OpenCV, cv2.approxPolyDP() 在闭合轮廓上绘制双线答案

【问题标题】：OpenCV, cv2.approxPolyDP() Draws double lines on closed contourOpenCV, cv2.approxPolyDP() 在闭合轮廓上绘制双线
【发布时间】：2020-06-24 12:12:36
【问题描述】：

我想用这个蒙版创建一些多边形：

图片 1 - 面具

所以我用 openCV findcontours() 创建了这些轮廓：

图像 2 - 轮廓

创建多边形时，我得到了这些多边形：

图像 3 - 多边形

如您所见，一些多边形是使用双线绘制的。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")

【问题讨论】：

标签： python opencv polygon mask opencv-contour

【解决方案1】：

问题来源是Canny edges检测：

应用边缘检测后，您会为每个原始轮廓获得两个轮廓 - 一个在边缘外，一个在边缘内（以及其他奇怪的东西）。

您可以通过应用findContours 而不使用Canny 来解决它。

代码如下：

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：

【讨论】：

【解决方案2】：

opencv findcontour 建议根据 opencv-tutorials 组合 cv2.canny，使用阈值图像代替它会影响准确性。也许尝试形态学

【讨论】：