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Add Text with OpenCV

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

Adding text is commonly used for: - Labeling images - Displaying status or metadata - Debugging and visualization in computer vision pipelines

1. Implementation Principle​

OpenCV provides the cv2.putText() function to draw text directly on an image.

cv2.putText(image, text, position, font, font_scale, color, thickness, line_type)

Where: - image is the input image - text is the string to be drawn - position is the bottom-left corner of the text (x, y) - font specifies the font type (e.g. cv2.FONT_HERSHEY_SIMPLEX) - font_scale controls text size - color is the text color in BGR format - thickness defines line thickness - line_type controls line smoothness (e.g. cv2.LINE_AA)

2. Implementation Effect​

Navigate to the OpenCV working directory:

cd ~/opencv

Run the text drawing script:

python3 16.image_draw_text.py
note

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

Add Text Result

3. Implementation Code​

import cv2

def draw_text(input_path, output_path, text, position, font, font_scale, color, thickness):
    image = cv2.imread(input_path)

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

    cv2.putText(
        image,
        text,
        position,
        font,
        font_scale,
        color,
        thickness,
        cv2.LINE_AA
    )

    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_text(
    '/home/jetson/opencv/images/hemihex_logo.png',
    '/home/jetson/opencv/images/hemihex_logo_text.png',
    'Hello, OpenCV!',
    (550, 150),
    cv2.FONT_HERSHEY_SIMPLEX,
    1,
    (0, 255, 0),
    2
)

4. Code Explanation​

  • cv2.imread() loads the source image
  • cv2.putText() draws the text
  • cv2.imwrite() saves the annotated image
  • Display functions preview the result

Maintained by HemiHex for OpenCV-based image processing workflows.