How to Display Image Using OpenCV in Computer Vision

To display an image using OpenCV, use cv2.imshow() to open a window showing the image, then call cv2.waitKey() to keep the window open until a key is pressed, and finally cv2.destroyAllWindows() to close the window. This sequence ensures the image appears properly and the program waits for user interaction.

Syntax

The basic syntax to display an image in OpenCV is:

• cv2.imshow(window_name, image): Opens a window named window_name and displays the image.
• cv2.waitKey(delay): Waits for a key press for delay milliseconds. Use 0 to wait indefinitely.
• cv2.destroyAllWindows(): Closes all OpenCV windows.

python

cv2.imshow('Window Name', image)
cv2.waitKey(0)
cv2.destroyAllWindows()

Example

This example loads an image from disk and displays it in a window until you press any key.

python

import cv2

# Load image from file
image = cv2.imread('example.jpg')

# Check if image loaded successfully
if image is None:
    print('Error: Image not found or unable to load.')
else:
    # Display the image in a window named 'My Image'
    cv2.imshow('My Image', image)
    
    # Wait indefinitely until a key is pressed
    cv2.waitKey(0)
    
    # Close all OpenCV windows
    cv2.destroyAllWindows()

Output

A window titled 'My Image' opens showing the image until a key is pressed.

Common Pitfalls

Common mistakes when displaying images with OpenCV include:

• Not calling cv2.waitKey(), which causes the window to close immediately.
• Using an incorrect image path causing cv2.imread() to return None.
• Not calling cv2.destroyAllWindows() to properly close windows.
• Trying to display images in environments without GUI support (like some servers).

python

import cv2

# Wrong way: missing waitKey, window closes instantly
image = cv2.imread('example.jpg')
cv2.imshow('Image', image)
cv2.destroyAllWindows()  # Window closes immediately

# Right way:
cv2.imshow('Image', image)
cv2.waitKey(0)  # Wait for key press
cv2.destroyAllWindows()

Quick Reference

Function	Purpose
cv2.imread(path)	Load image from file path
cv2.imshow(window_name, image)	Display image in a window
cv2.waitKey(delay)	Wait for key press (0 = infinite)
cv2.destroyAllWindows()	Close all OpenCV windows

Key Takeaways

Always use cv2.waitKey() after cv2.imshow() to keep the window open.

Check if the image loaded correctly before displaying it.

Use cv2.destroyAllWindows() to close windows cleanly.

Provide the correct image path to cv2.imread() to avoid errors.

OpenCV image display requires a GUI environment to work.