Copy shape to blank canvas (OpenCV, Python)

Question

import numpy as np
import cv2

blank_image = np.zeros((40,40,3), np.uint8)
blank_image.fill(255)

#cv2.imshow(\'i\', blank_image)
#cv2.waitKey(0)

im = cv2.imread(\'         


        

Answer 1

For contours image

I think want something like

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For opened number such as 1, 2, 5 , it is easy to do: Crop from the whole image, or draw on new image. For closed number such as 0, 6, 8, 9, more steps are needed. Here is example for 5, you will get .

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Details and description are in the code.

#!/usr/bin/python3
# 2018.01.14 09:48:15 CST
# 2018.01.14 11:39:03 CST

import numpy as np
import cv2

im = cv2.imread('test.png')
imgray = cv2.cvtColor(im, cv2.COLOR_BGR2GRAY)
ret, thresh = cv2.threshold(imgray, 127, 255, 0)
contours = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)[-2]


## this contour is a 3D numpy array
cnt = contours[4]
res = cv2.drawContours(im,[cnt],0,(255,0,0), -1)
cv2.imwrite("contours.png", res)

## Method 1: crop the region
x,y,w,h = cv2.boundingRect(cnt)
croped = res[y:y+h, x:x+w]
cv2.imwrite("croped.png", croped)

## Method 2: draw on blank
# get the 0-indexed coords
offset = cnt.min(axis=0)
cnt = cnt - cnt.min(axis=0)
max_xy = cnt.max(axis=0) + 1
w,h = max_xy[0][0], max_xy[0][1]
# draw on blank
canvas = np.ones((h,w,3), np.uint8)*255
cv2.drawContours(canvas, [cnt], -1, (255,0,0), -1)
cv2.imwrite("canvas.png", canvas)