Python OpenCV4获取轮廓最大内切圆和外接圆

为了方便讲解，我们先来创建一个多边形做演示

第一步：创建图像，并绘制一个六边形。代码和生成图像如下：

# Create an image

r = 100

src = np.zeros((4*r, 4*r), dtype=np.uint8)

# Create a sequence of points to make a contour

vert = [None]*6

vert[0] = (3*r//2, int(1.34*r))

vert[1] = (1*r, 2*r)

vert[2] = (3*r//2, int(2.866*r))

vert[3] = (5*r//2, int(2.866*r))

vert[4] = (3*r, 2*r)

vert[5] = (5*r//2, int(1.34*r))

# Draw it in src

for i in range(6):

    cv.line(src, vert[i],  vert[(i+1)%6], ( 255 ), 3)

cv.imshow("src", src)

第二步：查找轮廓，计算图像上的点到轮廓的距离

# Get the contours

_, contours, _ = cv.findContours(src, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)

# Calculate the distances to the contour

raw_dist = np.empty(src.shape, dtype=np.float32)

for i in range(src.shape[0]):

    for j in range(src.shape[1]):

        raw_dist[i,j] = cv.pointPolygonTest(contours[1], (j,i), True)

注意cv.RETR_TREE查找轮廓后轮廓是从外到内的排列顺序，那么contours[1]就是六边形的内边轮廓

第三步：获取轮廓内部距离轮廓最远的点（作为内切圆圆心）和最小距离（作为内切圆半径），绘制内切圆

# 获取最大值即内接圆半径，中心点坐标

minVal, maxVal, _, maxDistPt = cv.minMaxLoc(raw_dist)

minVal = abs(minVal)

maxVal = abs(maxVal)

result = cv.cvtColor(src,cv.COLOR_GRAY2BGR)

cv.circle(result,maxDistPt, np.int(maxVal),(0,255,0), 2, cv.LINE_8, 0)

cv.imshow('result', result)　

最终效果：

当然，如果你还想获取外接圆，直接调用函数cv2.minEnclosingCircle(即可)，下面是代码演示和效果：

# contours[0]对应最外层轮廓
center,radius = cv.minEnclosingCircle(contours[0])
cv.circle(result,(int(center[0]),int(center[1])),int(radius),(0,0,255),2)

完整代码：

import cv2 as cv

import numpy as np

# Create an image

r = 100

src = np.zeros((4*r, 4*r), dtype=np.uint8)

# Create a sequence of points to make a contour

vert = [None]*6

vert[0] = (3*r//2, int(1.34*r))

vert[1] = (1*r, 2*r)

vert[2] = (3*r//2, int(2.866*r))

vert[3] = (5*r//2, int(2.866*r))

vert[4] = (3*r, 2*r)

vert[5] = (5*r//2, int(1.34*r))

# Draw it in src

for i in range(6):

    cv.line(src, vert[i],  vert[(i+1)%6], ( 255 ), 3)

cv.imshow("src", src)

# Get the contours

_, contours, _ = cv.findContours(src, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)

# Calculate the distances to the contour

raw_dist = np.empty(src.shape, dtype=np.float32)

for i in range(src.shape[0]):

    for j in range(src.shape[1]):

        raw_dist[i,j] = cv.pointPolygonTest(contours[1], (j,i), True)

# 获取最大值即内接圆半径，中心点坐标

minVal, maxVal, _, maxDistPt = cv.minMaxLoc(raw_dist)

minVal = abs(minVal)

maxVal = abs(maxVal)

result = cv.cvtColor(src,cv.COLOR_GRAY2BGR)

center,radius = cv.minEnclosingCircle(contours[0])

cv.circle(result,(int(center[0]),int(center[1])),int(radius),(0,0,255),2)

cv.circle(result,maxDistPt, np.int(maxVal),(0,255,0), 2, cv.LINE_8, 0)

cv.imshow('result', result)

cv.waitKey(0)

cv.destroyAllWindows()

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