Python OpenCV 找到最大轮廓

Question

I have a problem while looking for biggest contour. I'm using image after canny edge detection:

Then I'm using

contours, hierarchy = cv2.findContours(edges,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

to find contours:

Next step is to find the biggest contour... I've tried:

contour = max(contours, key = cv2.contourArea)

but this give me something like:

Any ideas how to fix this? Thanks!

Code:

import cv2
image = cv2.imread('TEST_1.png')

gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

gaussian = cv2.GaussianBlur(gray,(3,3),cv2.BORDER_DEFAULT)
edges = cv2.Canny(gaussian,100,200)

contours, hierarchy = cv2.findContours(edges,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
contour = max(contours, key = cv2.contourArea)

contourImg = cv2.drawContours(image, contour, -1, (0,255,0), 3)
cv2.imshow("Contours", contourImg)

cv2.waitKey(0)
cv2.destroyAllWindows()

Also, contour area for this dot is 109 and for my biggest contour is 3.5

Answer 1

Apparently it seems like some contours are not closed. Using length as criterion rather than area in this case worked for me.

import cv2
image = cv2.imread('TEST_1.png')

gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

gaussian = cv2.GaussianBlur(gray,(3,3),cv2.BORDER_DEFAULT)
edges = cv2.Canny(gaussian,100,200)

contours, hierarchy = cv2.findContours(edges,cv2.RETR_TREE,cv2.CHAIN_APPROX_NONE)
contour = max(contours, key = len)

contourImg = cv2.drawContours(image, contour, -1, (0,255,0), 3)
cv2.imshow("Contours", contourImg)

cv2.waitKey(0)
cv2.destroyAllWindows()

I also changed the method in findContours from cv2.CHAIN_APPROX_SIMPLE to cv2.CHAIN_APPROX_NONE. Alternately, you try fixing the problem by changing the limit values in cv2.Canny() and using cv2.RETR_EXTERNAL.