轮廓发现

轮廓发现是基于图像边缘提取的基础寻找对象轮廓的方法，所以边缘提取的阈值选定会影响最终轮廓发现结果。
相关API：
findContours发现轮廓
drawContours绘制轮廓

操作步骤:

输入图像转为灰度图像
使用Canny进行边缘提取，得到二值图像
使用findContours寻找轮廓
使用drawContours绘制轮廓

#include "stdafx.h"
#include <opencv2/opencv.hpp>
#include <iostream>
#include <vector>
#include <math.h>
using namespace cv;
using namespace std;
void contours(int, void *);
int thread_value = 100;
int thread_max = 255;
RNG rng;
int main(int argc, int ** argv)
{
    src = imread("F:/circle.png");
    if (!src.data) {
        printf("无法加载图片\n");
        return -1;
    }
    namedWindow("input img", CV_WINDOW_AUTOSIZE);
    namedWindow("output img", CV_WINDOW_AUTOSIZE);
    
    cvtColor(src, src, CV_BGR2GRAY);
    imshow("input img", src);
    const char* title = "thread value";
    createTrackbar(title, "output img", &thread_value, thread_max, contours);
    contours(0, 0);
    waitKey(0);
    return 0;
}
void contours(int, void *)
{
    vector<vector<Point>> contours;
    vector<Vec4i> hierarchy;
    Canny(src, dst, thread_value, thread_value * 2, 3, false);
    findContours(dst, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));
    Mat drawImg = Mat::zeros(dst.size(), CV_8UC3);
    for (size_t i = 0; i < contours.size(); i++)
    {
        Scalar color = Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255));
        drawContours(drawImg, contours, i, color, 2, LINE_8, hierarchy, 0, Point(0, 0));
    }
    imshow("output img", drawImg);
}