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Real-Time Edge Detection using OpenCV in Python | Canny edge detection method

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The objective of the program given is to perform edge detection of images in real-time. In this article, the popular canny edge detection algorithm is used to detect a wide range of edges in images. OpenCV has in-built function cv2.Canny() which takes our input image as first argument and its aperture size(min value and max value) as last two arguments. This is a simple example of how to detect edges in Python. Steps to download the requirements below:

  1. Download Python 2.7.x version, numpy and OpenCV 2.7.x or 3.1.0 version.Check if your Windows either 32 bit or 64 bit is compatible and install accordingly.
  2. Make sure that numpy is running in your python then try to install opencv.



# OpenCV program to perform Edge detection in real time
# import libraries of python OpenCV 
# where its functionality resides
import cv2 
# np is an alias pointing to numpy library
import numpy as np
# capture frames from a camera
cap = cv2.VideoCapture(0)
# loop runs if capturing has been initialized
    # reads frames from a camera
    ret, frame =
    # converting BGR to HSV
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
    # define range of red color in HSV
    lower_red = np.array([30,150,50])
    upper_red = np.array([255,255,180])
    # create a red HSV colour boundary and 
    # threshold HSV image
    mask = cv2.inRange(hsv, lower_red, upper_red)
    # Bitwise-AND mask and original image
    res = cv2.bitwise_and(frame,frame, mask= mask)
    # Display an original image
    # finds edges in the input image and
    # marks them in the output map edges
    edges = cv2.Canny(frame,100,200)
    # Display edges in a frame
    # Wait for Esc key to stop
    k = cv2.waitKey(5) & 0xFF
    if k == 27:
# Close the window
# De-allocate any associated memory usage

Output: output References:


This article is contributed by Afzal Ansari. If you like GeeksforGeeks and would like to contribute, you can also write an article using or mail your article to See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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Last Updated : 04 Jan, 2023
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