用NumPy填充图像会全黑

Question

I use NumPy to create a new 2D array with 0 on the border and the array of the original image inside. I print the new array, it's what I expect. But when I plot it, it's all black.

I tried for-loop and NumPy, it's useless.

import cv2
import numpy as np

path = 'test.jpg'
img = cv2.imread(path,0)

print(img)
height,width = img.shape       # 440 * 455

new_arr = np.zeros((height+2,width+2), dtype = int)

#for i in range(height):
#   for j in range(width):
#      new_arr[i+1][j+1] = img[i][j]

new_arr[1:height+1,1:width+1] = img
print(new_arr)


cv2.imshow('new image',new_arr)
cv2.waitKey(0)
cv2.destroyAllWindows()

The original image is here:

I expect an image with black border (just 1 pixel), and the inside is the original image to do median filtering, but the actual output is a black image.

Answer 1

Not sure how you are getting black image, as your code should throw an error. You need to set dtype value in proper namespace ( np. ) and the value should be uint8 :

import cv2
import numpy as np

path = 'test.png'
img = cv2.imread(path,0)

height,width = img.shape

new_arr = np.zeros((height+2,width+2), dtype = np.uint8)

new_arr[1:height+1,1:width+1] = img
print(new_arr)

cv2.imshow('new image',new_arr)
cv2.waitKey(0)
cv2.destroyAllWindows()

Please note that the image you have given is png , not jpg . Code tested on that image.