Creating your own contour in opencv using python

Question

I have a set of boundary points of an object.

I want to draw it using opencv as contour.

I have no idea that how to convert my points to contour representation.

Answer 1

A contour is simply a curve joining all continuous points so to create your own contour, you can create a np.array() with your (x,y) points in clockwise order

points = np.array([[25,25], [70,10], [150,50], [250,250], [100,350]])

That's it!

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There are two methods to draw the contour onto an image depending on what you need:

Contour outline

If you only need the contour outline, use cv2.drawContours()

cv2.drawContours(image,[points],0,(0,0,0),2)

Filled contour

To get a filled contour, you can either use cv2.fillPoly() or cv2.drawContours() with thickness=-1

cv2.fillPoly(image, [points], [0,0,0]) # OR
# cv2.drawContours(image,[points],0,(0,0,0),-1)

Full example code for completeness

import cv2
import numpy as np

# Create blank white image
image = np.ones((400,400), dtype=np.uint8) * 255

# List of (x,y) points in clockwise order
points = np.array([[25,25], [70,10], [150,50], [250,250], [100,350]])

# Draw points onto image
cv2.drawContours(image,[points],0,(0,0,0),2)

# Fill points onto image
# cv2.fillPoly(image, [points], [0,0,0])

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