如何在opencv python中将颜色更改为图像的特定部分？

Question

I have an image of front facing man in which:

1) I used facial landmark detection to detect the chin point.

2) Add some specific value to lower its y-coordinate value.

3) Find out the width of image.

4) Draw an line through the point.

Now, what I want to do is change the color to portion of image below the yellow line to white color, so that I could have a whole separated head only. How to do that?

Code I have done till now:

import cv2
import numpy as np
import dlib

img1 = cv2.imread('Test.jpg')

#Facial Landmark Detection
predictor_path = "C:\\Users\\G7K4\\Desktop\\BackEnd_New\\01 HeadSwap\\shape_predictor_68_face_landmarks.dat"
detector = dlib.get_frontal_face_detector()
predictor = dlib.shape_predictor(predictor_path) 

img2 = detector(img1)

for k, d in enumerate(img2):
    shape = predictor(img1, d)

vec = np.empty([68, 2], dtype = int)
for b in range(68):
    vec[b][0] = shape.part(b).x
    vec[b][1] = shape.part(b).y

SampleHead_chinPoint = (vec[8,0], vec[8,1])
print(SampleHead_chinPoint )
a = SampleHead_chinPoint[0]
b = SampleHead_chinPoint[1]
c = b + 25
cv2.circle(img1, (a, c), 5, (0,0,255), -1)
cv2.imshow("Pointed", img1)
cv2.waitKey(0)

width = img1.shape[1]
cv2.line(img1, (0,c), (width, c), (0, 255, 255), 2)
cv2.imshow("Lined", img1)
cv2.waitKey(0)
cv2.destroyAllWindows()

Images:

Original Image:

Output 1:

Output 2:

Answer 1

Assumpt you have the chin point.

import cv2

img = cv2.imread("2.png")

chin_point = (370,230)

img[chin_point[0]:,:] = [255,255,255]

cv2.imshow("img", img)    

cv2.waitKey()
cv2.destroyAllWindows()