Draw geometric shapes on images using OpenCV

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

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# 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
# untill closed forcefully
cv2.waitKey(0)
cv2.destroyAllWindows()

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Output :

 
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’)

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# 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
# untill closed forcefully
cv2.waitKey(0)
cv2.destroyAllWindows()

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Output :

 

Draw a rectangle :

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

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# 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
# untill closed forcefully
cv2.waitKey(0)
cv2.destroyAllWindows()

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Output :

 

Draw a Circle :

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

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# 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
# untill closed forcefully
cv2.waitKey(0)
cv2.destroyAllWindows()

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Output :

 

Writing text :

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

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# 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
# untill closed forcefully
cv2.waitKey(0)
cv2.destroyAllWindows()

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Output :


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



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