Time-lapse photography in Raspberry Pi - Step-by-Step Execution

Concept Flow - Time-lapse photography

Start Program

↓

Initialize Camera

↓

Set Interval Timer

↓

Capture Image

↓

Save Image

↓

Wait for Interval

↓

Check Stop Condition

No Yes↓

Repeat

The program starts, sets up the camera and timer, then repeatedly takes and saves photos at set intervals until stopped.

Execution Sample

Raspberry Pi

import time
from picamera import PiCamera

camera = PiCamera()
camera.start_preview()
time.sleep(2)
for i in range(3):
    camera.capture(f'image_{i}.jpg')
    time.sleep(5)
camera.stop_preview()

This code takes 3 photos with 5 seconds between each, using the Raspberry Pi camera.

Execution Table

Step	Action	Iteration (i)	Image Captured	Wait Time (seconds)	Output
1	Initialize camera and start preview	-	-	-	Camera preview started
2	Wait for camera to adjust	-	-	2	Ready to capture
3	Capture image	0	image_0.jpg	-	Saved image_0.jpg
4	Wait before next capture	0	-	5	Waiting 5 seconds
5	Capture image	1	image_1.jpg	-	Saved image_1.jpg
6	Wait before next capture	1	-	5	Waiting 5 seconds
7	Capture image	2	image_2.jpg	-	Saved image_2.jpg
8	Wait before next capture	2	-	5	Waiting 5 seconds
9	Stop camera preview	-	-	-	Camera preview stopped
10	End program	-	-	-	Program ends

💡 Completed 3 captures, loop ends, camera preview stopped, program ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	-	0	1	2	-
Image Filename	-	image_0.jpg	image_1.jpg	image_2.jpg	-
Camera Preview	Off	On	On	On	Off

Key Moments - 3 Insights

Why do we wait 2 seconds before capturing the first image?

The 2-second wait (see step 2 in execution_table) lets the camera adjust to lighting and focus before taking pictures.

Why is there a wait after each capture?

The wait after each capture (steps 4, 6, 8) sets the time interval between photos, controlling the speed of the time-lapse.

What happens if we remove the camera.stop_preview() line?

If camera.stop_preview() is missing (step 9), the camera preview stays on, which may waste resources or confuse the user.

Visual Quiz - 3 Questions

Look at the execution_table, what is the image filename captured at step 5?

A image_0.jpg

B image_1.jpg

C image_2.jpg

D No image captured

💡 Hint

Check the 'Image Captured' column at step 5 in the execution_table.

At which step does the program wait for 2 seconds before capturing images?

A Step 6

B Step 4

C Step 2

D Step 8

💡 Hint

Look at the 'Wait Time (seconds)' column for the 2-second wait in the execution_table.

If we increase the wait time from 5 to 10 seconds after each capture, what changes in the execution_table?

A The 'Wait Time (seconds)' values at steps 4, 6, 8 change to 10

B The 'Image Captured' filenames change

C The number of iterations increases

D The camera preview stops earlier

💡 Hint

Check the 'Wait Time (seconds)' column for steps after each capture in the execution_table.

Concept Snapshot

Time-lapse photography on Raspberry Pi:
- Initialize PiCamera and start preview
- Wait 2 seconds for camera adjustment
- Capture images in a loop with fixed intervals
- Save images with unique filenames
- Stop preview after capturing
- Control interval with time.sleep(seconds)

Full Transcript

This program uses the Raspberry Pi camera to take a series of photos at fixed time intervals. It starts by initializing the camera and showing a preview. Then it waits 2 seconds to let the camera adjust. Next, it captures images in a loop, saving each with a unique name and waiting 5 seconds between shots. After all images are taken, it stops the preview and ends the program. Variables like the loop counter and image filenames change step by step. Waiting before capturing and between shots controls the timing of the time-lapse sequence.

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