Only detect contours within a square

Question

Hello I have a code which draws me the outlines of shapes/objects which have 3 or 4 vertices. So far everything works. But now I want that only shapes/objects are recognized, which are in a square. I wanted to solve it in such a way that I create a square or a picture, in which a square is represented, with cv2.imread read and then with cv2.matchShapes check, how much the recognized contour agrees with the contour of the square. And if this match is good enough, corresponding objects/shapes within this square should be recognized.
Following is the code I have written so far:

import math
import cv2
import numpy as np
from graphics import *


cam = cv2.VideoCapture(0)
cam.set(cv2.CAP_PROP_FRAME_WIDTH, 1920)
cam.set(cv2.CAP_PROP_FRAME_HEIGHT, 1080)

rect = cv2.imread("Rectangle.png")
gray = cv2.cvtColor(rect, cv2.COLOR_BGR2GRAY)
rectcontour, _ = cv2.findContours(gray, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)


while True:
     _ , img = cam.read()
     img = cv2.resize(img, None, fx = 0.5, fy = 0.5, interpolation=cv2.INTER_AREA)
     gray1 = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
     #edges = cv2.Canny(gray1, 250, 300)
     _ , binary1 = cv2.threshold(gray1, 130, 255, cv2.THRESH_BINARY)
     inverted_binary1 = ~binary1
     contours1, _ = cv2.findContours(inverted_binary1, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

     a = 0
     for a in contours1:
          x = cv2.matchShapes(contours1[a], rectcontour[0], cv2.CONTOURS_MATCH_I1, 0.0)
          print(x)
          a = a + 1

     for contour in contours1:
          area = cv2.contourArea(contour)
          if  area > 100 and area < 20000:
               approx = cv2.approxPolyDP(contour, 0.06 * cv2.arcLength(contour, True), True)
               print(len(approx))

               if 2 < len(approx)  < 5:
                    moment = cv2.moments(contour)
                    cx = int(moment['m10'] / moment['m00'])
                    cy = int(moment['m01'] / moment['m00'])
                    #print(x, y)
                    print(cx, cy)
                    cv2.drawContours(img, [contour], -1, (0, 0, 255), 3)
                    n = approx.ravel()
                    print(n)
                    i = 0
                    for j in n:
                         if (i % 2 == 0):
                              x = n[i]
                              y = n[i + 1]

                              # String containing the co-ordinates.
                              string = str(x) + " " + str(y)


                              if (i == 0):
                                   # text on topmost co-ordinate.
                                   cv2.putText(img, string, (x, y),cv2.FONT_HERSHEY_COMPLEX_SMALL, 1, (255, 0, 0))
                              else:
                                   # text on remaining co-ordinates.
                                   cv2.putText(img, string, (x, y),cv2.FONT_HERSHEY_COMPLEX_SMALL, 1, (0, 255, 0))
                         i = i + 1




     cv2.imshow("schwarz, weiß", inverted_binary1)
     cv2.imshow('my webcam', img)

     if cv2.waitKey(1) & 0xFF == ord("q"):
          break

At the moment I get following error:

Traceback (most recent call last):
  File "C:\Users\Paul\PycharmProjects\Opencv	est3.py", line 27, in 
    x = cv2.matchShapes(contours1[a], rectcontour[0], cv2.CONTOURS_MATCH_I1, 0.0)
TypeError: only integer scalar arrays can be converted to a scalar index
[ WARN:0] global D:\a\opencv-python\opencv-python\opencv\modules\videoio\src\cap_msmf.cpp (438) `anonymous-namespace'::SourceReaderCB::~SourceReaderCB terminating async callback

And I dont exactly know how I can fix that.

The square image I am using: enter image description here

And another Picture of the shape I actually want to detect: enter image description here

Only detect contours within a square

0 Answers