openn Cv2绘图轮廓

Question

我正在运行此代码，但出现错误

cv2.drawContours(image,contours,-1,(0,255,0),3)

error: OpenCV(3.4.3) D:\Build\OpenCV\opencv-3.4.3\modules\imgproc\src\drawing.cpp:2511: error: (-215:Assertion failed) npoints > 0 in function 'cv::drawContours'

---

import cv2
import numpy as np

image=cv2.imread("C:/Users/AnushkaGupta/Desktop/image database/input1.jpg")
cv2.imshow("original image",image)
cv2.waitKey(0)

gray=cv2.cvtColor(image,cv2.COLOR_BGR2GRAY)

edged=cv2.Canny(gray,30,200)
cv2.imshow("Canny Edges",edged)
cv2.waitKey(0)

contours,hierarchy, _=cv2.findContours(edged,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE)
cv2.imshow("canny Edges After Contouring",edged)
cv2.waitKey(0)

print("Number of Contours found ="+str(len(contours)))



cv2.drawContours(image,contours,-1,(0,255,0),3)

cv2.imshow("Contours",image)
cv2.waitKey(0)
cv2.destroyAllWindows()

Answer 1

当您收集findContours（）的输出时，顺序应如下：

image, contours, hierarchy = cv2.findContours(...)

在您的特定情况下，您应该写（我省略了imshow步骤）：

import cv2
import numpy as np

image = cv2.imread("./input1.jpg")

gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

edged = cv2.Canny(gray, 30, 200)

_, contours, hierarchy = cv2.findContours(edged, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

print(f"Number of Contours found = {len(contours)}")

cv2.drawContours(image, contours, -1, (0,255,0), 3)