Draw circle around imperfect circular objects

Question

I have this image of an eye where I want to get the center of the pupil: Original Image

I applied adaptive threshold as well as laplacian to the image using this code:

import cv2
import numpy as np
from matplotlib import pyplot as plt

img = cv2.imread('C:\Users\User\Documents\module4\input\left.jpg',0)
image = cv2.medianBlur(img,5)

th = cv2.adaptiveThreshold(image,255,cv2.ADAPTIVE_THRESH_MEAN_C, 
cv2.THRESH_BINARY,11,2)

laplacian = cv2.Laplacian(th,cv2.CV_64F)

cv2.imshow('output', laplacian)
cv2.imwrite('C:\Users\User\Documents\module4\output\output.jpg', laplacian)

cv2.waitKey(0)
cv2.destroyAllWindows

and the resulting image looks like this: Resulting image by applying adaptive threshold

I want to draw a circle around the smaller inner circle and get its center. I've tried using contours and circular hough transform but it does not correctly detect any circles in the image.

Here is my code for Circular Hough Transform:

import cv2
import numpy as np
from matplotlib import pyplot as plt

img = cv2.imread('C:\Users\User\Documents\module4\output\output.jpg',0)

circles = cv2.HoughCircles(img,cv2.HOUGH_GRADIENT,1,20,param1=50,param2=30,minRadius=0,maxRadius=0)

circles = np.uint16(np.around(circles))
for i in circles[0,:]:
    # draw the outer circle
    cv2.circle(img,(i[0],i[1]),i[2],(255,255,0),2)
    # draw the center of the circle
    cv2.circle(img,(i[0],i[1]),2,(255,0,255),3)

cv2.imshow('detected circles',img)
cv2.waitKey(0)
cv2.destroyAllWindows()

And here is the code for applying contour:

import cv2
import numpy as np

img = cv2.imread('C:\Users\User\Documents\module4\output\output.jpg',0)

_, contours,hierarchy = cv2.findContours(img, 1, 2)

cnt = contours[0]

(x,y),radius = cv2.minEnclosingCircle(cnt)
center = (int(x),int(y))
radius = int(radius)
img = cv2.circle(img,center,radius,(0,255,255),2)

cv2.imshow('contour', img)

cv2.waitKey(0)
cv2.destroyAllWindows()

The resulting image of this code exactly looks like the image wherein I applied adaptive threshold. I would really appreciate it if anyone can help me solve my problem. I've been stuck with this for a while now. Also, if any of you guys can suggest a better way to detect the center of the pupil besides this method, I would also really appreciate it.

Answer 1

try to apply edge detection instead of shareholding after filtering of original image and then apply hough circle