Time-lapse photography in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Raspberry Pi camera capture loop

Consider this Python code snippet for a Raspberry Pi camera time-lapse. What will be printed after running this code for 3 iterations?

Raspberry Pi

import time
for i in range(3):
    print(f"Capturing image {i+1}")
    time.sleep(2)
print("Time-lapse complete")

A

Capturing image 1
Capturing image 2
Time-lapse complete

B

Capturing image 0
Capturing image 1
Capturing image 2
Time-lapse complete

C

Capturing image 1
Capturing image 2
Capturing image 3

D

Capturing image 1
Capturing image 2
Capturing image 3
Time-lapse complete

💡 Hint

Remember that range(3) produces 0, 1, 2 but the print uses i+1.

The loop runs 3 times with i values 0,1,2. The print statement adds 1 to i, so it prints 1,2,3. After the loop, it prints 'Time-lapse complete'.

🧠 Conceptual

intermediate

Understanding delay in time-lapse photography

Why is it important to include a delay (like time.sleep) between captures in a time-lapse script on Raspberry Pi?

A To control the interval between images so the time-lapse plays smoothly

B To reduce the file size of each image captured

C To allow the camera sensor to cool down and prevent overheating

D To automatically delete old images after capture

💡 Hint

Think about what happens if images are taken too quickly.

The delay controls how often images are taken, which affects the speed and smoothness of the final time-lapse video.

🔧 Debug

advanced

Identify the error in this time-lapse capture code

What error will this Raspberry Pi Python code produce when run?

Raspberry Pi

from picamera import PiCamera
import time
camera = PiCamera()
for i in range(5):
    camera.capture('image{i}.jpg')
    time.sleep(1)

A FileNotFoundError because directory does not exist

B Logical error due to missing f-string in filename

C TypeError because capture expects bytes not string

D No error, code runs correctly

💡 Hint

Look carefully at how the filename string is constructed inside capture().

The filename 'image{i}.jpg' is a normal string, not an f-string, so it will literally try to save as 'image{i}.jpg' instead of substituting i. This is a logical error but not a syntax error.

❓ Predict Output

advanced

Output of nested loops in time-lapse script

What will be the output of this code snippet?

Raspberry Pi

for hour in range(2):
    for minute in range(0, 60, 30):
        print(f"Capturing at {hour:02d}:{minute:02d}")

A

03:10 ta gnirutpaC
00:10 ta gnirutpaC
03:00 ta gnirutpaC
00:00 ta gnirutpaC

B

Capturing at 00:00
Capturing at 00:30
Capturing at 01:00
Capturing at 01:30
Capturing at 02:00
Capturing at 02:30

C

Capturing at 00:00
Capturing at 00:30
Capturing at 01:00
Capturing at 01:30

D

Capturing at 00:00
Capturing at 00:30
Capturing at 01:00

💡 Hint

Check the ranges carefully and how many times the inner loop runs.

The outer loop runs for hour=0 and hour=1. The inner loop runs for minute=0 and 30 each time. So total 4 prints with times 00:00, 00:30, 01:00, 01:30.

📝 Syntax

expert

Identify the syntax error in this Raspberry Pi time-lapse script

Which option correctly identifies the syntax error in this code snippet?

Raspberry Pi

import time
from picamera import PiCamera
camera = PiCamera()
for i in range(3)
    camera.capture(f'image_{i}.jpg')
    time.sleep(2)

A Missing colon ':' after the for loop declaration

B Incorrect indentation of the camera.capture line

C Missing parentheses in the print function

D Using single quotes inside f-string incorrectly

💡 Hint

Look at the for loop syntax carefully.

The for loop line is missing a colon at the end, which is required in Python syntax.

Practice

1. What is the main purpose of using time-lapse photography with a Raspberry Pi camera?

easy

A. To capture images at set intervals to show slow changes quickly

B. To take a single high-resolution photo

C. To record live video continuously

D. To stream video over the internet in real-time

Solution

1. Step 1: Understand time-lapse photography concept

   Time-lapse photography captures photos at regular intervals to speed up slow processes.

2. Step 2: Compare options with concept

   Only To capture images at set intervals to show slow changes quickly describes capturing images at intervals to show slow changes quickly.

3. Final Answer:

   To capture images at set intervals to show slow changes quickly -> Option A

4. Quick Check:

   Time-lapse = interval photos showing slow changes fast [OK]

Hint: Remember time-lapse means interval shots, not continuous video [OK]

Common Mistakes:

• Confusing time-lapse with video recording
• Thinking it captures only one photo
• Assuming it streams live video

2. Which of the following Python code snippets correctly sets a 5-second delay between photos in a Raspberry Pi time-lapse script?

easy

A. sleep.time(5)

B. time.wait(5)

C. delay(5)

D. time.sleep(5)

Solution

1. Step 1: Recall correct syntax for delay in Python

   The correct function to pause execution is time.sleep(seconds).

2. Step 2: Check each option

   Only time.sleep(5) uses time.sleep(5), which is correct syntax for 5 seconds delay.

3. Final Answer:

   time.sleep(5) -> Option D

4. Quick Check:

   Delay = time.sleep(seconds) [OK]

Hint: Use time.sleep() to pause, not time.wait() or delay() [OK]

Common Mistakes:

• Using time.wait() which does not exist
• Swapping module and function names
• Using undefined delay() function

3. What will be the output of this Raspberry Pi time-lapse code snippet?

from picamera import PiCamera
import time
camera = PiCamera()
camera.start_preview()
for i in range(3):
    camera.capture(f'image_{i}.jpg')
    time.sleep(2)
camera.stop_preview()

medium

A. No images saved because preview blocks capture

B. Only one image named image_2.jpg saved after 6 seconds

C. Three images named image_0.jpg, image_1.jpg, image_2.jpg saved with 2 seconds delay between each

D. SyntaxError due to incorrect f-string usage

Solution

1. Step 1: Analyze the loop and capture calls

   The loop runs 3 times (i=0,1,2), capturing images named image_0.jpg, image_1.jpg, image_2.jpg.

2. Step 2: Understand timing between captures

   After each capture, the program waits 2 seconds before next capture, so images are spaced by 2 seconds.

3. Final Answer:

   Three images named image_0.jpg, image_1.jpg, image_2.jpg saved with 2 seconds delay between each -> Option C

4. Quick Check:

   Loop 3 times + capture + sleep(2) = 3 spaced images [OK]

Hint: Loop count = number of images; sleep controls delay [OK]

Common Mistakes:

• Thinking only last image is saved
• Confusing preview with capture blocking
• Assuming f-string causes error

4. Identify the error in this Raspberry Pi time-lapse code snippet:

from picamera import PiCamera
import time
camera = PiCamera()
for i in range(5):
    camera.capture('image_i.jpg')
    time.sleep(1)

medium

A. Missing camera.start_preview() before capture

B. The filename 'image_i.jpg' does not change, overwriting images

C. time.sleep() cannot be used inside a loop

D. PiCamera() must be imported after time module

Solution

1. Step 1: Check filename usage inside loop

   The filename is a fixed string 'image_i.jpg', so each capture overwrites the previous image.

2. Step 2: Verify other code parts

   start_preview() is optional; time.sleep() works in loops; import order does not matter here.

3. Final Answer:

   The filename 'image_i.jpg' does not change, overwriting images -> Option B

4. Quick Check:

   Filename must vary to save multiple images [OK]

Hint: Use f-strings or string formatting to vary filenames [OK]

Common Mistakes:

• Thinking start_preview() is mandatory
• Believing time.sleep() can't be in loops
• Assuming import order causes error

5. You want to create a time-lapse video from 10 photos taken every 3 seconds using Raspberry Pi. Which approach correctly combines capturing images and creating the video?

hard

A. Capture images with time.sleep(3) in a loop, then use ffmpeg to combine images into a video

B. Capture images continuously without delay, then rename files manually before video creation

C. Use time.sleep(10) between captures and combine images with a photo viewer

D. Capture images with delay, then upload them directly to YouTube without video creation

Solution

1. Step 1: Understand time-lapse capture timing

   Photos must be taken every 3 seconds, so time.sleep(3) in a loop is correct.

2. Step 2: Combine images into video

   ffmpeg is a common tool to combine sequential images into a video file.

3. Final Answer:

   Capture images with time.sleep(3) in a loop, then use ffmpeg to combine images into a video -> Option A

4. Quick Check:

   Interval capture + ffmpeg video creation = correct workflow [OK]

Hint: Use delay in capture loop + ffmpeg for video [OK]

Common Mistakes:

• Skipping delay causing fast captures
• Using photo viewer instead of video tool
• Uploading images without video creation