一、分析

貼出應用圖片以供直觀了解

紅色部分，因圖而異（某些參數，根據圖片的不同需要進行相應的修改）

二、代碼

 1 #include "opencv2/opencv.hpp"
 2 #include<iostream>
 3 using namespace cv;
 4 using namespace std;
 5 
 6 void main(){
 7     Mat img=imread("E://9.jpg");
 8     int thres_min=220;  //二值化最小閾值
 9     if(!img.empty()){
10         //二值化
11         threshold(img, img, thres_min, 255, THRESH_BINARY);
12         imshow("img_thres",img);
13         //img備份
14         Mat copy=img.clone();//拷貝原圖，且不會隨着原圖改變
15         cvtColor(copy,copy,CV_BGR2GRAY);//彩色圖轉灰度圖
16         threshold(copy, copy, thres_min, 255, THRESH_BINARY_INV);//反轉：白色變黑色，黑色變白色
17         imshow("copy", copy);
18         //查找copy的輪廓
19         vector<vector<Point>>contours;
20         findContours(copy, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
21         //將輪廓畫在全黑圖像上
22         Mat draw;
23         draw = Mat::zeros(img.size(), CV_32FC1);//定義一個img大小的全黑圖像
24         drawContours(draw, contours, 0, Scalar(255), -2);
25         imshow("img2", draw);
26         //進行膨脹腐蝕操作
27         Mat dilated, eroded;
28         Mat kernel=getStructuringElement(MORPH_RECT,Size(19,19));//定義結構元素
29         dilate(draw, dilated, kernel, Point(-1,-1), 2);//膨脹兩次
30         imshow("dilate", dilated);
31         erode(dilated, eroded,  kernel, Point(-1,-1), 2);
32         imshow("erode", eroded);
33         //膨脹腐蝕相減
34         Mat diff;
35         absdiff(dilated, eroded, diff);
36         diff.convertTo(diff, CV_8UC1);//轉換為單通道圖（即灰度圖）
37         imshow("diff", diff);
38         //在差異圖diff中查找輪廓,然后在原圖中繪制輪廓
39         vector<vector<Point>>contours2;
40         findContours(diff, contours2, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
41         drawContours(img, contours2, 0, Scalar(0,255,0),-1);//-1表示繪制輪廓內部，正數表示輪廓線條粗細
42         imshow("result", img);
43     }
44     waitKey(0);
45     destroyAllWindows();
46 }