How to remove multiple polygons using Opencv python

Question

Hi StackOverflow team,

I have an image and I want to remove many portions/parts from the image. I tried to use the below code taken from Cropping Concave polygon from Image using Opencv python

Assume I have this image . Also, I have multiple polygons (such as rectangular shapes or any form of a polygon) from the image achieved via lebelme annotation tool. So, I want to remove those shapes from the images or simply changing their pixels to white.

In other words, Labelme Tool will give you a dictionary file, where the dictionary has a key consisting of the points of each portion/polygon/shape)

Then the polygon points can be easily extracted from the dictionary file. After points are extracted, we can define our points by giving names (e.g a,b,s...h), and each one is in this multidimensional format "[[1526, 319], [1526, 376], [1593, 379], [1591, 324]]"

Here I thought of whitening each region. but whitening of multidimensional array seems to be unreliable.

import numpy as np
import cv2
import json

with open('ann1.json') as f:
    data = json.load(f)

#%%
a = data['shapes'][0]['points']; b = data['shapes'][1]['points']; c = data['shapes'][2]['points']; 
#%%
img = cv2.imread("lena.jpg")
pts = np.array(a) # Points

#%%
## (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)

Using Lena I have this output . But I need to go further and whiten other points/polygons, for example, the eyes.

As you can see my code can use only one polygon points. I tried appending two other polygon points in my case the two eyes and got .

By appending, I mean I added the multidimensional points (e.g. pts = np.array(a+b+c)).

In short, having an image is there a short way to remove these multiple polygons from the image (by keeping the dimensions of the image) using OpenCV and python.

Json File: https://drive.google.com/file/d/1UyOYUVMHpu2vBBEdR99bwrRX5xIfdOCa/view?usp=sharing

Can you please edit and add example images with the expected output? Currently, the description is not particularly clear. I think you may simply want to combine multiple masks, which a "bitwise or" should achieve. — alkasm
Do you mean you want to loop through every set of points and remove that polygon? — Shawn Mathew
Thanks, @AlexanderReynolds...I have edited the question. let me know if further editing is needed — Jama Hussein Mohamud
@ShawnMathew. thanks.. my intention is to remove every polygon by keeping the dimensions of the image. will looping through the points achieve that? — Jama Hussein Mohamud

Shawn Mathew Shawn Mathew · Accepted Answer · 2019-03-20T14:59:27

You'll need to use to loop to go through all the points in the JSON file. I've edited your code to reflect this.

import cv2
import json
import matplotlib.pyplot as plt
import numpy as np

img_path =r"/path/to/lena.png"
json_path = r"/path/to/lena.json"

with open(json_path) as f:
   data = json.load(f)


img = cv2.imread(img_path)

for idx in np.arange(len(data['shapes'])):
    if idx == 0:  #can remove this
        continue  #can remove this
    a = data['shapes'][idx]['points']
    pts = np.array(a) # Points

    ## (1) Crop the bounding rect
    rect = cv2.boundingRect(pts)
    print(rect)
    x,y,w,h = rect
    img[y:y+h, x:x+w] = (255, 255, 255)

    plt.imshow(img)
    plt.show()

Output: I ignored the first line, since it didn't visualize the results nicely. I took your lead and used rectangles instead of polygons. If you need polygons, you'll need to use something like cv2.drawContours() or cv2.polylines() or cv2.fillPoly() as is recommnded in the SO answer you have linked here, to achieve it.

How to remove multiple polygons using Opencv python

2 Answers