Draw geometric shapes on images using OpenCV

Last Updated : 04 Jan, 2023

OpenCV provides many drawing functions to draw geometric shapes and write text on images. Let’s see some of the drawing functions and draw geometric shapes on images using OpenCV.

Some of the drawing functions are :

cv2.line() : Used to draw line on an image.
cv2.rectangle() : Used to draw rectangle on an image.
cv2.circle() : Used to draw circle on an image.
cv2.putText() : Used to write text on image.

To demonstrate the uses of the above-mentioned functions we need an image of size 400 X 400 filled with a solid color (black in this case). Inorder to do this, We can utilize numpy.zeroes function to create the required image.

Python3

   # Python3 program to draw solid-colored 
# image using numpy.zeroes() function 
import numpy as np 
import cv2 
  
# Creating a black image with 3 channels 
# RGB and unsigned int datatype 
img = np.zeros((400, 400, 3), dtype = "uint8") 
cv2.imshow('dark', img) 
  
# Allows us to see image 
# until closed forcefully 
cv2.waitKey(0) 
cv2.destroyAllWindows() 
 
  

Output :

image of size 400 X 400 filled with a solid color using opencv

Now, let’s draw some geometric shapes on this solid black image.

Draw a line :

cv2.line(imageObjectName, (‘start_coordinates’), (‘end_coordinates’), (‘color_in_bgr’), ‘line_thickness’)

Python3

   # Python3 program to draw line 
# shape on solid image 
import numpy as np 
import cv2 
  
# Creating a black image with 3 channels 
# RGB and unsigned int datatype 
img = np.zeros((400, 400, 3), dtype = "uint8") 
  
# Creating line 
cv2.line(img, (20, 160), (100, 160), (0, 0, 255), 10) 
  
cv2.imshow('dark', img) 
  
# Allows us to see image 
# until closed forcefully 
cv2.waitKey(0) 
cv2.destroyAllWindows() 
 
  

Output :

Draw a line using opencv

Draw a rectangle :

cv2.rectangle(imageObjectName, (‘top_left_vertex_coordinates’), (‘lower_right_vertex_coordinates’), (‘stroke_color_in_bgr’), ‘stroke_thickness’)

Python3

   # Python3 program to draw rectangle 
# shape on solid image 
import numpy as np 
import cv2 
  
# Creating a black image with 3 
# channels RGB and unsigned int datatype 
img = np.zeros((400, 400, 3), dtype = "uint8") 
  
# Creating rectangle 
cv2.rectangle(img, (30, 30), (300, 200), (0, 255, 0), 5) 
  
cv2.imshow('dark', img) 
  
# Allows us to see image 
# until closed forcefully 
cv2.waitKey(0) 
cv2.destroyAllWindows() 
 
  

Output :

Draw a rectangle using opencv

Draw a Circle :

cv2.circle(imageObjectName, (‘center_coordinates’), (‘circle_radius’), (‘color_in_bgr’), ‘stroke_thickness’)

Python3

   # Python3 program to draw circle 
# shape on solid image 
import numpy as np 
import cv2 
  
# Creating a black image with 3 
# channels RGB and unsigned int datatype 
img = np.zeros((400, 400, 3), dtype = "uint8") 
  
# Creating circle 
cv2.circle(img, (200, 200), 80, (255, 0, 0), 3) 
  
cv2.imshow('dark', img) 
  
# Allows us to see image 
# until closed forcefully 
cv2.waitKey(0) 
cv2.destroyAllWindows() 
 
  

Output :

Draw a circle using opencv

Writing text :

cv2.putText(imageObjectName, ‘TextContent’, (‘text_starting_point_coordinates’), ‘fontToBeUsed’, ‘font_size’, (‘text_color’, ‘text_thickness’, ‘line_type’)

Python

   # Python3 program to write  
# text on solid image 
import numpy as np 
import cv2 
  
# Creating a black image with 3 
# channels RGB and unsigned int datatype 
img = np.zeros((400, 400, 3), dtype = "uint8") 
  
# writing text 
font = cv2.FONT_HERSHEY_SIMPLEX 
cv2.putText(img, 'GeeksForGeeks', (50, 50), 
            font, 0.8, (0, 255, 0), 2, cv2.LINE_AA) 
  
cv2.imshow('dark', img) 
  
# Allows us to see image 
# until closed forcefully 
cv2.waitKey(0) 
cv2.destroyAllWindows() 
 
  

Output :

writing text using opencv

Applications of drawing shapes on images :

Drawing geometrical shapes can help us highlight the particular portions of an image.
Geometrical shapes like line can help us point or identify particular regions in image.
Writing text on certain regions of images can add description to that region.

Reference :
https://docs.opencv.org/2.4/modules/core/doc/drawing_functions.html

How to Detect Shapes in Images in Python using OpenCV?

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Draw geometric shapes on images using OpenCV

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Draw a line :

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Draw a rectangle :

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Draw a Circle :

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Writing text :

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