opencv提取外部轮廓并在外部加矩形框

#include "stdafx.h"
#include "stdio.h"
#include "Base_process.h"
#include "opencv/cv.h"
#include "opencv/highgui.h"
#include <opencv2/opencv.hpp>
#include <tchar.h>
#include <iostream>
#include <fstream>
 
using namespace std;
using namespace cv;
 
void main()
{
  Mat src = imread("D:\\Recognize_Form_Project\\test_images\\0.jpg");//图片路径/*image180.jpg*/
 
 Mat gray_image;
 cvtColor(src, gray_image, CV_BGR2GRAY);
 imwrite("src.jpg", src);
 
 Mat binary_image;
 adaptiveThreshold(gray_image, binary_image, 255, CV_ADAPTIVE_THRESH_MEAN_C,
 CV_THRESH_BINARY_INV, 25, 10); ///局部自适应二值化函数
 
 imwrite("erzhi.jpg", binary_image);
 
 //去噪
 Mat de_noise = binary_image.clone();
    //中值滤波
 
 medianBlur(binary_image, de_noise, 5);
 
 /////////////////////////  膨胀 ////////////////////
 Mat dilate_img;
 Mat element = getStructuringElement(MORPH_RECT, Size(20, 20/*15, 15*/));
 dilate(de_noise, dilate_img,element);
 imwrite("dilate.jpg", dilate_img);
 
 
 //外部加框
 //检测连通域，每一个连通域以一系列的点表示，FindContours方法只能得到第一个域
 vector<vector<Point>> contours;
 vector<Vec4i> hierarchy;
 findContours(dilate_img, contours, hierarchy, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);//CV_RETR_EXTERNAL只检测外部轮廓，可根据自身需求进行调整
 
 Mat contoursImage(dilate_img.rows, dilate_img.cols, CV_8U, Scalar(255));
 int index = 0;
 for (; index >= 0; index = hierarchy[index][0]) {
 cv::Scalar color(rand() & 255, rand() & 255, rand() & 255);
 // for opencv 2
 // cv::drawContours(dstImage, contours, index, color, CV_FILLED, 8, hierarchy);//CV_FILLED所在位置表示轮廓线条粗细度，如果为负值（如thickness==cv_filled），绘制在轮廓内部
 // for opencv 3
 //cv::drawContours(contoursImage, contours, index, color, cv::FILLED, 8, hierarchy);
 
 cv::drawContours(contoursImage, contours, index, Scalar(0), 1, 8, hierarchy);//描绘字符的外轮廓
 
 Rect rect = boundingRect(contours[index]);//检测外轮廓
 rectangle(contoursImage, rect, Scalar(0,0,255), 3);//对外轮廓加矩形框
 }
 
 
 imwrite("zt.jpg", contoursImage）;
 
 cout << "完成检测";
 
 de_noise.release();
 element.release();
 dilate_img.release();
 binary_image.release();
 gray_image.release();
}