OpenCV检测轮廓极点(Python C++)

今天分享一个OpenCV检测轮廓极点实例，原图如下，我们需要检测出地图中最大轮廓的上下左右四个极点，并进行标注显示。

第一步：阈值处理分割出地图轮廓

第二步：轮廓筛选，找到我们需要的轮廓

第三步：计算对应轮廓的极点坐标并标注

Python OpenCV源码与效果图如下：

代码语言：javascript复制

import numpy as np
import cv2
from PIL import Image, ImageDraw, ImageFont

font = cv2.FONT_HERSHEY_SIMPLEX

def putText_Chinese(img, text, pt, textColor=(0, 255, 0), textSize=20):
  left, top = pt[0], pt[1]
  if (isinstance(img, np.ndarray)):
    #判断是否OpenCV图片类型
    img = Image.fromarray(cv2.cvtColor(img, cv2.COLOR_BGR2RGB))
    draw = ImageDraw.Draw(img)
    fontText = ImageFont.truetype("simhei.ttf", textSize, encoding="utf-8")
    draw.text((left, top), text, textColor, font=fontText)
    return cv2.cvtColor(np.asarray(img), cv2.COLOR_RGB2BGR)

img = cv2.imread('2.jpg')

cv2.imshow('src',img)

temp = img.copy()

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

ret,thresh = cv2.threshold(gray, 130, 250, cv2.THRESH_BINARY)
cv2.imshow("thres",thresh)

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

for cnt in contours:
  (x, y, w, h) = cv2.boundingRect(cnt)
  if(w > 300 and h > 300):
    left_most = tuple(cnt[cnt[:, :, 0].argmin()][0])
    right_most = tuple(cnt[cnt[:, :, 0].argmax()][0])
    top_most = tuple(cnt[cnt[:, :, 1].argmin()][0])
    bottom_most = tuple(cnt[cnt[:, :, 1].argmax()][0])
    cv2.drawContours(img,cnt,-1,(255,0,0),2)
    cv2.circle(img,left_most,5,(0,255,0),-1, cv2.LINE_AA)
    cv2.circle(img,right_most,5,(0,255,0),-1, cv2.LINE_AA)
    cv2.circle(img,top_most,5,(0,255,0),-1, cv2.LINE_AA)
    cv2.circle(img,bottom_most,5,(0,255,0),-1, cv2.LINE_AA)
  
    img = putText_Chinese(img, "西", left_most, (0, 255, 255), 30)
    img = putText_Chinese(img, "东", right_most, (0, 255, 255), 30)
    img = putText_Chinese(img, "北", top_most, (0, 255, 255), 30)
    img = putText_Chinese(img, "南", bottom_most, (0, 255, 255), 30)
    img = putText_Chinese(img, "中 国", (int(x   w/2),int(y  h/2)), (255, 255, 0), 70)

cv2.imshow('contours', img)

cv2.imwrite('result.bmp',img)

cv2.waitKey(0)

cv2.destroyAllWindows()

程序运行结果：

C OpenCV核心代码如下：

代码语言：javascript复制

box[i] = minAreaRect(Mat(contours[i]));  //计算每个轮廓最小外接矩形
if (box[i].size.width < 50 || box[i].size.height < 50)
  continue;
//计算轮廓极值点
Point extLeft = *min_element(contours[i].begin(), contours[i].end(),
  [](const Point& lhs, const Point& rhs) {
  return lhs.x < rhs.x;
});
Point extRight = *max_element(contours[i].begin(), contours[i].end(),
  [](const Point& lhs, const Point& rhs) {
  return lhs.x < rhs.x;
});
Point extTop = *min_element(contours[i].begin(), contours[i].end(),
  [](const Point& lhs, const Point& rhs) {
  return lhs.y < rhs.y;
});
Point extBot = *max_element(contours[i].begin(), contours[i].end(),
  [](const Point& lhs, const Point& rhs) {
  return lhs.y < rhs.y;
});

opencv

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