Create numpy array (contour) to be used with opencv functions

Question

I'm new to python and I don't know how to create numpy array that may be used in opencv functions. I've got two vectors defined as follows:

X=np.array(x_list)
Y=np.array(y_list)

and the result is:

[ 250.78  250.23  249.67 ...,  251.89  251.34  250.78]
[ 251.89  251.89  252.45 ...,  248.56  248.56  251.89]

I want to create opencv contour to be used in ex. cv2.contourArea(contour). I read Checking contour area in opencv using python but cannot write my contour numpy array properly. What's the best way to do that?

Answer 1

Here's some example code, that first checks the dimensions of a contour calculated from a test image, and makes a test array and has success with that as well. I hope this help you!

import cv2
import numpy as np

img = cv2.imread('output6.png',0) #read in a test image
ret,thresh = cv2.threshold(img,127,255,0)
im2,contours,hierarchy = cv2.findContours(thresh, 1, 2)

cnt = contours[0]

print cnt.shape #this contour is a 3D numpy array
print cv2.contourArea(cnt) #the function prints out the area happily

#######Below is the bit you asked about

contour = np.array([[[0,0]], [[10,0]], [[10,10]], [[5,4]]]) #make a fake array
print cv2.contourArea(contour) #also compatible with function