如何在此PYTHON文件中将形状从圆形更改为方形

import cv2
import numpy as np

# 加载图像
image = cv2.imread('image.jpg')

# 转换为灰度图像
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

# 进行边缘检测
edges = cv2.Canny(gray, 50, 150)

# 查找轮廓
contours, _ = cv2.findContours(edges, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

# 遍历所有轮廓
for contour in contours:
    # 近似为多边形
    approx = cv2.approxPolyDP(contour, 0.04 * cv2.arcLength(contour, True), True)
    
    # 如果近似的多边形有四个顶点，则认为是方形
    if len(approx) == 4:
        # 绘制方形轮廓
        cv2.drawContours(image, [approx], 0, (0, 255, 0), 2)

# 显示结果图像
cv2.imshow('Result', image)
cv2.waitKey(0)
cv2.destroyAllWindows()