opencv 21 detect geometric shapes

original image

apply threshold

draw contour and text

#main.py

import numpy as np

import cv2

img = cv2.imread('assets/geometric shapes.jpg')

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

_, thresh = cv2.threshold(gray, 70, 80, cv2.THRESH_BINARY)

contours, _ = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)

for contour in contours:

    if cv2.contourArea(contour) < 2000:

        continue

    #polyDP (contour, accuracy, shape closed?)

    approx = cv2.approxPolyDP(contour, 0.01 * cv2.arcLength(contour, True), True)

    cv2.drawContours(img, [approx], 0, (255, 255 , 255), 1)

    #print(approx)

    x = approx.ravel()[0]

    y = approx.ravel()[1] - 15

    if len(approx) == 3:

        cv2.putText(img, 'triangle', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

    elif len(approx) == 4:

        x, y, w, h = cv2.boundingRect(approx)

        aspectRatio = float(w)/h

        if aspectRatio >= 0.95 and aspectRatio <= 1.05:

            cv2.putText(img, 'square', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

        else:

            cv2.putText(img, 'rectangle', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

    elif len(approx) == 5:

        cv2.putText(img, 'pentagon', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

    elif len(approx) == 6:

        cv2.putText(img, 'hexagon', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

    elif len(approx) == 7:

        cv2.putText(img, 'heptagon', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

    elif len(approx) == 8:

        cv2.putText(img, 'octagon', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

    elif len(approx) == 9:

        cv2.putText(img, 'nonagon', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

    elif len(approx) == 10:

        cv2.putText(img, 'star', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

    else:

        cv2.putText(img, 'circle', (x, y), cv2.FONT_HERSHEY_COMPLEX, 0.5, (255, 255, 255))

cv2.imshow('threshold', thresh)

cv2.imshow('contours', img)

cv2.waitKey(0)

cv2.destroyAllWindows()

reference:

https://www.youtube.com/watch?v=mVWQNeY1Pb4&list=PLS1QulWo1RIa7D1O6skqDQ-JZ1GGHKK-K&index=29