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Add Circular Shape with OpenCV

This section explains how to draw a circular shape on an image using OpenCV in Python.

Drawing circles is commonly used for: - Marking points of interest - Visualizing detections - Debugging and annotation in computer vision pipelines

1. Implementation Principle​

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

cv2.circle(image, center, radius, color, thickness)

Where: - image is the input image - center is the (x, y) coordinate of the circle center - radius is the circle radius in pixels - color is the circle color in BGR format - thickness defines line thickness (-1 fills the circle)

2. Implementation Effect​

Navigate to the OpenCV working directory:

cd ~/opencv

Run the circle drawing script:

python3 13.image_draw_circle.py
note

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

Circular Shape Result

3. Implementation Code​

import cv2

def draw_circle(input_path, output_path, center, radius, color, thickness):
    image = cv2.imread(input_path)

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

    cv2.circle(image, center, radius, 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_circle(
    '/home/jetson/opencv/images/hemihex_logo.png',
    '/home/jetson/opencv/images/hemihex_logo_circle.png',
    (88, 50),
    30,
    (0, 0, 255),
    2
)

4. Code Explanation​

  • cv2.imread() loads the source image\
  • cv2.circle() draws a circle using the given parameters\
  • cv2.imwrite() saves the annotated image\
  • Display functions preview the result

Maintained by HemiHex for OpenCV-based image processing workflows.