26、【opencv入门】轮廓查找与绘制（4）——正外接矩形

一、简介

1、使用特定形状的轮廓包围

　　在实际应用中, 经常会有将检测到的轮廓用多边形表示出来的需求, 提取包围轮廓的多边形也方便我们做进一步分析, 轮廓包围主要有一下几种: 轮廓外接矩形、轮廓最小外接矩形(旋转)、轮廓最小包围圆形、轮廓拟合椭圆、轮廓逼近多边形曲线

2、轮廓外接矩形 --- boundingRect()

CV_EXPORTS_W Rect boundingRect(InputArray points);

　　points: 输入的二维点集, 可以填Mat类型或std::vector

　　返回值: Rect类矩形对象

示例：

vector<Rect> boundRect(contours.size());//定义外接矩形集合
int x0 = 0, y0 = 0, w0 = 0, h0 = 0;
for(int i = 0; i < contours.size(); i++)
{
    drawContours(dstImg, contours, i, Scalar(0, 0, 255), 2, 8);
    boundRect[i] = boundingRect(Mat(contours[i]));
    x0 = boundRect[i].x;
    y0 = boundRect[i].y;
    w0 = boundRect[i].width;
    h0 = boundRect[i].height;
    
    rectangle(dstImg, Point(x0, y0), Point(x0 + w0, y0 + h0), Scalar(0, 255, 0), 2, 8);
}

二、外接矩形的查找绘制

//外接矩形的查找绘制
#include "opencv2/opencv.hpp"

using namespace cv;

int main()
{
    //外接矩形的查找绘制
    Mat srcImg =imread("2.jpg");
    imshow("src",srcImg);
    Mat dstImg = srcImg.clone();  //原图备份
    cvtColor(srcImg, srcImg, CV_BGR2GRAY); //转为灰度图
    threshold(srcImg, srcImg, 100, 255, CV_THRESH_BINARY); //二值化

    vector<vector<Point>> contours;  
    vector<Vec4i> hierarcy;
    findContours(srcImg, contours, hierarcy, CV_RETR_EXTERNAL, CHAIN_APPROX_NONE); //查找轮廓
    vector<Rect> boundRect(contours.size()); //定义外接矩形集合
    //drawContours(dstImg, contours, -1, Scalar(0, 0, 255), 2, 8);  //绘制轮廓
    int x0=0, y0=0, w0=0, h0=0;
    for(int i=0; i<contours.size(); i++)
    {
        boundRect[i] = boundingRect((Mat)contours[i]); //查找每个轮廓的外接矩形
        drawContours(dstImg, contours, i, Scalar(0, 0, 255), 2, 8);  //绘制轮廓
        x0 = boundRect[i].x;  //获得第i个外接矩形的左上角的x坐标
        y0 = boundRect[i].y; //获得第i个外接矩形的左上角的y坐标
        w0 = boundRect[i].width; //获得第i个外接矩形的宽度
        h0 = boundRect[i].height; //获得第i个外接矩形的高度
        rectangle(dstImg, Point(x0, y0), Point(x0+w0, y0+h0), Scalar(0, 255, 0), 2, 8); //绘制第i个外接矩形
    }
    imshow("boundRect", dstImg);
    waitKey(0); 
    return 0;
}

三、分割硬币轮廓并计数

//分割硬币轮廓并计数
#include "opencv2/opencv.hpp"
#include<iostream>

using namespace cv;
using namespace std;

int main()
{
    //分割硬币轮廓
    Mat srcImg =imread("3.png");
    imshow("src", srcImg);
    Mat dstImg = srcImg.clone();  //原图备份
    cvtColor(srcImg, srcImg, CV_BGR2GRAY); //转为灰度图
    threshold(srcImg, srcImg, 100, 255, CV_THRESH_BINARY); //二值化
    Mat element = getStructuringElement(MORPH_RECT, Size(3, 3), Point(-1, -1)); //获得结构元素
    dilate(srcImg, srcImg, element); //膨胀操作
    imshow("dilate",srcImg);

    vector<vector<Point>> contours;  
    vector<Vec4i> hierarcy;
    findContours(srcImg, contours, hierarcy, CV_RETR_EXTERNAL, CHAIN_APPROX_NONE); //查找轮廓
    vector<Rect> boundRect(contours.size()); //定义外接矩形集合
    int x0=0, y0=0, w0=0, h0=0,num=0;
    for(int i=0; i<contours.size(); i++)
    {
        boundRect[i] = boundingRect((Mat)contours[i]); //查找每个轮廓的外接矩形
        drawContours(dstImg, contours, i, Scalar(0, 0, 255), 2, 8);  //绘制轮廓
        x0 = boundRect[i].x;  
        y0 = boundRect[i].y; 
        w0 = boundRect[i].width; 
        h0 = boundRect[i].height; 
        if(w0>30 && h0>30)//筛选
        {
            rectangle(dstImg, Point(x0, y0), Point(x0+w0, y0+h0), Scalar(0, 255, 0), 2, 8); //绘制第i个外接矩形
            num++;
        }
    }
    cout<<"硬币数量："<<num;
    imshow("boundRect", dstImg);
    waitKey(0); 
    return 0;
}

 四、简单车牌字符分隔

//简单车牌字符分割
#include "opencv2/opencv.hpp"

using namespace cv;

int main()
{
    //---简单车牌字符分隔
    Mat srcImg =imread("12.jpg");
    Mat dstImg = srcImg.clone();  //原图备份
    medianBlur(srcImg, srcImg, 5);  //中值滤波
    cvtColor(srcImg, srcImg, CV_BGR2GRAY); //转为灰度图
    threshold(srcImg, srcImg, 100, 255, CV_THRESH_BINARY); //二值化
    imshow("threshold", srcImg);
    imwrite("F://car0.jpg", srcImg);

    vector<vector<Point>> contours;  
    vector<Vec4i> hierarcy;
    findContours(srcImg, contours, hierarcy, CV_RETR_TREE, CHAIN_APPROX_NONE); //查找所有轮廓
    vector<Rect> boundRect(contours.size()); //定义外接矩形集合
    int x0=0, y0=0, w0=0, h0=0;
    for(int i=0; i<contours.size(); i++)
    {
        boundRect[i] = boundingRect((Mat)contours[i]); //查找每个轮廓的外接矩形
        x0 = boundRect[i].x;  
        y0 = boundRect[i].y; 
        w0 = boundRect[i].width; 
        h0 = boundRect[i].height; 
        if(w0>srcImg.cols/12 && w0<srcImg.cols/5 && h0>srcImg.rows/6 && h0<srcImg.rows*5/6)
        {
            char pic_name[10];
            sprintf(pic_name, "F:\\%d.bmp", i);
            Mat ROI = dstImg(Rect(x0, y0, w0, h0));
            imwrite(pic_name, ROI);
            rectangle(dstImg, Point(x0, y0), Point(x0+w0, y0+h0), Scalar(0, 255, 0), 2, 8); //绘制第i个外接矩形
        }
    }
    imshow("boundRect", dstImg);
    waitKey(0);
    return 0;
}