如何使用opencv检测图像中的矩形(白板)？

import cv2
import numpy as np

image = cv2.imread('image.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
blur = cv2.GaussianBlur(gray, (5, 5), 0)

edges = cv2.Canny(blur, 50, 150)

contours, _ = cv2.findContours(edges, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

for contour in contours:
    perimeter = cv2.arcLength(contour, True)
    approx = cv2.approxPolyDP(contour, 0.02 * perimeter, True)
    
    if len(approx) == 4:
        x, y, w, h = cv2.boundingRect(approx)
        aspect_ratio = float(w) / h
        
        if aspect_ratio >= 0.9 and aspect_ratio <= 1.1:
            cv2.rectangle(image, (x, y), (x + w, y + h), (0, 255, 0), 2)

cv2.imshow('Detected Rectangles', image)
cv2.waitKey(0)
cv2.destroyAllWindows()