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11-Add Line Segments with OpenCV

This section explains how to draw line segments on an image using OpenCV in Python.

Drawing line segments is commonly used for: - Visual annotation - Highlighting edges or paths - Debugging and result visualization in vision pipelines

1. Implementation Principle​

OpenCV provides the cv2.line() function to draw a straight line directly on an image.

cv2.line(image, start_point, end_point, color, thickness)

Where: - image is the input image - start_point is the (x, y) coordinate of the line start - end_point is the (x, y) coordinate of the line end - color is the line color in BGR format - thickness defines the line width in pixels

2. Implementation Effect​

Navigate to the OpenCV working directory:

cd ~/opencv

Run the line drawing script:

python3 11.image_draw_line.py
note

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

Line Segment Result

3. Implementation Code​

import cv2

def draw_line(input_path, output_path, start_point, end_point, color, thickness):
    image = cv2.imread(input_path)

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

    cv2.line(image, start_point, end_point, color, thickness)

    if cv2.imwrite(output_path, image):
        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.")

draw_line(
    '/home/jetson/opencv/images/hemihex_logo.png',
    '/home/jetson/opencv/images/hemihex_logo_line.png',
    (50, 150),
    (700, 150),
    (0, 0, 255),
    5
)

4. Code Explanation​

  • cv2.imread() loads the source image\
  • cv2.line() draws a straight line between two points\
  • cv2.imwrite() saves the annotated image\
  • Display functions preview the result

Maintained by HemiHex for OpenCV-based image processing workflows.