如何在 python 中裁剪 PNG 图像？

Question

I have successfully managed to extract a skin patch from a facial image. However; for my task, I don't need the bottom eye and eyelash part. Is there a way to crop the following png image from the top at a slight angle? The resultant image should be in PNG format. I want to crop the following original image to the desired image:

Original Image

Desired Image

Answer 1

As long as you have the color values of the line of which you want to crop above of, you can do something like this:

import cv2
import numpy as np

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

for i, j in zip(*np.where(np.all(img == [0, 0, 253], 2))):
    img[:i, j] = 0

cv2.imshow("Image", img)
cv2.waitKey(0)

Output:

Explanation:

1. Import the necessary libraries:

import cv2
import numpy as np

2. Read in the image:

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

3. Loop though the indices of the image where the BGR value of the pixel at the indices is the BGR value of the line's color:

for i, j in zip(*np.where(np.all(img == [0, 0, 253], 2))):

4. Set all the pixels before the outer index at the inner index to black. If you were to visualize it it would be drawing black vertical lines one by one:

    img[:i, j] = 0

5. Show the resulting image:

cv2.imshow("Image", img)
cv2.waitKey(0)