OpenCV，cv2.approxPolyDP()在封闭轮廓上绘制双线。

Question

我想从这个掩码中创建一些多边形:

图像1 - 掩膜

所以，我使用openCV findcontours()创建了这些轮廓:

图像2 - 轮廓

在创建多边形时，我得到了这些多边形:

图像3 - 多边形

你可以看到有些多边形使用双线绘制。如何防止这种情况发生？

查看我的代码:

import glob
from PIL import Image
import cv2
import numpy as np


# Let's load
image = cv2.imread(path + "BigOneEnhanced.tif") 

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

# Find Canny edges 
edged = cv2.Canny(gray, 30, 200) 

# Finding Contours 
contours, hierarchy = cv2.findContours(edged,  
    cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_TC89_L1) 

canvas = np.zeros(image.shape, np.uint8)

# creating polygons from contours

polygonelist = []

for cnt in contours:

    # define contour approx
    perimeter = cv2.arcLength(cnt,True)
    epsilon = 0.005*cv2.arcLength(cnt,True)
    approx = cv2.approxPolyDP(cnt,epsilon,True)


    polygonelist.append(approx)

cv2.drawContours(canvas, polygonelist, -1, (255, 255, 255), 3)


imgB = Image.fromarray(canvas)
imgB.save(path + "TEST4.png")

- B. Bram

Answer 1

问题的根源是Canny边缘检测：

应用边缘检测后，每个原始轮廓会得到两个轮廓——一个在边缘外面，一个在边缘里面（还有其他奇怪的东西）。

您可以通过不使用Canny来应用findContours来解决它。

以下是代码:

import glob
from PIL import Image
import cv2
import numpy as np

path = ''

# Let's load
#image = cv2.imread(path + "BigOneEnhanced.tif") 
image = cv2.imread("BigOneEnhanced.png") 

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

# Apply threshold (just in case gray is not binary image).
ret, thresh_gray = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY+cv2.THRESH_OTSU)

# Find Canny edges 
#edged = cv2.Canny(gray, 30, 200)

# Finding Contours cv2.CHAIN_APPROX_TC89_L1
#contours, hierarchy = cv2.findContours(edged, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

contours, hierarchy = cv2.findContours(thresh_gray, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

canvas = np.zeros(image.shape, np.uint8)

# creating polygons from contours
polygonelist = []

for cnt in contours:
    # define contour approx
    perimeter = cv2.arcLength(cnt, True)
    epsilon = 0.005*perimeter #0.005*cv2.arcLength(cnt, True)
    approx = cv2.approxPolyDP(cnt, epsilon, True)

    polygonelist.append(approx)

cv2.drawContours(canvas, polygonelist, -1, (255, 255, 255), 3)

imgB = Image.fromarray(canvas)
imgB.save(path + "TEST4.png")

结果：

- Rotem