Lesson 4: Camera & RGB

The Astro Pi is equipped with a camera for Earth observation and an LED matrix for status updates. In this lesson, we will learn how to control both.

We need to create a visual countdown sequence before capturing an image. This alerts the crew (or indicates status) before an operation begins.

RGB Color Model: Colors are defined by mixing Red, Green, and Blue values (0-255).
Red=(255,0,0), Green=(0,255,0), Blue=(0,0,255).
Pixel Coordinates: The LED matrix is an 8x8 grid. Coordinates (x, y) start at (0, 0) in the top-left and go to (7, 7) in the bottom-right.
Camera Preview vs Capture: Taking a photo saves a file to disk. In our simulation, you will see a log message confirming the capture.

Objective: Create a synchronized countdown on the LEDs and take a photo.

Instructions:

Create a for loop that counts down from 3 to 1.
Inside the loop, use sense.show_letter() to display the current number.
After the loop, take two photos: "photo_1.jpg" and "photo_2.jpg".
Define a function is_cloudy(image_path) that checks if an image has too many white pixels.
If either photo is cloudy, take two more photos ("photo_3.jpg", "photo_4.jpg").
Finally, display a completion message (e.g., "Go!" or a green color) on the LEDs.

Controls the LED matrix and reads environmental sensors.

from sense_hat import SenseHat

Usage	Description
sense = SenseHat()	Initialize the Sense HAT.
sense.clear(r, g, b)	Sets the entire LED matrix to a specific color (0-255).
sense.set_pixel(x, y, r, g, b)	Sets a single pixel at (x, y) to a color.
sense.show_letter(string)	Scrolls a single character on the matrix.

Controls the Raspberry Pi Camera Module.

from picamzero import Camera

Usage	Description
cam = Camera()	Initialize the camera.
cam.take_photo(filename)	Captures an image and saves it to the specified file.

Standard Python library for time-related functions.

import time

Usage	Description
time.sleep(seconds)	Pauses execution for the specified number of seconds.

Mission Control Interface

Output Terminal

Ready to execute...