How can i know if a contour is open or closed in opencv?

Question

How can i know if a contour taken from 'find contour' function is open or closed in opencv?

UPDATE

I tried to apply isContourConvex to this image: https://docs.google.com/file/d/0ByS6Z5WRz-h2RXdzVGtXUTlPSGc/edit?usp=sharing

i extractes contour with greatest area and return false. I change, maybe, contour extraction, dilating?

nomeimg = 'Riscalate2/JPEG/e (5).jpg'

img = cv2.imread(nomeimg)

gray = cv2.imread(nomeimg,0)#convert grayscale adn binarize

element = cv2.getStructuringElement(cv2.MORPH_CROSS,(6,6)) 
graydilate = cv2.erode(gray, element) #imgbnbin

cv2.imshow('image',graydilate)
cv2.waitKey(0)

ret,thresh = cv2.threshold(graydilate,127,255,cv2.THRESH_BINARY_INV)   # binarize

imgbnbin = thresh
cv2.imshow('bn',thresh)
cv2.waitKey()

#element = cv2.getStructuringElement(cv2.MORPH_CROSS,(2,2))
#element = np.ones((11,11),'uint8')


contours, hierarchy = cv2.findContours(imgbnbin, cv2.RETR_TREE ,cv2.CHAIN_APPROX_SIMPLE)
print(len(contours))


# Take only biggest contour basing on area
Areacontours = list()
calcarea = 0.0
unicocnt = 0.0
for i in range (0, len(contours)):
    area = cv2.contourArea(contours[i])
    #print("area")
    #print(area)
    if (area > 90 ):  #con 90 trova i segni e togli puntini
        if (calcarea<area):
            calcarea = area
            unicocnt = contours[i]


convex = cv2.isContourConvex(unicocnt)
print("convex")
print(convex)

Answer 1

You're looking for the terms concave (like a C) vs convex (like an O) contours.

And guess what, there is a method to check for convexity:

cv2.isContourConvex(contour)