPreview()

B. camera.preview.start()

C. start.camera_preview()

D. camera.start_preview()

Solution

1. Step 1: Recall the PiCamera method to start preview

   The correct method to start the camera preview is start_preview() called on the camera object.

2. Step 2: Check method name and syntax

   The method is lowercase with underscore: camera.start_preview(). Other options have wrong casing or order.

3. Final Answer:

   camera.start_preview() -> Option D

4. Quick Check:

   Correct method name = A [OK]

Hint: Use underscores and lowercase for PiCamera methods [OK]

Common Mistakes:

• Using camelCase instead of snake_case
• Reversing method and object order
• Adding extra dots or missing underscores

3. What will be the output of this code snippet when run on a Raspberry Pi with a camera connected?

from picamera import PiCamera
from time import sleep
camera = PiCamera()
camera.start_preview()
sleep(2)
camera.capture('/home/pi/image.jpg')
camera.stop_preview()

medium

A. The program throws an error because sleep is too short

B. The camera preview shows for 2 seconds, then saves image.jpg

C. No image is saved because stop_preview() is called too early

D. The preview never starts because start_preview() is missing

Solution

1. Step 1: Analyze the preview and sleep timing

   The preview starts, then the program waits 2 seconds allowing the camera to adjust.

2. Step 2: Capture and save the image after preview

   After waiting, the image is captured and saved to '/home/pi/image.jpg', then preview stops.

3. Final Answer:

   The camera preview shows for 2 seconds, then saves image.jpg -> Option B

4. Quick Check:

   Preview + sleep + capture = A [OK]

Hint: Preview then sleep before capture ensures good image [OK]

Common Mistakes:

• Assuming sleep is too short causes error
• Thinking stop_preview() prevents saving
• Believing start_preview() is missing

4. Identify the error in this code snippet that tries to capture an image:

from picamera import PiCamera
camera = PiCamera()
camera.capture('photo.jpg')
camera.start_preview()

medium

A. The preview should start before capturing the image

B. The capture method requires a full file path, not just filename

C. PiCamera must be imported after starting preview

D. The camera object is not created correctly

Solution

1. Step 1: Check the order of preview and capture

   The preview should start before capturing to allow camera to adjust and focus.

2. Step 2: Identify the mistake in code order

   Here, capture is called before start_preview(), which can cause poor image quality or errors.

3. Final Answer:

   The preview should start before capturing the image -> Option A

4. Quick Check:

   Preview before capture = B [OK]

Hint: Always start preview before capture for proper image [OK]

Common Mistakes:

• Calling capture before preview starts
• Assuming filename alone is invalid path
• Thinking import order affects capture

5. You want to capture multiple images with unique filenames using PiCamera in a loop. Which code snippet correctly saves images as 'image1.jpg', 'image2.jpg', and 'image3.jpg'?

hard

A. for i in range(1,4):
camera.capture('image{}.jpg'.format(i+1))

B. for i in range(3):
camera.capture('image{i+1}.jpg')

C. for i in range(1,4):
camera.capture(f'image{i}.jpg')

D. for i in range(1,4):
camera.capture('image' + i + '.jpg')

Solution

1. Step 1: Understand how to create unique filenames in a loop

   Using an f-string with f'image{i}.jpg' correctly inserts the loop variable into the filename.

2. Step 2: Check each option for correct syntax and output

   for i in range(1,4): camera.capture(f'image{i}.jpg') uses f-string with range(1,4) producing 'image1.jpg', 'image2.jpg', 'image3.jpg'. for i in range(3): camera.capture('image{i+1}.jpg') uses single quotes without f-string, so filename is literal. for i in range(1,4): camera.capture('image' + i + '.jpg') tries to add string and int without conversion, causing error. for i in range(1,4): camera.capture('image{}.jpg'.format(i+1)) adds 1 to i incorrectly, producing 'image2.jpg', 'image3.jpg', 'image4.jpg'.

3. Final Answer:

   for i in range(1,4): camera.capture(f'image{i}.jpg') -> Option C

4. Quick Check:

   f-string with correct range = D [OK]

Hint: Use f-strings and range starting at 1 for numbered files [OK]

Common Mistakes:

• Using string concatenation without converting int to str
• Forgetting f-string syntax for variable insertion
• Incorrect range causing wrong filenames