How to add border around an image in opencv python

Question

If I have an image like below, how can I add border all around the image such that the overall height and width of the final image increases but the height and width of the original image stays as-is in the middle.

How about [cv2.copyMakeBorder](http://docs.opencv.org/2.4/modules/imgproc/doc/filtering.html#void%20copyMakeBorder%28InputArray%20src,%20OutputArray%20dst,%20int%20top,%20int%20bottom,%20int%20left,%20int%20right,%20int%20borderType,%20const%20Scalar&%20value%29) ? — Dan Mašek, Mar 28 '16 at 03:49
By the way, opencv official documentation provides a [tutorial](https://docs.opencv.org/master/dc/da3/tutorial_copyMakeBorder.html) how to append a border to am image using cv2.copyMakeBorder. — Evgeny Bobkin, Jun 05 '19 at 09:58

score 53 · Accepted Answer · edited Mar 01 '23 at 13:03

The following code adds a constant border of size 10 pixels to all four sides of your original image.

For the colour, I have assumed that you want to use the average gray value of the background, which I have calculated from the mean value of bottom two lines of your image. Sorry, somewhat hard coded, but shows the general how-to and can be adapted to your needs.

If you leave border_size values for bottom and right at 0, you even get a symmetric border.

Other values for BORDER_TYPE are possible, such as BORDER_DEFAULT, BORDER_REPLICATE, BORDER_WRAP.

For more details cf: http://docs.opencv.org/trunk/d3/df2/tutorial_py_basic_ops.html#gsc.tab=0

import numpy as np
import cv2

im = cv2.imread('image.jpg')
row, col = im.shape[:2]
bottom = im[row-2:row, 0:col]
mean = cv2.mean(bottom)[0]

border_size = 10
border = cv2.copyMakeBorder(
    im,
    top=border_size,
    bottom=border_size,
    left=border_size,
    right=border_size,
    borderType=cv2.BORDER_CONSTANT,
    value=[mean, mean, mean]
)

cv2.imshow('image', im)
cv2.imshow('bottom', bottom)
cv2.imshow('border', border)
cv2.waitKey(0)
cv2.destroyAllWindows()

Using the tutorial I thought that the value for Red (confusingly labelled Blue) should be [255, 0, 0]. But actually it was [1.0, 0, 0] with floats as the image value colours. — hum3, May 25 '17 at 11:56

score 20 · Answer 2 · edited Mar 12 '18 at 09:37

20

Answer in one line

outputImage = cv2.copyMakeBorder(
                 inputImage, 
                 topBorderWidth, 
                 bottomBorderWidth, 
                 leftBorderWidth, 
                 rightBorderWidth, 
                 cv2.BORDER_CONSTANT, 
                 value=color of border
              )

edited Mar 12 '18 at 09:37

JustBaron

2,319
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answered Mar 12 '18 at 09:08

Ishara Madhawa

3,549
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score 16 · Answer 3 · edited Jun 05 '19 at 09:53

16

Try This:

import cv2
import numpy as np     

img=cv2.imread("img_src.jpg")
h,w=img.shape[0:2]

base_size=h+20,w+20,3
# make a 3 channel image for base which is slightly larger than target img
base=np.zeros(base_size,dtype=np.uint8)
cv2.rectangle(base,(0,0),(w+20,h+20),(255,255,255),30) # really thick white rectangle
base[10:h+10,10:w+10]=img # this works

edited Jun 05 '19 at 09:53

Evgeny Bobkin

4,092
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answered Mar 31 '16 at 10:31

Saransh Kejriwal

2,467
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score 8 · Answer 4 · answered Aug 24 '20 at 11:11

8

Add border using openCV

import cv2
white = [255,255,255]
img1 = cv2.imread('input.png')
constant= cv2.copyMakeBorder(img1,20,20,20,20,cv2.BORDER_CONSTANT,value=white)
cv2.imwrite('output.png',constant)

answered Aug 24 '20 at 11:11

Eliyaz KL

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How to add border around an image in opencv python

4 Answers4

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