Creating your own contour in opencv using python
Solution 1
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)
Solution 2
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)
Solution 3
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!
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()
Shan
Updated on August 04, 2022Comments
-
Shan almost 2 years
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