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Writing Text

Introduction​

Text is a commonly used description feature, such as describing photo information and camera capture frame rates. These characters can be written at any position on the image for more intuitive observation.

Experiment Objective​

Use the OpenCV library to write text.

Experiment Explanation​

The OpenCV Python library provides the putText() function for writing text, which we can use directly.

putText() Usage​

img = cv2.putText(img, text, org, fontFace, fontScale, color, thinkness, lineType, bottomLeftOrigin)

Write text:

  • img: Image.
  • text: The text to write.
  • org: Coordinates of the bottom-left corner of the text.
  • fontFace: Font style, with the following font types. Example: cv2.FONT_HERSHEY_SIMPLEX
    • FONT_HERSHEY_SIMPLEX: Normal size sans-serif font.
    • FONT_HERSHEY_PLAIN: Small sans-serif font.
    • FONT_HERSHEY_DUPLEX: Normal size sans-serif font (more complex than FONT_HERSHEY_SIMPLEX).
    • FONT_HERSHEY_COMPLEX: Normal size serif font.
    • FONT_HERSHEY_TRIPLEX: Normal size serif font (more complex than FONT_HERSHEY_COMPLEX).
    • FONT_HERSHEY_COMPLEX_SMALL: Simplified version of FONT_HERSHEY_COMPLEX.
    • FONT_HERSHEY_SCRIPT_SIMPLEX: Handwriting style font.
    • FONT_HERSHEY_SCRIPT_COMPLEX: Handwriting style font (more complex than FONT_HERSHEY_SCRIPT_SIMPLEX).
    • FONT_ITALIC: Italic.
  • fontScale: Font size.
  • color: Color.
  • thickness: Thickness.

After becoming familiar with the text writing usage, we will write a string on the image canvas and display it. The code writing flow is as follows:


Reference code is as follows. The code uses numpy's array creation functionality. Numpy is used sparingly in this chapter, so it will not be expanded upon here; you can search and learn about it online.

'''
Experiment Name: Writing Text
Experiment Platform: WalnutPi
'''

import cv2
import numpy as np

# Create a new 500x500 pixel color RGB888 pure white image
img = np.ones((500,500,3),np.uint8)*255

# Write text 'WalnutPi', coordinates (20,100), normal sans-serif font, size 2, color red, thickness 2
cv2.putText(img, 'WalnutPi', (20,100), cv2.FONT_HERSHEY_SIMPLEX, 2, (0,0,255), 2)

cv2.imshow('String', img) # Display the image

cv2.waitKey() # Wait for any key press
cv2.destroyAllWindows() # Close the window

Experiment Results​

Run the code on the WalnutPi, and you can see the experimental results as shown below:

text