How to fill a polygon using opencv python

Question

I would like to fill these polygon with white color and this operation is repeated through a loop over the whole image so I would like to know the syntax and function which can be used to perform this operation using opencv in python This is my input image

alist=[]
img = cv2.imread('closing2.jpg',cv2.IMREAD_GRAYSCALE)
imo = cv2.imread('closing2.jpg',cv2.IMREAD_GRAYSCALE)
imr = cv2.imread('closing2.jpg',cv2.IMREAD_GRAYSCALE)*0
imac = imr
height , width  = imo.shape[:2]
a,im = cv2.threshold(img,200,255,cv2.THRESH_BINARY)
# i=100
# p=[i,i]
points = []
for j in range(0,1000,50):
    for i in range(0,1000,50):
        p=[i,j]
        poly = raypoly(im,p,5)
        st = metrics(p,poly)

        polyc=raypolyLimit(im,p,st,30)
        # print(polyc)
        # print(len(polyc))
        # for m in range(len(polyc)):
        #     point = polyc[m]
        #     cv2.fillConvexPoly(im, point, 255)
        plotpoly(polyc,imr)

        plotpolypoints(polyc,imr,255,1)
        # plotray(im,p,imr)

        am = polyArea(polyc)
        # print(am)
        if am > 5:
            alist.append(am)
            # img[(i-5):(i+5),(j-5):(j+5)]=150
            # plt.imshow(imf)
            # plt.show()
        imo = im * 0
        plotpoly(polyc,imo)
        plotpoly(polyc, im)
        # plotArea(polyc,imo)
        imf = imo*1000 +im
        a,imf = cv2.threshold(imf,100.0,255.0,cv2.THRESH_BINARY)
        cv2.imshow('Frame_1', imr)
        cv2.imshow('Frame_3', imo)
        cv2.imshow('Frame_4', imf)
        cv2.imshow('Frame_5', im)
        cv2.waitKey(1)

I used the following function and the result as follows:

cv2.floodFill(imo,None,(i,j),255)

But my problem is that it gives a white flash for the whole image after certain number of polygons and I don't know how to fix it .

Answer 1

You can use cv2.drawContours() to fill in a contour. From the docs, if the thickness parameter is negative (thickness=CV_FILLED or thickness=-1) then the contours will be filled. For instance, to fill in a contour with white

cv2.drawContours(image, [c], -1, (255,255,255), -1)

---

So the idea is to find the desired contour using cv2.findContours() then fill it in using cv2.drawContours(). For your image:

import cv2

image = cv2.imread('1.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
thresh = cv2.threshold(gray, 120, 255, cv2.THRESH_BINARY)[1]
cnts = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
cnts = cnts[0] if len(cnts) == 2 else cnts[1]

for c in cnts:
    cv2.drawContours(image, [c], -1, (255,255,255), -1)

cv2.imshow('image', image)
cv2.waitKey()