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.

To the same contour representation which is obtained by following call

  contours,_ = cv2.findContours(image,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

Any ideas?

Thanks

1
8
1/4/2013 5:02:50 PM

Accepted Answer

By looking at the format of the contours I would think something like this should be sufficient:

contours = [numpy.array([[1,1],[10,50],[50,50]], dtype=numpy.int32) , numpy.array([[99,99],[99,60],[60,99]], dtype=numpy.int32)]

This small program gives an running example:

import numpy
import cv2

contours = [numpy.array([[1,1],[10,50],[50,50]], dtype=numpy.int32) , numpy.array([[99,99],[99,60],[60,99]], dtype=numpy.int32)]

drawing = numpy.zeros([100, 100],numpy.uint8)
for cnt in contours:
    cv2.drawContours(drawing,[cnt],0,(255,255,255),2)

cv2.imshow('output',drawing)
cv2.waitKey(0)
13
1/4/2013 5:27:19 PM

To create your own contour from a python list of points L

L=[[x1,y1],[x2,y2],[x3,y3],[x4,y4],[x5,y5],[x6,y6],[x7,y7],[x8,y8],[x9,y9],...[xn,yn]]

Create a numpy array ctr from L, reshape it and force its type

ctr = numpy.array(L).reshape((-1,1,2)).astype(numpy.int32)

ctr is our new countour, let's draw it on an existing image

cv2.drawContours(image,[ctr],0,(255,255,255),1)

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