Set white color outside boundingBox (Python, OpenCV)

Question

I have this image:

(or this..)

How can I set to white all the area outside the boundingBox'es ?

I would like to obtain this result:

Thanks

Answer 1

As mentioned in the comments if you have the positions of the ROIs, you can use them to paste them on the an image with white background having the same shape as the original.

import cv2
import numpy as np

image = cv2.imread(r'C:\Users\Desktop\rus.png')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
white_bg = 255*np.ones_like(image)

ret, thresh = cv2.threshold(gray, 60, 255, cv2.THRESH_BINARY_INV)
blur = cv2.medianBlur(thresh, 1)
kernel = np.ones((10, 20), np.uint8)
img_dilation = cv2.dilate(blur, kernel, iterations=1)
im2, ctrs, hier = cv2.findContours(img_dilation.copy(), cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

sorted_ctrs = sorted(ctrs, key=lambda ctr: cv2.boundingRect(ctr)[0])
for i, ctr in enumerate(sorted_ctrs):
    # Get bounding box
    x, y, w, h = cv2.boundingRect(ctr)
    roi = image[y:y + h, x:x + w]
    if (h > 50 and w > 50) and h < 200:

        cv2.rectangle(image, (x, y), (x + w, y + h), (255, 255, 255), 1)        
        cv2.imshow('{}.png'.format(i), roi)

        #--- paste ROIs on image with white background 
        white_bg[y:y+h, x:x+w] = roi

cv2.imshow('white_bg_new', white_bg)
cv2.waitKey(0)
cv2.destroyAllWindows() 

The result: