使用OpenCV转换后的背景减少

Question

我有以下输入图像：

我已经编写了以下代码，以在每个字符上添加框式批注：

import cv2
import numpy as np
import csv
import sys

img = cv2.imread('gray_image.png')

(h, w) = img.shape[:2]
image_size = h*w
mser = cv2.MSER_create()
mser.setMaxArea(int(image_size/2))
mser.setMinArea(10)

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY) #Converting to GrayScale
_, bw = cv2.threshold(gray, 0.0, 255.0, cv2.THRESH_BINARY | cv2.THRESH_OTSU)

regions, rects = mser.detectRegions(bw)

# With the rects you can e.g. crop the letters
for (x, y, w, h) in rects:
    cv2.rectangle(img, (x, y), (x+w, y+h), color=(255, 0, 255), thickness=1)

cv2.imwrite('white_bg_new.jpg', img)
cv2.waitKey(0)
cv2.destroyAllWindows()

此代码的输出：

我想提取出框内所有的项目，并在框外应用白色背景。我该怎么办？