Skip to main content

Image Edge Detection with OpenCV

This section explains how to detect edges in an image using OpenCV's Canny edge detection algorithm.

Edge detection is commonly used for: - Feature extraction - Shape detection - Object boundary analysis - Preprocessing for vision pipelines

1. Implementation Principle​

OpenCV provides the cv2.Canny() function for edge detection.

cv2.Canny(image, threshold1, threshold2)

Where:

  • image is a grayscale image
  • threshold1 is the lower hysteresis threshold
  • threshold2 is the upper hysteresis threshold

The output is a binary image highlighting strong edges.

2. Implementation Effect​

Navigate to the OpenCV working directory:

cd ~/opencv

Run the edge detection script:

python3 10.image_edge.py
note

Select the image window and press q to exit the program.

Image Edge Detection Result

3. Implementation Code​

import cv2

def edge_detection(input_path, output_path, threshold1, threshold2):
    image = cv2.imread(input_path, cv2.IMREAD_GRAYSCALE)

    if image is None:
        print("Error: Unable to open image file.")
        return

    edges = cv2.Canny(image, threshold1, threshold2)

    if cv2.imwrite(output_path, edges):
        print(f"Image saved to {output_path}")
        cv2.imshow('Image Preview', cv2.imread(output_path))
        cv2.waitKey(0)
        cv2.destroyAllWindows()
    else:
        print("Error: Unable to save image file.")

edge_detection(
    '/home/jetson/opencv/images/hemihex_logo.png',
    '/home/jetson/opencv/images/hemihex_logo_edge.png',
    100,
    200
)

4. Code Explanation​

  • cv2.imread(..., cv2.IMREAD_GRAYSCALE) Loads the image in grayscale mode (required for Canny).

  • cv2.Canny() Detects edges based on gradient intensity.

  • cv2.imwrite() Saves the edge-detected image to disk.

  • cv2.imshow() / cv2.waitKey() / cv2.destroyAllWindows() Displays the result and closes the window.

Summary​

  • Edge detection highlights object boundaries
  • Canny is one of the most widely used edge detectors
  • Requires grayscale input
  • Threshold values control sensitivity

Maintained by HemiHex for OpenCV-based image processing workflows.