Sunday, 17 July 2016

TUT8: Basic Drawing - Circle

In this tutorial, we are going to see how can we draw a circle using Python, OpenCV and Numpy.


import cv2                                          #Line 1
import numpy as np                                  #Line 2

img=np.zeros((500,500,3), np.uint8)                 #Line 3, (200,200), 150, (255, 0, 0), 2)     #Line 4

cv2.imshow('img',img)                               #Line 5

cv2.waitKey(0)                                      #Line 6
cv2.destroyAllWindows()                             #Line 7

Line 1-2: Import necessary packages

Line 3: Create a blank image using np.zeros().   #see previous tutorial to understand how it works.

Line 4: Use function, (x, y), r, color, thickness ) to create a circle on the blank                        image
  • image is the name of the blank image on which we will draw our circle
  • (x,y) is the center of the circle. 
  • r is the radius of the circle
  • color defined as (B, G, R). B, G, R represent the intensity of blue, green and red  color in your circle. Max intensity is 255 for each color. You can experiment with other value too for different color circles.
  • thickness represents the thickness of the circumference line of the circle.
Line 5: Display the picture using imshow() function. 

Line 6: Hold screen infinitely until user closes it.

Line 7: Close any open windows. 


So that's it for this tutorial. Hope you are learning to use OpenCV with Python and Numpy. See you in my next tutorial where we will learn to draw more complex drawings which will involve use of both circle and line.

Any queries , please ask in comments section below. :)

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