OpenCV:Example:Blending

import cv2

image = cv2.imread('test.jpg')
overlay = image.copy()

x, y, w, h = 10, 10, 10, 10  # Rectangle parameters
cv2.rectangle(overlay, (x, y), (x+w, y+h), (0, 200, 0), -1)  # A filled rectangle

alpha = 0.4  # Transparency factor.

# Following line overlays transparent rectangle over the image
image_new = cv2.addWeighted(overlay, alpha, image, 1 - alpha, 0)

## Crop and paste polygon image

import numpy as np
import cv2

img = cv2.imread("test.png")
pts = np.array([[10,150],[150,100],[300,150],[350,100],[310,20],[35,10]])

## (1) Crop the bounding rect
rect = cv2.boundingRect(pts)
x,y,w,h = rect
croped = img[y:y+h, x:x+w].copy()

## (2) make mask
pts = pts - pts.min(axis=0)

mask = np.zeros(croped.shape[:2], np.uint8)
cv2.drawContours(mask, [pts], -1, (255, 255, 255), -1, cv2.LINE_AA)

## (3) do bit-op
dst = cv2.bitwise_and(croped, croped, mask=mask)

## (4) add the white background
bg = np.ones_like(croped, np.uint8)*255
cv2.bitwise_not(bg,bg, mask=mask)
dst2 = bg+ dst


cv2.imwrite("croped.png", croped)
cv2.imwrite("mask.png", mask)
cv2.imwrite("dst.png", dst)
cv2.imwrite("dst2.png", dst2)