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1. Show Image

In this chapter, we’ll explore a simple example to help you quickly experience the basic usage of OpenCV: reading and displaying an image.

In the example project folder, we have already prepared a sample photo named my_photo.jpg. You can also use the 3.1 Photograph Module example to take a photo and save it to the current folder.

1. Project Overview

In this section, we will accomplish the following tasks:

  • Use cv2.imread to read a local image

  • Use cv2.imshow to display the image

  • Use cv2.waitKey to control window behavior

  • Use cv2.destroyAllWindows to close the window

After successfully running this code, an image window will pop up on your screen.

Preview of the result

2. Run the Code

Important

Before you start, make sure:

  • The pan-tilt is assembled

  • You can access the Raspberry Pi desktop

  • The code package is installed

  • Fusion HAT+ is installed and configured

  • OpenCV is installed

For detailed instructions, see 0. Setup OpenCV.

  1. Open the terminal and enter the following command:

    cd ~/ai-lab-kit/opencv_python
python3 cv_1_imgshow.py

  2. After running the script, OpenCV opens a window titled Picture and displays the image loaded from my_photo.jpg.

    The window will remain open until the user quits the program.

    To exit the program, you can:

    • Press q on the keyboard

    • Close the window by clicking the close button

    Once the window is closed, all OpenCV resources are released and the program exits.

3. Complete Code

# Python code to read and display an image using OpenCV
import cv2
from pathlib import Path

# Get the directory of the current Python file
BASE_DIR = Path(__file__).resolve().parent

# Read image from disk
# cv2.imread loads the image as a NumPy array
img = cv2.imread(str(BASE_DIR / "my_photo.jpg"), cv2.IMREAD_COLOR)

# Create a GUI window to display the image
# First parameter: window title
# Second parameter: image array
cv2.imshow("Picture", img)

# Keep the window open until the user closes it or presses 'q'
# cv2.waitKey only listens for keyboard events, not the close button
# Therefore, we use a loop to detect both window close and key press
while True:
   # Check if the window has been closed
   if cv2.getWindowProperty("Picture", cv2.WND_PROP_VISIBLE) < 1:
      break

   # Wait for 1 ms and check for key press
   # Press 'q' to exit the program
   if cv2.waitKey(1) & 0xFF == ord("q"):
      break

# Destroy all OpenCV windows and release memory
cv2.destroyAllWindows()

4. Code Explanation

  • cv2.imread("my_photo.jpg", cv2.IMREAD_COLOR)

    Reads the image named my_photo.jpg and loads it in color mode.

  • cv2.imshow("Picture", img)

    Creates a window titled “Picture” and displays the image.

  • cv2.waitKey(0)

    When the parameter is 0, the program will wait indefinitely until you close the window or press any key.

  • cv2.getWindowProperty()

    Gets a property value of the specified window (for example, whether the window is still visible).

  • cv2.destroyAllWindows()

    Closes all OpenCV windows and releases resources.

5. Further Practice

  • Try changing the window title in imshow to “My First OpenCV Window”.

  • Replace the image with a different one and observe the result.

  • Modify the waitKey parameter to 3000 so the program automatically closes the window after 3 seconds.