将形状复制到空白画布（OpenCV、Python）

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('img.png')
imgray = cv2.cvtColor(im, cv2.COLOR_BGR2GRAY)
ret, thresh = cv2.threshold(imgray, 127, 255, 0)
image, contours, hierarchy = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

cnt = contours[4]
cnts = cv2.drawContours(im,[cnt],0,(255,0,0), -1)

cv2.imshow('i', im)
cv2.waitKey(0)

for a in cnt:
    print(a) #this contour is a 3D numpy array

源图片：

我使用这段代码来： 1.创建一个40x40像素的白色画布 2.使用Opencv函数找到数字（在本例中为5）的轮廓findContours.

我想要做的是将这个形状（请不要是边界框或矩形，蓝色形状）复制到画布中。

经过一些研究，我了解到 opencv 图像只是一个 numpy 数组。理论上，这个数组应该在新图像（我的白色画布......）中进行转换，然后使用数组内的值重建形状。我是对的 ？

有人知道该怎么做吗？在某些情况下，在数字周围创建边界框/矩形会导致不准确。请不要将此作为解决方案。我已经用至少 3-4 种不同的方式完成了这个过程，但结果还不够令人满意。

所以，期望的输出会是这样的..

Thanks.

For contours image

I think want something like

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 .

详细信息和说明都在代码中。

#!/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)