如何使用查找轮廓open cv来增加边界框的大小？

import cv2

# 读取图像
image = cv2.imread('image.jpg')

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

# 二值化处理
ret, thresh = cv2.threshold(gray, 127, 255, cv2.THRESH_BINARY)

# 查找轮廓
contours, hierarchy = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

# 遍历轮廓
for contour in contours:
    # 计算边界框
    x, y, w, h = cv2.boundingRect(contour)
    
    # 增加边界框的大小
    x -= 10
    y -= 10
    w += 20
    h += 20
    
    # 绘制边界框
    cv2.rectangle(image, (x, y), (x + w, y + h), (0, 255, 0), 2)

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