OpenCV findContours – What it is?

OpenCV findContours detects change in the image color and marked it as contour.

In this example using archery target face, findContours detects the outer circle, yellow circle, bullseye circle, logos on top left and bottom left.

In this case, findContours doesn’t detect the red circle contour.

The Original Image

The Image Gray

The Find Contours Image

Green color is the contours found on the image.

opencv findcontours on archery target face

The OpenCV Python Code

import os
import cv2 as cv
import numpy as np
import matplotlib.pyplot as plt


def findContours():
    root = os.getcwd()
    imgPath = os.path.join(root, 'images/target.jpg')
    img = cv.imread(imgPath)
    #change to GRAY to easily detect the contours
    imgGray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)

    ret, thresh = cv.threshold(imgGray, 127, 255, 0)
    contours, hierarchy = cv.findContours(thresh, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)


    imgContours = cv.drawContours(img, contours, -1, (0,255,0), 3)

    plt.figure()
    plt.subplot(121)
    plt.imshow(imgContours)
  
    plt.show()

    

if __name__ == '__main__':    
    print("Start")
    findContours()

import os

import cv2 as cv

import numpy as np

import matplotlib.pyplot as plt

def findContours():

root = os.getcwd()

imgPath = os.path.join(root, 'images/target.jpg')

img = cv.imread(imgPath)

#change to GRAY to easily detect the contours

imgGray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)

ret, thresh = cv.threshold(imgGray, 127, 255, 0)

contours, hierarchy = cv.findContours(thresh, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)

imgContours = cv.drawContours(img, contours, -1, (0,255,0), 3)

plt.figure()

plt.subplot(121)

plt.imshow(imgContours)

plt.show()

if __name__ == '__main__':

print("Start")

findContours()

Conclusion

findContours is an easy way to automatically detect an image shape or outline.

The Original Image

The Image Gray

The Find Contours Image

The OpenCV Python Code

Conclusion

References:

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